Merge branch 'master' into ticket_2501ticket_2501

Conflicts:
	lib/sqlalchemy/orm/mapper.py

1 files changed, 3273 insertions, 0 deletions

diff --git a/lib/sqlalchemy/sql/schema.py b/lib/sqlalchemy/sql/schema.py
new file mode 100644
index 000000000..ba38b5070
--- /dev/null
+++ b/lib/sqlalchemy/sql/schema.py
@@ -0,0 +1,3273 @@
+# sql/schema.py
+# Copyright (C) 2005-2014 the SQLAlchemy authors and contributors <see AUTHORS file>
+#
+# This module is part of SQLAlchemy and is released under
+# the MIT License: http://www.opensource.org/licenses/mit-license.php
+
+"""The schema module provides the building blocks for database metadata.
+
+Each element within this module describes a database entity which can be
+created and dropped, or is otherwise part of such an entity.  Examples include
+tables, columns, sequences, and indexes.
+
+All entities are subclasses of :class:`~sqlalchemy.schema.SchemaItem`, and as
+defined in this module they are intended to be agnostic of any vendor-specific
+constructs.
+
+A collection of entities are grouped into a unit called
+:class:`~sqlalchemy.schema.MetaData`. MetaData serves as a logical grouping of
+schema elements, and can also be associated with an actual database connection
+such that operations involving the contained elements can contact the database
+as needed.
+
+Two of the elements here also build upon their "syntactic" counterparts, which
+are defined in :class:`~sqlalchemy.sql.expression.`, specifically
+:class:`~sqlalchemy.schema.Table` and :class:`~sqlalchemy.schema.Column`.
+Since these objects are part of the SQL expression language, they are usable
+as components in SQL expressions.
+
+"""
+
+import inspect
+from .. import exc, util, event, inspection
+from .base import SchemaEventTarget, DialectKWArgs
+from . import visitors
+from . import type_api
+from .base import _bind_or_error, ColumnCollection
+from .elements import ClauseElement, ColumnClause, _truncated_label, \
+                        _as_truncated, TextClause, _literal_as_text,\
+                        ColumnElement, _find_columns, quoted_name
+from .selectable import TableClause
+import collections
+import sqlalchemy
+from . import ddl
+
+RETAIN_SCHEMA = util.symbol('retain_schema')
+
+
+def _get_table_key(name, schema):
+    if schema is None:
+        return name
+    else:
+        return schema + "." + name
+
+
+
+@inspection._self_inspects
+class SchemaItem(SchemaEventTarget, visitors.Visitable):
+    """Base class for items that define a database schema."""
+
+    __visit_name__ = 'schema_item'
+
+    def _execute_on_connection(self, connection, multiparams, params):
+        return connection._execute_default(self, multiparams, params)
+
+    def _init_items(self, *args):
+        """Initialize the list of child items for this SchemaItem."""
+
+        for item in args:
+            if item is not None:
+                item._set_parent_with_dispatch(self)
+
+    def get_children(self, **kwargs):
+        """used to allow SchemaVisitor access"""
+        return []
+
+    def __repr__(self):
+        return util.generic_repr(self)
+
+    @property
+    @util.deprecated('0.9', 'Use ``<obj>.name.quote``')
+    def quote(self):
+        """Return the value of the ``quote`` flag passed
+        to this schema object, for those schema items which
+        have a ``name`` field.
+
+        """
+
+        return self.name.quote
+
+    @util.memoized_property
+    def info(self):
+        """Info dictionary associated with the object, allowing user-defined
+        data to be associated with this :class:`.SchemaItem`.
+
+        The dictionary is automatically generated when first accessed.
+        It can also be specified in the constructor of some objects,
+        such as :class:`.Table` and :class:`.Column`.
+
+        """
+        return {}
+
+    def _schema_item_copy(self, schema_item):
+        if 'info' in self.__dict__:
+            schema_item.info = self.info.copy()
+        schema_item.dispatch._update(self.dispatch)
+        return schema_item
+
+
+class Table(DialectKWArgs, SchemaItem, TableClause):
+    """Represent a table in a database.
+
+    e.g.::
+
+        mytable = Table("mytable", metadata,
+                        Column('mytable_id', Integer, primary_key=True),
+                        Column('value', String(50))
+                   )
+
+    The :class:`.Table` object constructs a unique instance of itself based
+    on its name and optional schema name within the given
+    :class:`.MetaData` object. Calling the :class:`.Table`
+    constructor with the same name and same :class:`.MetaData` argument
+    a second time will return the *same* :class:`.Table` object - in this way
+    the :class:`.Table` constructor acts as a registry function.
+
+    .. seealso::
+
+        :ref:`metadata_describing` - Introduction to database metadata
+
+    Constructor arguments are as follows:
+
+    :param name: The name of this table as represented in the database.
+
+        The table name, along with the value of the ``schema`` parameter,
+        forms a key which uniquely identifies this :class:`.Table` within
+        the owning :class:`.MetaData` collection.
+        Additional calls to :class:`.Table` with the same name, metadata,
+        and schema name will return the same :class:`.Table` object.
+
+        Names which contain no upper case characters
+        will be treated as case insensitive names, and will not be quoted
+        unless they are a reserved word or contain special characters.
+        A name with any number of upper case characters is considered
+        to be case sensitive, and will be sent as quoted.
+
+        To enable unconditional quoting for the table name, specify the flag
+        ``quote=True`` to the constructor, or use the :class:`.quoted_name`
+        construct to specify the name.
+
+    :param metadata: a :class:`.MetaData` object which will contain this
+        table.  The metadata is used as a point of association of this table
+        with other tables which are referenced via foreign key.  It also
+        may be used to associate this table with a particular
+        :class:`.Connectable`.
+
+    :param \*args: Additional positional arguments are used primarily
+        to add the list of :class:`.Column` objects contained within this
+        table. Similar to the style of a CREATE TABLE statement, other
+        :class:`.SchemaItem` constructs may be added here, including
+        :class:`.PrimaryKeyConstraint`, and :class:`.ForeignKeyConstraint`.
+
+    :param autoload: Defaults to False: the Columns for this table should
+        be reflected from the database. Usually there will be no Column
+        objects in the constructor if this property is set.
+
+    :param autoload_replace: If ``True``, when using ``autoload=True``
+        and ``extend_existing=True``,
+        replace ``Column`` objects already present in the ``Table`` that's
+        in the ``MetaData`` registry with
+        what's reflected.  Otherwise, all existing columns will be
+        excluded from the reflection process.    Note that this does
+        not impact ``Column`` objects specified in the same call to ``Table``
+        which includes ``autoload``, those always take precedence.
+        Defaults to ``True``.
+
+        .. versionadded:: 0.7.5
+
+    :param autoload_with: If autoload==True, this is an optional Engine
+        or Connection instance to be used for the table reflection. If
+        ``None``, the underlying MetaData's bound connectable will be used.
+
+    :param extend_existing: When ``True``, indicates that if this
+        :class:`.Table` is already present in the given :class:`.MetaData`,
+        apply further arguments within the constructor to the existing
+        :class:`.Table`.
+
+        If ``extend_existing`` or ``keep_existing`` are not set, an error is
+        raised if additional table modifiers are specified when
+        the given :class:`.Table` is already present in the :class:`.MetaData`.
+
+        .. versionchanged:: 0.7.4
+            ``extend_existing`` will work in conjunction
+            with ``autoload=True`` to run a new reflection operation against
+            the database; new :class:`.Column` objects will be produced
+            from database metadata to replace those existing with the same
+            name, and additional :class:`.Column` objects not present
+            in the :class:`.Table` will be added.
+
+        As is always the case with ``autoload=True``, :class:`.Column`
+        objects can be specified in the same :class:`.Table` constructor,
+        which will take precedence.  I.e.::
+
+            Table("mytable", metadata,
+                        Column('y', Integer),
+                        extend_existing=True,
+                        autoload=True,
+                        autoload_with=engine
+                    )
+
+        The above will overwrite all columns within ``mytable`` which
+        are present in the database, except for ``y`` which will be used as is
+        from the above definition.   If the ``autoload_replace`` flag
+        is set to False, no existing columns will be replaced.
+
+    :param implicit_returning: True by default - indicates that
+        RETURNING can be used by default to fetch newly inserted primary key
+        values, for backends which support this.  Note that
+        create_engine() also provides an implicit_returning flag.
+
+    :param include_columns: A list of strings indicating a subset of
+        columns to be loaded via the ``autoload`` operation; table columns who
+        aren't present in this list will not be represented on the resulting
+        ``Table`` object. Defaults to ``None`` which indicates all columns
+        should be reflected.
+
+    :param info: Optional data dictionary which will be populated into the
+        :attr:`.SchemaItem.info` attribute of this object.
+
+    :param keep_existing: When ``True``, indicates that if this Table
+        is already present in the given :class:`.MetaData`, ignore
+        further arguments within the constructor to the existing
+        :class:`.Table`, and return the :class:`.Table` object as
+        originally created. This is to allow a function that wishes
+        to define a new :class:`.Table` on first call, but on
+        subsequent calls will return the same :class:`.Table`,
+        without any of the declarations (particularly constraints)
+        being applied a second time. Also see extend_existing.
+
+        If extend_existing or keep_existing are not set, an error is
+        raised if additional table modifiers are specified when
+        the given :class:`.Table` is already present in the :class:`.MetaData`.
+
+    :param listeners: A list of tuples of the form ``(<eventname>, <fn>)``
+        which will be passed to :func:`.event.listen` upon construction.
+        This alternate hook to :func:`.event.listen` allows the establishment
+        of a listener function specific to this :class:`.Table` before
+        the "autoload" process begins.  Particularly useful for
+        the :meth:`.DDLEvents.column_reflect` event::
+
+            def listen_for_reflect(table, column_info):
+                "handle the column reflection event"
+                # ...
+
+            t = Table(
+                'sometable',
+                autoload=True,
+                listeners=[
+                    ('column_reflect', listen_for_reflect)
+                ])
+
+    :param mustexist: When ``True``, indicates that this Table must already
+        be present in the given :class:`.MetaData` collection, else
+        an exception is raised.
+
+    :param prefixes:
+        A list of strings to insert after CREATE in the CREATE TABLE
+        statement.  They will be separated by spaces.
+
+    :param quote: Force quoting of this table's name on or off, corresponding
+        to ``True`` or ``False``.  When left at its default of ``None``,
+        the column identifier will be quoted according to whether the name is
+        case sensitive (identifiers with at least one upper case character are
+        treated as case sensitive), or if it's a reserved word.  This flag
+        is only needed to force quoting of a reserved word which is not known
+        by the SQLAlchemy dialect.
+
+    :param quote_schema: same as 'quote' but applies to the schema identifier.
+
+    :param schema: The schema name for this table, which is required if
+        the table resides in a schema other than the default selected schema
+        for the engine's database connection.  Defaults to ``None``.
+
+        The quoting rules for the schema name are the same as those for the
+        ``name`` parameter, in that quoting is applied for reserved words or
+        case-sensitive names; to enable unconditional quoting for the
+        schema name, specify the flag
+        ``quote_schema=True`` to the constructor, or use the :class:`.quoted_name`
+        construct to specify the name.
+
+    :param useexisting: Deprecated.  Use extend_existing.
+
+    :param \**kw: Additional keyword arguments not mentioned above are
+        dialect specific, and passed in the form ``<dialectname>_<argname>``.
+        See the documentation regarding an individual dialect at
+        :ref:`dialect_toplevel` for detail on documented arguments.
+
+    """
+
+    __visit_name__ = 'table'
+
+    def __new__(cls, *args, **kw):
+        if not args:
+            # python3k pickle seems to call this
+            return object.__new__(cls)
+
+        try:
+            name, metadata, args = args[0], args[1], args[2:]
+        except IndexError:
+            raise TypeError("Table() takes at least two arguments")
+
+        schema = kw.get('schema', None)
+        if schema is None:
+            schema = metadata.schema
+        keep_existing = kw.pop('keep_existing', False)
+        extend_existing = kw.pop('extend_existing', False)
+        if 'useexisting' in kw:
+            msg = "useexisting is deprecated.  Use extend_existing."
+            util.warn_deprecated(msg)
+            if extend_existing:
+                msg = "useexisting is synonymous with extend_existing."
+                raise exc.ArgumentError(msg)
+            extend_existing = kw.pop('useexisting', False)
+
+        if keep_existing and extend_existing:
+            msg = "keep_existing and extend_existing are mutually exclusive."
+            raise exc.ArgumentError(msg)
+
+        mustexist = kw.pop('mustexist', False)
+        key = _get_table_key(name, schema)
+        if key in metadata.tables:
+            if not keep_existing and not extend_existing and bool(args):
+                raise exc.InvalidRequestError(
+                    "Table '%s' is already defined for this MetaData "
+                    "instance.  Specify 'extend_existing=True' "
+                    "to redefine "
+                    "options and columns on an "
+                    "existing Table object." % key)
+            table = metadata.tables[key]
+            if extend_existing:
+                table._init_existing(*args, **kw)
+            return table
+        else:
+            if mustexist:
+                raise exc.InvalidRequestError(
+                    "Table '%s' not defined" % (key))
+            table = object.__new__(cls)
+            table.dispatch.before_parent_attach(table, metadata)
+            metadata._add_table(name, schema, table)
+            try:
+                table._init(name, metadata, *args, **kw)
+                table.dispatch.after_parent_attach(table, metadata)
+                return table
+            except:
+                #metadata._remove_table(name, schema)
+                raise
+
+
+    @property
+    @util.deprecated('0.9', 'Use ``table.schema.quote``')
+    def quote_schema(self):
+        """Return the value of the ``quote_schema`` flag passed
+        to this :class:`.Table`.
+        """
+
+        return self.schema.quote
+
+    def __init__(self, *args, **kw):
+        """Constructor for :class:`~.schema.Table`.
+
+        This method is a no-op.   See the top-level
+        documentation for :class:`~.schema.Table`
+        for constructor arguments.
+
+        """
+        # __init__ is overridden to prevent __new__ from
+        # calling the superclass constructor.
+
+    def _init(self, name, metadata, *args, **kwargs):
+        super(Table, self).__init__(quoted_name(name, kwargs.pop('quote', None)))
+        self.metadata = metadata
+
+        self.schema = kwargs.pop('schema', None)
+        if self.schema is None:
+            self.schema = metadata.schema
+        else:
+            quote_schema = kwargs.pop('quote_schema', None)
+            self.schema = quoted_name(self.schema, quote_schema)
+
+        self.indexes = set()
+        self.constraints = set()
+        self._columns = ColumnCollection()
+        PrimaryKeyConstraint()._set_parent_with_dispatch(self)
+        self.foreign_keys = set()
+        self._extra_dependencies = set()
+        if self.schema is not None:
+            self.fullname = "%s.%s" % (self.schema, self.name)
+        else:
+            self.fullname = self.name
+
+        autoload = kwargs.pop('autoload', False)
+        autoload_with = kwargs.pop('autoload_with', None)
+        # this argument is only used with _init_existing()
+        kwargs.pop('autoload_replace', True)
+        include_columns = kwargs.pop('include_columns', None)
+
+        self.implicit_returning = kwargs.pop('implicit_returning', True)
+
+        if 'info' in kwargs:
+            self.info = kwargs.pop('info')
+        if 'listeners' in kwargs:
+            listeners = kwargs.pop('listeners')
+            for evt, fn in listeners:
+                event.listen(self, evt, fn)
+
+        self._prefixes = kwargs.pop('prefixes', [])
+
+        self._extra_kwargs(**kwargs)
+
+        # load column definitions from the database if 'autoload' is defined
+        # we do it after the table is in the singleton dictionary to support
+        # circular foreign keys
+        if autoload:
+            self._autoload(metadata, autoload_with, include_columns)
+
+        # initialize all the column, etc. objects.  done after reflection to
+        # allow user-overrides
+        self._init_items(*args)
+
+    def _autoload(self, metadata, autoload_with, include_columns,
+                  exclude_columns=()):
+
+        if autoload_with:
+            autoload_with.run_callable(
+                autoload_with.dialect.reflecttable,
+                self, include_columns, exclude_columns
+            )
+        else:
+            bind = _bind_or_error(metadata,
+                    msg="No engine is bound to this Table's MetaData. "
+                    "Pass an engine to the Table via "
+                    "autoload_with=<someengine>, "
+                    "or associate the MetaData with an engine via "
+                    "metadata.bind=<someengine>")
+            bind.run_callable(
+                    bind.dialect.reflecttable,
+                    self, include_columns, exclude_columns
+                )
+
+    @property
+    def _sorted_constraints(self):
+        """Return the set of constraints as a list, sorted by creation
+        order.
+
+        """
+        return sorted(self.constraints, key=lambda c: c._creation_order)
+
+    def _init_existing(self, *args, **kwargs):
+        autoload = kwargs.pop('autoload', False)
+        autoload_with = kwargs.pop('autoload_with', None)
+        autoload_replace = kwargs.pop('autoload_replace', True)
+        schema = kwargs.pop('schema', None)
+        if schema and schema != self.schema:
+            raise exc.ArgumentError(
+                "Can't change schema of existing table from '%s' to '%s'",
+                (self.schema, schema))
+
+        include_columns = kwargs.pop('include_columns', None)
+
+        if include_columns is not None:
+            for c in self.c:
+                if c.name not in include_columns:
+                    self._columns.remove(c)
+
+        for key in ('quote', 'quote_schema'):
+            if key in kwargs:
+                raise exc.ArgumentError(
+                    "Can't redefine 'quote' or 'quote_schema' arguments")
+
+        if 'info' in kwargs:
+            self.info = kwargs.pop('info')
+
+        if autoload:
+            if not autoload_replace:
+                exclude_columns = [c.name for c in self.c]
+            else:
+                exclude_columns = ()
+            self._autoload(
+                self.metadata, autoload_with, include_columns, exclude_columns)
+
+        self._extra_kwargs(**kwargs)
+        self._init_items(*args)
+
+    def _extra_kwargs(self, **kwargs):
+        self._validate_dialect_kwargs(kwargs)
+
+    def _init_collections(self):
+        pass
+
+    @util.memoized_property
+    def _autoincrement_column(self):
+        for col in self.primary_key:
+            if col.autoincrement and \
+                col.type._type_affinity is not None and \
+                issubclass(col.type._type_affinity, type_api.INTEGERTYPE._type_affinity) and \
+                (not col.foreign_keys or col.autoincrement == 'ignore_fk') and \
+                isinstance(col.default, (type(None), Sequence)) and \
+                (col.server_default is None or col.server_default.reflected):
+                return col
+
+    @property
+    def key(self):
+        """Return the 'key' for this :class:`.Table`.
+
+        This value is used as the dictionary key within the
+        :attr:`.MetaData.tables` collection.   It is typically the same
+        as that of :attr:`.Table.name` for a table with no :attr:`.Table.schema`
+        set; otherwise it is typically of the form ``schemaname.tablename``.
+
+        """
+        return _get_table_key(self.name, self.schema)
+
+    def __repr__(self):
+        return "Table(%s)" % ', '.join(
+            [repr(self.name)] + [repr(self.metadata)] +
+            [repr(x) for x in self.columns] +
+            ["%s=%s" % (k, repr(getattr(self, k))) for k in ['schema']])
+
+    def __str__(self):
+        return _get_table_key(self.description, self.schema)
+
+    @property
+    def bind(self):
+        """Return the connectable associated with this Table."""
+
+        return self.metadata and self.metadata.bind or None
+
+    def add_is_dependent_on(self, table):
+        """Add a 'dependency' for this Table.
+
+        This is another Table object which must be created
+        first before this one can, or dropped after this one.
+
+        Usually, dependencies between tables are determined via
+        ForeignKey objects.   However, for other situations that
+        create dependencies outside of foreign keys (rules, inheriting),
+        this method can manually establish such a link.
+
+        """
+        self._extra_dependencies.add(table)
+
+    def append_column(self, column):
+        """Append a :class:`~.schema.Column` to this :class:`~.schema.Table`.
+
+        The "key" of the newly added :class:`~.schema.Column`, i.e. the
+        value of its ``.key`` attribute, will then be available
+        in the ``.c`` collection of this :class:`~.schema.Table`, and the
+        column definition will be included in any CREATE TABLE, SELECT,
+        UPDATE, etc. statements generated from this :class:`~.schema.Table`
+        construct.
+
+        Note that this does **not** change the definition of the table
+        as it exists within any underlying database, assuming that
+        table has already been created in the database.   Relational
+        databases support the addition of columns to existing tables
+        using the SQL ALTER command, which would need to be
+        emitted for an already-existing table that doesn't contain
+        the newly added column.
+
+        """
+
+        column._set_parent_with_dispatch(self)
+
+    def append_constraint(self, constraint):
+        """Append a :class:`~.schema.Constraint` to this
+        :class:`~.schema.Table`.
+
+        This has the effect of the constraint being included in any
+        future CREATE TABLE statement, assuming specific DDL creation
+        events have not been associated with the given
+        :class:`~.schema.Constraint` object.
+
+        Note that this does **not** produce the constraint within the
+        relational database automatically, for a table that already exists
+        in the database.   To add a constraint to an
+        existing relational database table, the SQL ALTER command must
+        be used.  SQLAlchemy also provides the
+        :class:`.AddConstraint` construct which can produce this SQL when
+        invoked as an executable clause.
+
+        """
+
+        constraint._set_parent_with_dispatch(self)
+
+    def append_ddl_listener(self, event_name, listener):
+        """Append a DDL event listener to this ``Table``.
+
+        .. deprecated:: 0.7
+            See :class:`.DDLEvents`.
+
+        """
+
+        def adapt_listener(target, connection, **kw):
+            listener(event_name, target, connection)
+
+        event.listen(self, "" + event_name.replace('-', '_'), adapt_listener)
+
+    def _set_parent(self, metadata):
+        metadata._add_table(self.name, self.schema, self)
+        self.metadata = metadata
+
+    def get_children(self, column_collections=True,
+                                schema_visitor=False, **kw):
+        if not schema_visitor:
+            return TableClause.get_children(
+                self, column_collections=column_collections, **kw)
+        else:
+            if column_collections:
+                return list(self.columns)
+            else:
+                return []
+
+    def exists(self, bind=None):
+        """Return True if this table exists."""
+
+        if bind is None:
+            bind = _bind_or_error(self)
+
+        return bind.run_callable(bind.dialect.has_table,
+                                self.name, schema=self.schema)
+
+    def create(self, bind=None, checkfirst=False):
+        """Issue a ``CREATE`` statement for this
+        :class:`.Table`, using the given :class:`.Connectable`
+        for connectivity.
+
+        .. seealso::
+
+            :meth:`.MetaData.create_all`.
+
+        """
+
+        if bind is None:
+            bind = _bind_or_error(self)
+        bind._run_visitor(ddl.SchemaGenerator,
+                            self,
+                            checkfirst=checkfirst)
+
+    def drop(self, bind=None, checkfirst=False):
+        """Issue a ``DROP`` statement for this
+        :class:`.Table`, using the given :class:`.Connectable`
+        for connectivity.
+
+        .. seealso::
+
+            :meth:`.MetaData.drop_all`.
+
+        """
+        if bind is None:
+            bind = _bind_or_error(self)
+        bind._run_visitor(ddl.SchemaDropper,
+                            self,
+                            checkfirst=checkfirst)
+
+    def tometadata(self, metadata, schema=RETAIN_SCHEMA):
+        """Return a copy of this :class:`.Table` associated with a different
+        :class:`.MetaData`.
+
+        E.g.::
+
+            some_engine = create_engine("sqlite:///some.db")
+
+            # create two metadata
+            meta1 = MetaData()
+            meta2 = MetaData()
+
+            # load 'users' from the sqlite engine
+            users_table = Table('users', meta1, autoload=True,
+                                    autoload_with=some_engine)
+
+            # create the same Table object for the plain metadata
+            users_table_2 = users_table.tometadata(meta2)
+
+        :param metadata: Target :class:`.MetaData` object.
+        :param schema: Optional string name of a target schema, or
+         ``None`` for no schema.  The :class:`.Table` object will be
+         given this schema name upon copy.   Defaults to the special
+         symbol :attr:`.RETAIN_SCHEMA` which indicates no change should be
+         made to the schema name of the resulting :class:`.Table`.
+
+        """
+
+        if schema is RETAIN_SCHEMA:
+            schema = self.schema
+        elif schema is None:
+            schema = metadata.schema
+        key = _get_table_key(self.name, schema)
+        if key in metadata.tables:
+            util.warn("Table '%s' already exists within the given "
+                      "MetaData - not copying." % self.description)
+            return metadata.tables[key]
+
+        args = []
+        for c in self.columns:
+            args.append(c.copy(schema=schema))
+        table = Table(
+            self.name, metadata, schema=schema,
+            *args, **self.kwargs
+            )
+        for c in self.constraints:
+            table.append_constraint(c.copy(schema=schema, target_table=table))
+
+        for index in self.indexes:
+            # skip indexes that would be generated
+            # by the 'index' flag on Column
+            if len(index.columns) == 1 and \
+                    list(index.columns)[0].index:
+                continue
+            Index(index.name,
+                  unique=index.unique,
+                  *[table.c[col] for col in index.columns.keys()],
+                  **index.kwargs)
+        return self._schema_item_copy(table)
+
+
+class Column(SchemaItem, ColumnClause):
+    """Represents a column in a database table."""
+
+    __visit_name__ = 'column'
+
+    def __init__(self, *args, **kwargs):
+        """
+        Construct a new ``Column`` object.
+
+        :param name: The name of this column as represented in the database.
+          This argument may be the first positional argument, or specified
+          via keyword.
+
+          Names which contain no upper case characters
+          will be treated as case insensitive names, and will not be quoted
+          unless they are a reserved word.  Names with any number of upper
+          case characters will be quoted and sent exactly.  Note that this
+          behavior applies even for databases which standardize upper
+          case names as case insensitive such as Oracle.
+
+          The name field may be omitted at construction time and applied
+          later, at any time before the Column is associated with a
+          :class:`.Table`.  This is to support convenient
+          usage within the :mod:`~sqlalchemy.ext.declarative` extension.
+
+        :param type\_: The column's type, indicated using an instance which
+          subclasses :class:`~sqlalchemy.types.TypeEngine`.  If no arguments
+          are required for the type, the class of the type can be sent
+          as well, e.g.::
+
+            # use a type with arguments
+            Column('data', String(50))
+
+            # use no arguments
+            Column('level', Integer)
+
+          The ``type`` argument may be the second positional argument
+          or specified by keyword.
+
+          If the ``type`` is ``None`` or is omitted, it will first default to the special
+          type :class:`.NullType`.  If and when this :class:`.Column` is
+          made to refer to another column using :class:`.ForeignKey`
+          and/or :class:`.ForeignKeyConstraint`, the type of the remote-referenced
+          column will be copied to this column as well, at the moment that
+          the foreign key is resolved against that remote :class:`.Column`
+          object.
+
+          .. versionchanged:: 0.9.0
+            Support for propagation of type to a :class:`.Column` from its
+            :class:`.ForeignKey` object has been improved and should be
+            more reliable and timely.
+
+        :param \*args: Additional positional arguments include various
+          :class:`.SchemaItem` derived constructs which will be applied
+          as options to the column.  These include instances of
+          :class:`.Constraint`, :class:`.ForeignKey`, :class:`.ColumnDefault`,
+          and :class:`.Sequence`.  In some cases an equivalent keyword
+          argument is available such as ``server_default``, ``default``
+          and ``unique``.
+
+        :param autoincrement: This flag may be set to ``False`` to
+          indicate an integer primary key column that should not be
+          considered to be the "autoincrement" column, that is
+          the integer primary key column which generates values
+          implicitly upon INSERT and whose value is usually returned
+          via the DBAPI cursor.lastrowid attribute.   It defaults
+          to ``True`` to satisfy the common use case of a table
+          with a single integer primary key column.  If the table
+          has a composite primary key consisting of more than one
+          integer column, set this flag to True only on the
+          column that should be considered "autoincrement".
+
+          The setting *only* has an effect for columns which are:
+
+          * Integer derived (i.e. INT, SMALLINT, BIGINT).
+
+          * Part of the primary key
+
+          * Are not referenced by any foreign keys, unless
+            the value is specified as ``'ignore_fk'``
+
+            .. versionadded:: 0.7.4
+
+          * have no server side or client side defaults (with the exception
+            of Postgresql SERIAL).
+
+          The setting has these two effects on columns that meet the
+          above criteria:
+
+          * DDL issued for the column will include database-specific
+            keywords intended to signify this column as an
+            "autoincrement" column, such as AUTO INCREMENT on MySQL,
+            SERIAL on Postgresql, and IDENTITY on MS-SQL.  It does
+            *not* issue AUTOINCREMENT for SQLite since this is a
+            special SQLite flag that is not required for autoincrementing
+            behavior.  See the SQLite dialect documentation for
+            information on SQLite's AUTOINCREMENT.
+
+          * The column will be considered to be available as
+            cursor.lastrowid or equivalent, for those dialects which
+            "post fetch" newly inserted identifiers after a row has
+            been inserted (SQLite, MySQL, MS-SQL).  It does not have
+            any effect in this regard for databases that use sequences
+            to generate primary key identifiers (i.e. Firebird, Postgresql,
+            Oracle).
+
+          .. versionchanged:: 0.7.4
+              ``autoincrement`` accepts a special value ``'ignore_fk'``
+              to indicate that autoincrementing status regardless of foreign
+              key references.  This applies to certain composite foreign key
+              setups, such as the one demonstrated in the ORM documentation
+              at :ref:`post_update`.
+
+        :param default: A scalar, Python callable, or
+            :class:`.ColumnElement` expression representing the
+            *default value* for this column, which will be invoked upon insert
+            if this column is otherwise not specified in the VALUES clause of
+            the insert. This is a shortcut to using :class:`.ColumnDefault` as
+            a positional argument; see that class for full detail on the
+            structure of the argument.
+
+            Contrast this argument to ``server_default`` which creates a
+            default generator on the database side.
+
+        :param doc: optional String that can be used by the ORM or similar
+            to document attributes.   This attribute does not render SQL
+            comments (a future attribute 'comment' will achieve that).
+
+        :param key: An optional string identifier which will identify this
+            ``Column`` object on the :class:`.Table`. When a key is provided,
+            this is the only identifier referencing the ``Column`` within the
+            application, including ORM attribute mapping; the ``name`` field
+            is used only when rendering SQL.
+
+        :param index: When ``True``, indicates that the column is indexed.
+            This is a shortcut for using a :class:`.Index` construct on the
+            table. To specify indexes with explicit names or indexes that
+            contain multiple columns, use the :class:`.Index` construct
+            instead.
+
+        :param info: Optional data dictionary which will be populated into the
+            :attr:`.SchemaItem.info` attribute of this object.
+
+        :param nullable: If set to the default of ``True``, indicates the
+            column will be rendered as allowing NULL, else it's rendered as
+            NOT NULL. This parameter is only used when issuing CREATE TABLE
+            statements.
+
+        :param onupdate: A scalar, Python callable, or
+            :class:`~sqlalchemy.sql.expression.ClauseElement` representing a
+            default value to be applied to the column within UPDATE
+            statements, which wil be invoked upon update if this column is not
+            present in the SET clause of the update. This is a shortcut to
+            using :class:`.ColumnDefault` as a positional argument with
+            ``for_update=True``.
+
+        :param primary_key: If ``True``, marks this column as a primary key
+            column. Multiple columns can have this flag set to specify
+            composite primary keys. As an alternative, the primary key of a
+            :class:`.Table` can be specified via an explicit
+            :class:`.PrimaryKeyConstraint` object.
+
+        :param server_default: A :class:`.FetchedValue` instance, str, Unicode
+            or :func:`~sqlalchemy.sql.expression.text` construct representing
+            the DDL DEFAULT value for the column.
+
+            String types will be emitted as-is, surrounded by single quotes::
+
+                Column('x', Text, server_default="val")
+
+                x TEXT DEFAULT 'val'
+
+            A :func:`~sqlalchemy.sql.expression.text` expression will be
+            rendered as-is, without quotes::
+
+                Column('y', DateTime, server_default=text('NOW()'))
+
+                y DATETIME DEFAULT NOW()
+
+            Strings and text() will be converted into a :class:`.DefaultClause`
+            object upon initialization.
+
+            Use :class:`.FetchedValue` to indicate that an already-existing
+            column will generate a default value on the database side which
+            will be available to SQLAlchemy for post-fetch after inserts. This
+            construct does not specify any DDL and the implementation is left
+            to the database, such as via a trigger.
+
+        :param server_onupdate:   A :class:`.FetchedValue` instance
+             representing a database-side default generation function. This
+             indicates to SQLAlchemy that a newly generated value will be
+             available after updates. This construct does not specify any DDL
+             and the implementation is left to the database, such as via a
+             trigger.
+
+        :param quote: Force quoting of this column's name on or off,
+             corresponding to ``True`` or ``False``. When left at its default
+             of ``None``, the column identifier will be quoted according to
+             whether the name is case sensitive (identifiers with at least one
+             upper case character are treated as case sensitive), or if it's a
+             reserved word. This flag is only needed to force quoting of a
+             reserved word which is not known by the SQLAlchemy dialect.
+
+        :param unique: When ``True``, indicates that this column contains a
+             unique constraint, or if ``index`` is ``True`` as well, indicates
+             that the :class:`.Index` should be created with the unique flag.
+             To specify multiple columns in the constraint/index or to specify
+             an explicit name, use the :class:`.UniqueConstraint` or
+             :class:`.Index` constructs explicitly.
+
+        :param system: When ``True``, indicates this is a "system" column,
+             that is a column which is automatically made available by the
+             database, and should not be included in the columns list for a
+             ``CREATE TABLE`` statement.
+
+             For more elaborate scenarios where columns should be conditionally
+             rendered differently on different backends, consider custom
+             compilation rules for :class:`.CreateColumn`.
+
+             ..versionadded:: 0.8.3 Added the ``system=True`` parameter to
+               :class:`.Column`.
+
+        """
+
+        name = kwargs.pop('name', None)
+        type_ = kwargs.pop('type_', None)
+        args = list(args)
+        if args:
+            if isinstance(args[0], util.string_types):
+                if name is not None:
+                    raise exc.ArgumentError(
+                        "May not pass name positionally and as a keyword.")
+                name = args.pop(0)
+        if args:
+            coltype = args[0]
+
+            if hasattr(coltype, "_sqla_type"):
+                if type_ is not None:
+                    raise exc.ArgumentError(
+                        "May not pass type_ positionally and as a keyword.")
+                type_ = args.pop(0)
+
+        if name is not None:
+            name = quoted_name(name, kwargs.pop('quote', None))
+        elif "quote" in kwargs:
+            raise exc.ArgumentError("Explicit 'name' is required when "
+                            "sending 'quote' argument")
+
+        super(Column, self).__init__(name, type_)
+        self.key = kwargs.pop('key', name)
+        self.primary_key = kwargs.pop('primary_key', False)
+        self.nullable = kwargs.pop('nullable', not self.primary_key)
+        self.default = kwargs.pop('default', None)
+        self.server_default = kwargs.pop('server_default', None)
+        self.server_onupdate = kwargs.pop('server_onupdate', None)
+
+        # these default to None because .index and .unique is *not*
+        # an informational flag about Column - there can still be an
+        # Index or UniqueConstraint referring to this Column.
+        self.index = kwargs.pop('index', None)
+        self.unique = kwargs.pop('unique', None)
+
+        self.system = kwargs.pop('system', False)
+        self.doc = kwargs.pop('doc', None)
+        self.onupdate = kwargs.pop('onupdate', None)
+        self.autoincrement = kwargs.pop('autoincrement', True)
+        self.constraints = set()
+        self.foreign_keys = set()
+
+        # check if this Column is proxying another column
+        if '_proxies' in kwargs:
+            self._proxies = kwargs.pop('_proxies')
+        # otherwise, add DDL-related events
+        elif isinstance(self.type, SchemaEventTarget):
+            self.type._set_parent_with_dispatch(self)
+
+        if self.default is not None:
+            if isinstance(self.default, (ColumnDefault, Sequence)):
+                args.append(self.default)
+            else:
+                if getattr(self.type, '_warn_on_bytestring', False):
+                    if isinstance(self.default, util.binary_type):
+                        util.warn("Unicode column received non-unicode "
+                                  "default value.")
+                args.append(ColumnDefault(self.default))
+
+        if self.server_default is not None:
+            if isinstance(self.server_default, FetchedValue):
+                args.append(self.server_default._as_for_update(False))
+            else:
+                args.append(DefaultClause(self.server_default))
+
+        if self.onupdate is not None:
+            if isinstance(self.onupdate, (ColumnDefault, Sequence)):
+                args.append(self.onupdate)
+            else:
+                args.append(ColumnDefault(self.onupdate, for_update=True))
+
+        if self.server_onupdate is not None:
+            if isinstance(self.server_onupdate, FetchedValue):
+                args.append(self.server_onupdate._as_for_update(True))
+            else:
+                args.append(DefaultClause(self.server_onupdate,
+                                            for_update=True))
+        self._init_items(*args)
+
+        util.set_creation_order(self)
+
+        if 'info' in kwargs:
+            self.info = kwargs.pop('info')
+
+        if kwargs:
+            raise exc.ArgumentError(
+                "Unknown arguments passed to Column: " + repr(list(kwargs)))
+
+#    @property
+#    def quote(self):
+#        return getattr(self.name, "quote", None)
+
+    def __str__(self):
+        if self.name is None:
+            return "(no name)"
+        elif self.table is not None:
+            if self.table.named_with_column:
+                return (self.table.description + "." + self.description)
+            else:
+                return self.description
+        else:
+            return self.description
+
+    def references(self, column):
+        """Return True if this Column references the given column via foreign
+        key."""
+
+        for fk in self.foreign_keys:
+            if fk.column.proxy_set.intersection(column.proxy_set):
+                return True
+        else:
+            return False
+
+    def append_foreign_key(self, fk):
+        fk._set_parent_with_dispatch(self)
+
+    def __repr__(self):
+        kwarg = []
+        if self.key != self.name:
+            kwarg.append('key')
+        if self.primary_key:
+            kwarg.append('primary_key')
+        if not self.nullable:
+            kwarg.append('nullable')
+        if self.onupdate:
+            kwarg.append('onupdate')
+        if self.default:
+            kwarg.append('default')
+        if self.server_default:
+            kwarg.append('server_default')
+        return "Column(%s)" % ', '.join(
+            [repr(self.name)] + [repr(self.type)] +
+            [repr(x) for x in self.foreign_keys if x is not None] +
+            [repr(x) for x in self.constraints] +
+            [(self.table is not None and "table=<%s>" %
+                    self.table.description or "table=None")] +
+            ["%s=%s" % (k, repr(getattr(self, k))) for k in kwarg])
+
+    def _set_parent(self, table):
+        if not self.name:
+            raise exc.ArgumentError(
+                "Column must be constructed with a non-blank name or "
+                "assign a non-blank .name before adding to a Table.")
+        if self.key is None:
+            self.key = self.name
+
+        existing = getattr(self, 'table', None)
+        if existing is not None and existing is not table:
+            raise exc.ArgumentError(
+                    "Column object already assigned to Table '%s'" %
+                    existing.description)
+
+        if self.key in table._columns:
+            col = table._columns.get(self.key)
+            if col is not self:
+                for fk in col.foreign_keys:
+                    table.foreign_keys.remove(fk)
+                    if fk.constraint in table.constraints:
+                        # this might have been removed
+                        # already, if it's a composite constraint
+                        # and more than one col being replaced
+                        table.constraints.remove(fk.constraint)
+
+        table._columns.replace(self)
+
+        if self.primary_key:
+            table.primary_key._replace(self)
+            Table._autoincrement_column._reset(table)
+        elif self.key in table.primary_key:
+            raise exc.ArgumentError(
+                "Trying to redefine primary-key column '%s' as a "
+                "non-primary-key column on table '%s'" % (
+                self.key, table.fullname))
+        self.table = table
+
+        if self.index:
+            if isinstance(self.index, util.string_types):
+                raise exc.ArgumentError(
+                    "The 'index' keyword argument on Column is boolean only. "
+                    "To create indexes with a specific name, create an "
+                    "explicit Index object external to the Table.")
+            Index(_truncated_label('ix_%s' % self._label),
+                                    self, unique=bool(self.unique))
+        elif self.unique:
+            if isinstance(self.unique, util.string_types):
+                raise exc.ArgumentError(
+                    "The 'unique' keyword argument on Column is boolean "
+                    "only. To create unique constraints or indexes with a "
+                    "specific name, append an explicit UniqueConstraint to "
+                    "the Table's list of elements, or create an explicit "
+                    "Index object external to the Table.")
+            table.append_constraint(UniqueConstraint(self.key))
+
+        fk_key = (table.key, self.key)
+        if fk_key in self.table.metadata._fk_memos:
+            for fk in self.table.metadata._fk_memos[fk_key]:
+                fk._set_remote_table(table)
+
+    def _on_table_attach(self, fn):
+        if self.table is not None:
+            fn(self, self.table)
+        event.listen(self, 'after_parent_attach', fn)
+
+    def copy(self, **kw):
+        """Create a copy of this ``Column``, unitialized.
+
+        This is used in ``Table.tometadata``.
+
+        """
+
+        # Constraint objects plus non-constraint-bound ForeignKey objects
+        args = \
+            [c.copy(**kw) for c in self.constraints] + \
+            [c.copy(**kw) for c in self.foreign_keys if not c.constraint]
+
+        type_ = self.type
+        if isinstance(type_, SchemaEventTarget):
+            type_ = type_.copy(**kw)
+
+        c = self._constructor(
+                name=self.name,
+                type_=type_,
+                key=self.key,
+                primary_key=self.primary_key,
+                nullable=self.nullable,
+                unique=self.unique,
+                system=self.system,
+                #quote=self.quote,
+                index=self.index,
+                autoincrement=self.autoincrement,
+                default=self.default,
+                server_default=self.server_default,
+                onupdate=self.onupdate,
+                server_onupdate=self.server_onupdate,
+                doc=self.doc,
+                *args
+                )
+        return self._schema_item_copy(c)
+
+    def _make_proxy(self, selectable, name=None, key=None,
+                            name_is_truncatable=False, **kw):
+        """Create a *proxy* for this column.
+
+        This is a copy of this ``Column`` referenced by a different parent
+        (such as an alias or select statement).  The column should
+        be used only in select scenarios, as its full DDL/default
+        information is not transferred.
+
+        """
+        fk = [ForeignKey(f.column, _constraint=f.constraint)
+                for f in self.foreign_keys]
+        if name is None and self.name is None:
+            raise exc.InvalidRequestError("Cannot initialize a sub-selectable"
+                    " with this Column object until it's 'name' has "
+                    "been assigned.")
+        try:
+            c = self._constructor(
+                _as_truncated(name or self.name) if \
+                                name_is_truncatable else (name or self.name),
+                self.type,
+                key=key if key else name if name else self.key,
+                primary_key=self.primary_key,
+                nullable=self.nullable,
+                _proxies=[self], *fk)
+        except TypeError:
+            util.raise_from_cause(
+                TypeError(
+                    "Could not create a copy of this %r object.  "
+                    "Ensure the class includes a _constructor() "
+                    "attribute or method which accepts the "
+                    "standard Column constructor arguments, or "
+                    "references the Column class itself." % self.__class__)
+                )
+
+        c.table = selectable
+        selectable._columns.add(c)
+        if selectable._is_clone_of is not None:
+            c._is_clone_of = selectable._is_clone_of.columns[c.key]
+        if self.primary_key:
+            selectable.primary_key.add(c)
+        c.dispatch.after_parent_attach(c, selectable)
+        return c
+
+    def get_children(self, schema_visitor=False, **kwargs):
+        if schema_visitor:
+            return [x for x in (self.default, self.onupdate)
+                    if x is not None] + \
+                list(self.foreign_keys) + list(self.constraints)
+        else:
+            return ColumnClause.get_children(self, **kwargs)
+
+
+class ForeignKey(DialectKWArgs, SchemaItem):
+    """Defines a dependency between two columns.
+
+    ``ForeignKey`` is specified as an argument to a :class:`.Column` object,
+    e.g.::
+
+        t = Table("remote_table", metadata,
+            Column("remote_id", ForeignKey("main_table.id"))
+        )
+
+    Note that ``ForeignKey`` is only a marker object that defines
+    a dependency between two columns.   The actual constraint
+    is in all cases represented by the :class:`.ForeignKeyConstraint`
+    object.   This object will be generated automatically when
+    a ``ForeignKey`` is associated with a :class:`.Column` which
+    in turn is associated with a :class:`.Table`.   Conversely,
+    when :class:`.ForeignKeyConstraint` is applied to a :class:`.Table`,
+    ``ForeignKey`` markers are automatically generated to be
+    present on each associated :class:`.Column`, which are also
+    associated with the constraint object.
+
+    Note that you cannot define a "composite" foreign key constraint,
+    that is a constraint between a grouping of multiple parent/child
+    columns, using ``ForeignKey`` objects.   To define this grouping,
+    the :class:`.ForeignKeyConstraint` object must be used, and applied
+    to the :class:`.Table`.   The associated ``ForeignKey`` objects
+    are created automatically.
+
+    The ``ForeignKey`` objects associated with an individual
+    :class:`.Column` object are available in the `foreign_keys` collection
+    of that column.
+
+    Further examples of foreign key configuration are in
+    :ref:`metadata_foreignkeys`.
+
+    """
+
+    __visit_name__ = 'foreign_key'
+
+    def __init__(self, column, _constraint=None, use_alter=False, name=None,
+                    onupdate=None, ondelete=None, deferrable=None,
+                    initially=None, link_to_name=False, match=None,
+                    **dialect_kw):
+        """
+        Construct a column-level FOREIGN KEY.
+
+        The :class:`.ForeignKey` object when constructed generates a
+        :class:`.ForeignKeyConstraint` which is associated with the parent
+        :class:`.Table` object's collection of constraints.
+
+        :param column: A single target column for the key relationship. A
+            :class:`.Column` object or a column name as a string:
+            ``tablename.columnkey`` or ``schema.tablename.columnkey``.
+            ``columnkey`` is the ``key`` which has been assigned to the column
+            (defaults to the column name itself), unless ``link_to_name`` is
+            ``True`` in which case the rendered name of the column is used.
+
+            .. versionadded:: 0.7.4
+                Note that if the schema name is not included, and the
+                underlying :class:`.MetaData` has a "schema", that value will
+                be used.
+
+        :param name: Optional string. An in-database name for the key if
+            `constraint` is not provided.
+
+        :param onupdate: Optional string. If set, emit ON UPDATE <value> when
+            issuing DDL for this constraint. Typical values include CASCADE,
+            DELETE and RESTRICT.
+
+        :param ondelete: Optional string. If set, emit ON DELETE <value> when
+            issuing DDL for this constraint. Typical values include CASCADE,
+            DELETE and RESTRICT.
+
+        :param deferrable: Optional bool. If set, emit DEFERRABLE or NOT
+            DEFERRABLE when issuing DDL for this constraint.
+
+        :param initially: Optional string. If set, emit INITIALLY <value> when
+            issuing DDL for this constraint.
+
+        :param link_to_name: if True, the string name given in ``column`` is
+            the rendered name of the referenced column, not its locally
+            assigned ``key``.
+
+        :param use_alter: passed to the underlying
+            :class:`.ForeignKeyConstraint` to indicate the constraint should be
+            generated/dropped externally from the CREATE TABLE/ DROP TABLE
+            statement. See that classes' constructor for details.
+
+        :param match: Optional string. If set, emit MATCH <value> when issuing
+            DDL for this constraint. Typical values include SIMPLE, PARTIAL
+            and FULL.
+
+        :param \**dialect_kw:  Additional keyword arguments are dialect specific,
+            and passed in the form ``<dialectname>_<argname>``.  The arguments
+            are ultimately handled by a corresponding :class:`.ForeignKeyConstraint`.
+            See the documentation regarding an individual dialect at
+            :ref:`dialect_toplevel` for detail on documented arguments.
+
+            .. versionadded:: 0.9.2
+
+        """
+
+        self._colspec = column
+        if isinstance(self._colspec, util.string_types):
+            self._table_column = None
+        else:
+            if hasattr(self._colspec, '__clause_element__'):
+                self._table_column = self._colspec.__clause_element__()
+            else:
+                self._table_column = self._colspec
+
+            if not isinstance(self._table_column, ColumnClause):
+                raise exc.ArgumentError(
+                        "String, Column, or Column-bound argument "
+                        "expected, got %r" % self._table_column)
+            elif not isinstance(self._table_column.table, (util.NoneType, TableClause)):
+                raise exc.ArgumentError(
+                        "ForeignKey received Column not bound "
+                        "to a Table, got: %r" % self._table_column.table
+                    )
+
+        # the linked ForeignKeyConstraint.
+        # ForeignKey will create this when parent Column
+        # is attached to a Table, *or* ForeignKeyConstraint
+        # object passes itself in when creating ForeignKey
+        # markers.
+        self.constraint = _constraint
+        self.parent = None
+        self.use_alter = use_alter
+        self.name = name
+        self.onupdate = onupdate
+        self.ondelete = ondelete
+        self.deferrable = deferrable
+        self.initially = initially
+        self.link_to_name = link_to_name
+        self.match = match
+        self._unvalidated_dialect_kw = dialect_kw
+
+    def __repr__(self):
+        return "ForeignKey(%r)" % self._get_colspec()
+
+    def copy(self, schema=None):
+        """Produce a copy of this :class:`.ForeignKey` object.
+
+        The new :class:`.ForeignKey` will not be bound
+        to any :class:`.Column`.
+
+        This method is usually used by the internal
+        copy procedures of :class:`.Column`, :class:`.Table`,
+        and :class:`.MetaData`.
+
+        :param schema: The returned :class:`.ForeignKey` will
+          reference the original table and column name, qualified
+          by the given string schema name.
+
+        """
+
+        fk = ForeignKey(
+                self._get_colspec(schema=schema),
+                use_alter=self.use_alter,
+                name=self.name,
+                onupdate=self.onupdate,
+                ondelete=self.ondelete,
+                deferrable=self.deferrable,
+                initially=self.initially,
+                link_to_name=self.link_to_name,
+                match=self.match,
+                **self._unvalidated_dialect_kw
+                )
+        return self._schema_item_copy(fk)
+
+
+    def _get_colspec(self, schema=None):
+        """Return a string based 'column specification' for this
+        :class:`.ForeignKey`.
+
+        This is usually the equivalent of the string-based "tablename.colname"
+        argument first passed to the object's constructor.
+
+        """
+        if schema:
+            _schema, tname, colname = self._column_tokens
+            return "%s.%s.%s" % (schema, tname, colname)
+        elif self._table_column is not None:
+            return "%s.%s" % (
+                    self._table_column.table.fullname, self._table_column.key)
+        else:
+            return self._colspec
+
+
+    def _table_key(self):
+        if self._table_column is not None:
+            if self._table_column.table is None:
+                return None
+            else:
+                return self._table_column.table.key
+        else:
+            schema, tname, colname = self._column_tokens
+            return _get_table_key(tname, schema)
+
+
+
+    target_fullname = property(_get_colspec)
+
+    def references(self, table):
+        """Return True if the given :class:`.Table` is referenced by this
+        :class:`.ForeignKey`."""
+
+        return table.corresponding_column(self.column) is not None
+
+    def get_referent(self, table):
+        """Return the :class:`.Column` in the given :class:`.Table`
+        referenced by this :class:`.ForeignKey`.
+
+        Returns None if this :class:`.ForeignKey` does not reference the given
+        :class:`.Table`.
+
+        """
+
+        return table.corresponding_column(self.column)
+
+    @util.memoized_property
+    def _column_tokens(self):
+        """parse a string-based _colspec into its component parts."""
+
+        m = self._colspec.split('.')
+        if m is None:
+            raise exc.ArgumentError(
+                "Invalid foreign key column specification: %s" %
+                self._colspec)
+        if (len(m) == 1):
+            tname = m.pop()
+            colname = None
+        else:
+            colname = m.pop()
+            tname = m.pop()
+
+        # A FK between column 'bar' and table 'foo' can be
+        # specified as 'foo', 'foo.bar', 'dbo.foo.bar',
+        # 'otherdb.dbo.foo.bar'. Once we have the column name and
+        # the table name, treat everything else as the schema
+        # name. Some databases (e.g. Sybase) support
+        # inter-database foreign keys. See tickets#1341 and --
+        # indirectly related -- Ticket #594. This assumes that '.'
+        # will never appear *within* any component of the FK.
+
+        if (len(m) > 0):
+            schema = '.'.join(m)
+        else:
+            schema = None
+        return schema, tname, colname
+
+    def _resolve_col_tokens(self):
+        if self.parent is None:
+            raise exc.InvalidRequestError(
+                    "this ForeignKey object does not yet have a "
+                    "parent Column associated with it.")
+
+        elif self.parent.table is None:
+            raise exc.InvalidRequestError(
+                    "this ForeignKey's parent column is not yet associated "
+                    "with a Table.")
+
+        parenttable = self.parent.table
+
+        # assertion, can be commented out.
+        # basically Column._make_proxy() sends the actual
+        # target Column to the ForeignKey object, so the
+        # string resolution here is never called.
+        for c in self.parent.base_columns:
+            if isinstance(c, Column):
+                assert c.table is parenttable
+                break
+        else:
+            assert False
+        ######################
+
+        schema, tname, colname = self._column_tokens
+
+        if schema is None and parenttable.metadata.schema is not None:
+            schema = parenttable.metadata.schema
+
+        tablekey = _get_table_key(tname, schema)
+        return parenttable, tablekey, colname
+
+
+    def _link_to_col_by_colstring(self, parenttable, table, colname):
+        if not hasattr(self.constraint, '_referred_table'):
+            self.constraint._referred_table = table
+        else:
+            assert self.constraint._referred_table is table
+
+        _column = None
+        if colname is None:
+            # colname is None in the case that ForeignKey argument
+            # was specified as table name only, in which case we
+            # match the column name to the same column on the
+            # parent.
+            key = self.parent
+            _column = table.c.get(self.parent.key, None)
+        elif self.link_to_name:
+            key = colname
+            for c in table.c:
+                if c.name == colname:
+                    _column = c
+        else:
+            key = colname
+            _column = table.c.get(colname, None)
+
+        if _column is None:
+            raise exc.NoReferencedColumnError(
+                "Could not initialize target column for ForeignKey '%s' on table '%s': "
+                "table '%s' has no column named '%s'" % (
+                self._colspec, parenttable.name, table.name, key),
+                table.name, key)
+
+        self._set_target_column(_column)
+
+    def _set_target_column(self, column):
+        # propagate TypeEngine to parent if it didn't have one
+        if self.parent.type._isnull:
+            self.parent.type = column.type
+
+        # super-edgy case, if other FKs point to our column,
+        # they'd get the type propagated out also.
+        if isinstance(self.parent.table, Table):
+            fk_key = (self.parent.table.key, self.parent.key)
+            if fk_key in self.parent.table.metadata._fk_memos:
+                for fk in self.parent.table.metadata._fk_memos[fk_key]:
+                    if fk.parent.type._isnull:
+                        fk.parent.type = column.type
+
+        self.column = column
+
+    @util.memoized_property
+    def column(self):
+        """Return the target :class:`.Column` referenced by this
+        :class:`.ForeignKey`.
+
+        If no target column has been established, an exception
+        is raised.
+
+        .. versionchanged:: 0.9.0
+            Foreign key target column resolution now occurs as soon as both
+            the ForeignKey object and the remote Column to which it refers
+            are both associated with the same MetaData object.
+
+        """
+
+        if isinstance(self._colspec, util.string_types):
+
+            parenttable, tablekey, colname = self._resolve_col_tokens()
+
+            if tablekey not in parenttable.metadata:
+                raise exc.NoReferencedTableError(
+                    "Foreign key associated with column '%s' could not find "
+                    "table '%s' with which to generate a "
+                    "foreign key to target column '%s'" %
+                    (self.parent, tablekey, colname),
+                    tablekey)
+            elif parenttable.key not in parenttable.metadata:
+                raise exc.InvalidRequestError(
+                    "Table %s is no longer associated with its "
+                    "parent MetaData" % parenttable)
+            else:
+                raise exc.NoReferencedColumnError(
+                    "Could not initialize target column for "
+                    "ForeignKey '%s' on table '%s': "
+                    "table '%s' has no column named '%s'" % (
+                    self._colspec, parenttable.name, tablekey, colname),
+                    tablekey, colname)
+        elif hasattr(self._colspec, '__clause_element__'):
+            _column = self._colspec.__clause_element__()
+            return _column
+        else:
+            _column = self._colspec
+            return _column
+
+    def _set_parent(self, column):
+        if self.parent is not None and self.parent is not column:
+            raise exc.InvalidRequestError(
+                    "This ForeignKey already has a parent !")
+        self.parent = column
+        self.parent.foreign_keys.add(self)
+        self.parent._on_table_attach(self._set_table)
+
+    def _set_remote_table(self, table):
+        parenttable, tablekey, colname = self._resolve_col_tokens()
+        self._link_to_col_by_colstring(parenttable, table, colname)
+        self.constraint._validate_dest_table(table)
+
+    def _remove_from_metadata(self, metadata):
+        parenttable, table_key, colname = self._resolve_col_tokens()
+        fk_key = (table_key, colname)
+
+        if self in metadata._fk_memos[fk_key]:
+            # TODO: no test coverage for self not in memos
+            metadata._fk_memos[fk_key].remove(self)
+
+    def _set_table(self, column, table):
+        # standalone ForeignKey - create ForeignKeyConstraint
+        # on the hosting Table when attached to the Table.
+        if self.constraint is None and isinstance(table, Table):
+            self.constraint = ForeignKeyConstraint(
+                [], [], use_alter=self.use_alter, name=self.name,
+                onupdate=self.onupdate, ondelete=self.ondelete,
+                deferrable=self.deferrable, initially=self.initially,
+                match=self.match,
+                **self._unvalidated_dialect_kw
+                )
+            self.constraint._elements[self.parent] = self
+            self.constraint._set_parent_with_dispatch(table)
+        table.foreign_keys.add(self)
+
+        # set up remote ".column" attribute, or a note to pick it
+        # up when the other Table/Column shows up
+        if isinstance(self._colspec, util.string_types):
+            parenttable, table_key, colname = self._resolve_col_tokens()
+            fk_key = (table_key, colname)
+            if table_key in parenttable.metadata.tables:
+                table = parenttable.metadata.tables[table_key]
+                try:
+                    self._link_to_col_by_colstring(parenttable, table, colname)
+                except exc.NoReferencedColumnError:
+                    # this is OK, we'll try later
+                    pass
+            parenttable.metadata._fk_memos[fk_key].append(self)
+        elif hasattr(self._colspec, '__clause_element__'):
+            _column = self._colspec.__clause_element__()
+            self._set_target_column(_column)
+        else:
+            _column = self._colspec
+            self._set_target_column(_column)
+
+
+
+class _NotAColumnExpr(object):
+    def _not_a_column_expr(self):
+        raise exc.InvalidRequestError(
+                "This %s cannot be used directly "
+                "as a column expression." % self.__class__.__name__)
+
+    __clause_element__ = self_group = lambda self: self._not_a_column_expr()
+    _from_objects = property(lambda self: self._not_a_column_expr())
+
+
+class DefaultGenerator(_NotAColumnExpr, SchemaItem):
+    """Base class for column *default* values."""
+
+    __visit_name__ = 'default_generator'
+
+    is_sequence = False
+    is_server_default = False
+    column = None
+
+    def __init__(self, for_update=False):
+        self.for_update = for_update
+
+    def _set_parent(self, column):
+        self.column = column
+        if self.for_update:
+            self.column.onupdate = self
+        else:
+            self.column.default = self
+
+    def execute(self, bind=None, **kwargs):
+        if bind is None:
+            bind = _bind_or_error(self)
+        return bind._execute_default(self, **kwargs)
+
+    @property
+    def bind(self):
+        """Return the connectable associated with this default."""
+        if getattr(self, 'column', None) is not None:
+            return self.column.table.bind
+        else:
+            return None
+
+
+class ColumnDefault(DefaultGenerator):
+    """A plain default value on a column.
+
+    This could correspond to a constant, a callable function,
+    or a SQL clause.
+
+    :class:`.ColumnDefault` is generated automatically
+    whenever the ``default``, ``onupdate`` arguments of
+    :class:`.Column` are used.  A :class:`.ColumnDefault`
+    can be passed positionally as well.
+
+    For example, the following::
+
+        Column('foo', Integer, default=50)
+
+    Is equivalent to::
+
+        Column('foo', Integer, ColumnDefault(50))
+
+
+    """
+
+    def __init__(self, arg, **kwargs):
+        """"Construct a new :class:`.ColumnDefault`.
+
+
+        :param arg: argument representing the default value.
+         May be one of the following:
+
+         * a plain non-callable Python value, such as a
+           string, integer, boolean, or other simple type.
+           The default value will be used as is each time.
+         * a SQL expression, that is one which derives from
+           :class:`.ColumnElement`.  The SQL expression will
+           be rendered into the INSERT or UPDATE statement,
+           or in the case of a primary key column when
+           RETURNING is not used may be
+           pre-executed before an INSERT within a SELECT.
+         * A Python callable.  The function will be invoked for each
+           new row subject to an INSERT or UPDATE.
+           The callable must accept exactly
+           zero or one positional arguments.  The one-argument form
+           will receive an instance of the :class:`.ExecutionContext`,
+           which provides contextual information as to the current
+           :class:`.Connection` in use as well as the current
+           statement and parameters.
+
+        """
+        super(ColumnDefault, self).__init__(**kwargs)
+        if isinstance(arg, FetchedValue):
+            raise exc.ArgumentError(
+                "ColumnDefault may not be a server-side default type.")
+        if util.callable(arg):
+            arg = self._maybe_wrap_callable(arg)
+        self.arg = arg
+
+    @util.memoized_property
+    def is_callable(self):
+        return util.callable(self.arg)
+
+    @util.memoized_property
+    def is_clause_element(self):
+        return isinstance(self.arg, ClauseElement)
+
+    @util.memoized_property
+    def is_scalar(self):
+        return not self.is_callable and \
+                    not self.is_clause_element and \
+                    not self.is_sequence
+
+    def _maybe_wrap_callable(self, fn):
+        """Wrap callables that don't accept a context.
+
+        The alternative here is to require that
+        a simple callable passed to "default" would need
+        to be of the form "default=lambda ctx: datetime.now".
+        That is the more "correct" way to go, but the case
+        of using a zero-arg callable for "default" is so
+        much more prominent than the context-specific one
+        I'm having trouble justifying putting that inconvenience
+        on everyone.
+
+        """
+        if inspect.isfunction(fn) or inspect.ismethod(fn):
+            inspectable = fn
+        elif inspect.isclass(fn):
+            inspectable = fn.__init__
+        elif hasattr(fn, '__call__'):
+            inspectable = fn.__call__
+        else:
+            # probably not inspectable, try anyways.
+            inspectable = fn
+        try:
+            argspec = inspect.getargspec(inspectable)
+        except TypeError:
+            return lambda ctx: fn()
+
+        defaulted = argspec[3] is not None and len(argspec[3]) or 0
+        positionals = len(argspec[0]) - defaulted
+
+        # Py3K compat - no unbound methods
+        if inspect.ismethod(inspectable) or inspect.isclass(fn):
+            positionals -= 1
+
+        if positionals == 0:
+            return lambda ctx: fn()
+        elif positionals == 1:
+            return fn
+        else:
+            raise exc.ArgumentError(
+                "ColumnDefault Python function takes zero or one "
+                "positional arguments")
+
+    def _visit_name(self):
+        if self.for_update:
+            return "column_onupdate"
+        else:
+            return "column_default"
+    __visit_name__ = property(_visit_name)
+
+    def __repr__(self):
+        return "ColumnDefault(%r)" % self.arg
+
+
+class Sequence(DefaultGenerator):
+    """Represents a named database sequence.
+
+    The :class:`.Sequence` object represents the name and configurational
+    parameters of a database sequence.   It also represents
+    a construct that can be "executed" by a SQLAlchemy :class:`.Engine`
+    or :class:`.Connection`, rendering the appropriate "next value" function
+    for the target database and returning a result.
+
+    The :class:`.Sequence` is typically associated with a primary key column::
+
+        some_table = Table('some_table', metadata,
+            Column('id', Integer, Sequence('some_table_seq'), primary_key=True)
+        )
+
+    When CREATE TABLE is emitted for the above :class:`.Table`, if the
+    target platform supports sequences, a CREATE SEQUENCE statement will
+    be emitted as well.   For platforms that don't support sequences,
+    the :class:`.Sequence` construct is ignored.
+
+    .. seealso::
+
+        :class:`.CreateSequence`
+
+        :class:`.DropSequence`
+
+    """
+
+    __visit_name__ = 'sequence'
+
+    is_sequence = True
+
+    def __init__(self, name, start=None, increment=None, schema=None,
+                 optional=False, quote=None, metadata=None,
+                 quote_schema=None,
+                 for_update=False):
+        """Construct a :class:`.Sequence` object.
+
+        :param name: The name of the sequence.
+        :param start: the starting index of the sequence.  This value is
+         used when the CREATE SEQUENCE command is emitted to the database
+         as the value of the "START WITH" clause.   If ``None``, the
+         clause is omitted, which on most platforms indicates a starting
+         value of 1.
+        :param increment: the increment value of the sequence.  This
+         value is used when the CREATE SEQUENCE command is emitted to
+         the database as the value of the "INCREMENT BY" clause.  If ``None``,
+         the clause is omitted, which on most platforms indicates an
+         increment of 1.
+        :param schema: Optional schema name for the sequence, if located
+         in a schema other than the default.
+        :param optional: boolean value, when ``True``, indicates that this
+         :class:`.Sequence` object only needs to be explicitly generated
+         on backends that don't provide another way to generate primary
+         key identifiers.  Currently, it essentially means, "don't create
+         this sequence on the Postgresql backend, where the SERIAL keyword
+         creates a sequence for us automatically".
+        :param quote: boolean value, when ``True`` or ``False``, explicitly
+         forces quoting of the schema name on or off.  When left at its
+         default of ``None``, normal quoting rules based on casing and reserved
+         words take place.
+        :param quote_schema: set the quoting preferences for the ``schema``
+         name.
+        :param metadata: optional :class:`.MetaData` object which will be
+         associated with this :class:`.Sequence`.  A :class:`.Sequence`
+         that is associated with a :class:`.MetaData` gains access to the
+         ``bind`` of that :class:`.MetaData`, meaning the
+         :meth:`.Sequence.create` and :meth:`.Sequence.drop` methods will
+         make usage of that engine automatically.
+
+         .. versionchanged:: 0.7
+             Additionally, the appropriate CREATE SEQUENCE/
+             DROP SEQUENCE DDL commands will be emitted corresponding to this
+             :class:`.Sequence` when :meth:`.MetaData.create_all` and
+             :meth:`.MetaData.drop_all` are invoked.
+
+         Note that when a :class:`.Sequence` is applied to a :class:`.Column`,
+         the :class:`.Sequence` is automatically associated with the
+         :class:`.MetaData` object of that column's parent :class:`.Table`,
+         when that association is made.   The :class:`.Sequence` will then
+         be subject to automatic CREATE SEQUENCE/DROP SEQUENCE corresponding
+         to when the :class:`.Table` object itself is created or dropped,
+         rather than that of the :class:`.MetaData` object overall.
+        :param for_update: Indicates this :class:`.Sequence`, when associated
+         with a :class:`.Column`, should be invoked for UPDATE statements
+         on that column's table, rather than for INSERT statements, when
+         no value is otherwise present for that column in the statement.
+
+        """
+        super(Sequence, self).__init__(for_update=for_update)
+        self.name = quoted_name(name, quote)
+        self.start = start
+        self.increment = increment
+        self.optional = optional
+        if metadata is not None and schema is None and metadata.schema:
+            self.schema = schema = metadata.schema
+        else:
+            self.schema = quoted_name(schema, quote_schema)
+        self.metadata = metadata
+        self._key = _get_table_key(name, schema)
+        if metadata:
+            self._set_metadata(metadata)
+
+    @util.memoized_property
+    def is_callable(self):
+        return False
+
+    @util.memoized_property
+    def is_clause_element(self):
+        return False
+
+    @util.dependencies("sqlalchemy.sql.functions.func")
+    def next_value(self, func):
+        """Return a :class:`.next_value` function element
+        which will render the appropriate increment function
+        for this :class:`.Sequence` within any SQL expression.
+
+        """
+        return func.next_value(self, bind=self.bind)
+
+    def _set_parent(self, column):
+        super(Sequence, self)._set_parent(column)
+        column._on_table_attach(self._set_table)
+
+    def _set_table(self, column, table):
+        self._set_metadata(table.metadata)
+
+    def _set_metadata(self, metadata):
+        self.metadata = metadata
+        self.metadata._sequences[self._key] = self
+
+    @property
+    def bind(self):
+        if self.metadata:
+            return self.metadata.bind
+        else:
+            return None
+
+    def create(self, bind=None, checkfirst=True):
+        """Creates this sequence in the database."""
+
+        if bind is None:
+            bind = _bind_or_error(self)
+        bind._run_visitor(ddl.SchemaGenerator,
+                            self,
+                            checkfirst=checkfirst)
+
+    def drop(self, bind=None, checkfirst=True):
+        """Drops this sequence from the database."""
+
+        if bind is None:
+            bind = _bind_or_error(self)
+        bind._run_visitor(ddl.SchemaDropper,
+                            self,
+                            checkfirst=checkfirst)
+
+    def _not_a_column_expr(self):
+        raise exc.InvalidRequestError(
+                "This %s cannot be used directly "
+                "as a column expression.  Use func.next_value(sequence) "
+                "to produce a 'next value' function that's usable "
+                "as a column element."
+                % self.__class__.__name__)
+
+
+@inspection._self_inspects
+class FetchedValue(_NotAColumnExpr, SchemaEventTarget):
+    """A marker for a transparent database-side default.
+
+    Use :class:`.FetchedValue` when the database is configured
+    to provide some automatic default for a column.
+
+    E.g.::
+
+        Column('foo', Integer, FetchedValue())
+
+    Would indicate that some trigger or default generator
+    will create a new value for the ``foo`` column during an
+    INSERT.
+
+    .. seealso::
+
+        :ref:`triggered_columns`
+
+    """
+    is_server_default = True
+    reflected = False
+    has_argument = False
+
+    def __init__(self, for_update=False):
+        self.for_update = for_update
+
+    def _as_for_update(self, for_update):
+        if for_update == self.for_update:
+            return self
+        else:
+            return self._clone(for_update)
+
+    def _clone(self, for_update):
+        n = self.__class__.__new__(self.__class__)
+        n.__dict__.update(self.__dict__)
+        n.__dict__.pop('column', None)
+        n.for_update = for_update
+        return n
+
+    def _set_parent(self, column):
+        self.column = column
+        if self.for_update:
+            self.column.server_onupdate = self
+        else:
+            self.column.server_default = self
+
+    def __repr__(self):
+        return util.generic_repr(self)
+
+
+class DefaultClause(FetchedValue):
+    """A DDL-specified DEFAULT column value.
+
+    :class:`.DefaultClause` is a :class:`.FetchedValue`
+    that also generates a "DEFAULT" clause when
+    "CREATE TABLE" is emitted.
+
+    :class:`.DefaultClause` is generated automatically
+    whenever the ``server_default``, ``server_onupdate`` arguments of
+    :class:`.Column` are used.  A :class:`.DefaultClause`
+    can be passed positionally as well.
+
+    For example, the following::
+
+        Column('foo', Integer, server_default="50")
+
+    Is equivalent to::
+
+        Column('foo', Integer, DefaultClause("50"))
+
+    """
+
+    has_argument = True
+
+    def __init__(self, arg, for_update=False, _reflected=False):
+        util.assert_arg_type(arg, (util.string_types[0],
+                                   ClauseElement,
+                                   TextClause), 'arg')
+        super(DefaultClause, self).__init__(for_update)
+        self.arg = arg
+        self.reflected = _reflected
+
+    def __repr__(self):
+        return "DefaultClause(%r, for_update=%r)" % \
+                        (self.arg, self.for_update)
+
+
+class PassiveDefault(DefaultClause):
+    """A DDL-specified DEFAULT column value.
+
+    .. deprecated:: 0.6
+        :class:`.PassiveDefault` is deprecated.
+        Use :class:`.DefaultClause`.
+    """
+    @util.deprecated("0.6",
+                ":class:`.PassiveDefault` is deprecated.  "
+                "Use :class:`.DefaultClause`.",
+                False)
+    def __init__(self, *arg, **kw):
+        DefaultClause.__init__(self, *arg, **kw)
+
+
+class Constraint(DialectKWArgs, SchemaItem):
+    """A table-level SQL constraint."""
+
+    __visit_name__ = 'constraint'
+
+    def __init__(self, name=None, deferrable=None, initially=None,
+                            _create_rule=None,
+                            **dialect_kw):
+        """Create a SQL constraint.
+
+        :param name:
+          Optional, the in-database name of this ``Constraint``.
+
+        :param deferrable:
+          Optional bool.  If set, emit DEFERRABLE or NOT DEFERRABLE when
+          issuing DDL for this constraint.
+
+        :param initially:
+          Optional string.  If set, emit INITIALLY <value> when issuing DDL
+          for this constraint.
+
+        :param _create_rule:
+          a callable which is passed the DDLCompiler object during
+          compilation. Returns True or False to signal inline generation of
+          this Constraint.
+
+          The AddConstraint and DropConstraint DDL constructs provide
+          DDLElement's more comprehensive "conditional DDL" approach that is
+          passed a database connection when DDL is being issued. _create_rule
+          is instead called during any CREATE TABLE compilation, where there
+          may not be any transaction/connection in progress. However, it
+          allows conditional compilation of the constraint even for backends
+          which do not support addition of constraints through ALTER TABLE,
+          which currently includes SQLite.
+
+          _create_rule is used by some types to create constraints.
+          Currently, its call signature is subject to change at any time.
+
+        :param \**dialect_kw:  Additional keyword arguments are dialect specific,
+            and passed in the form ``<dialectname>_<argname>``.  See the
+            documentation regarding an individual dialect at :ref:`dialect_toplevel`
+            for detail on documented arguments.
+
+        """
+
+        self.name = name
+        self.deferrable = deferrable
+        self.initially = initially
+        self._create_rule = _create_rule
+        util.set_creation_order(self)
+        self._validate_dialect_kwargs(dialect_kw)
+
+    @property
+    def table(self):
+        try:
+            if isinstance(self.parent, Table):
+                return self.parent
+        except AttributeError:
+            pass
+        raise exc.InvalidRequestError(
+                    "This constraint is not bound to a table.  Did you "
+                    "mean to call table.append_constraint(constraint) ?")
+
+    def _set_parent(self, parent):
+        self.parent = parent
+        parent.constraints.add(self)
+
+    def copy(self, **kw):
+        raise NotImplementedError()
+
+
+def _to_schema_column(element):
+    if hasattr(element, '__clause_element__'):
+        element = element.__clause_element__()
+    if not isinstance(element, Column):
+        raise exc.ArgumentError("schema.Column object expected")
+    return element
+
+
+def _to_schema_column_or_string(element):
+    if hasattr(element, '__clause_element__'):
+        element = element.__clause_element__()
+    if not isinstance(element, util.string_types + (ColumnElement, )):
+        msg = "Element %r is not a string name or column element"
+        raise exc.ArgumentError(msg % element)
+    return element
+
+
+class ColumnCollectionMixin(object):
+    def __init__(self, *columns):
+        self.columns = ColumnCollection()
+        self._pending_colargs = [_to_schema_column_or_string(c)
+                                    for c in columns]
+        if self._pending_colargs and \
+                isinstance(self._pending_colargs[0], Column) and \
+                isinstance(self._pending_colargs[0].table, Table):
+            self._set_parent_with_dispatch(self._pending_colargs[0].table)
+
+    def _set_parent(self, table):
+        for col in self._pending_colargs:
+            if isinstance(col, util.string_types):
+                col = table.c[col]
+            self.columns.add(col)
+
+
+class ColumnCollectionConstraint(ColumnCollectionMixin, Constraint):
+    """A constraint that proxies a ColumnCollection."""
+
+    def __init__(self, *columns, **kw):
+        """
+        :param \*columns:
+          A sequence of column names or Column objects.
+
+        :param name:
+          Optional, the in-database name of this constraint.
+
+        :param deferrable:
+          Optional bool.  If set, emit DEFERRABLE or NOT DEFERRABLE when
+          issuing DDL for this constraint.
+
+        :param initially:
+          Optional string.  If set, emit INITIALLY <value> when issuing DDL
+          for this constraint.
+
+        :param \**kw: other keyword arguments including dialect-specific
+          arguments are propagated to the :class:`.Constraint` superclass.
+
+        """
+        ColumnCollectionMixin.__init__(self, *columns)
+        Constraint.__init__(self, **kw)
+
+    def _set_parent(self, table):
+        ColumnCollectionMixin._set_parent(self, table)
+        Constraint._set_parent(self, table)
+
+    def __contains__(self, x):
+        return x in self.columns
+
+    def copy(self, **kw):
+        c = self.__class__(name=self.name, deferrable=self.deferrable,
+                              initially=self.initially, *self.columns.keys())
+        return self._schema_item_copy(c)
+
+    def contains_column(self, col):
+        return self.columns.contains_column(col)
+
+    def __iter__(self):
+        # inlining of
+        # return iter(self.columns)
+        # ColumnCollection->OrderedProperties->OrderedDict
+        ordered_dict = self.columns._data
+        return (ordered_dict[key] for key in ordered_dict._list)
+
+    def __len__(self):
+        return len(self.columns._data)
+
+
+class CheckConstraint(Constraint):
+    """A table- or column-level CHECK constraint.
+
+    Can be included in the definition of a Table or Column.
+    """
+
+    def __init__(self, sqltext, name=None, deferrable=None,
+                    initially=None, table=None, _create_rule=None,
+                    _autoattach=True):
+        """Construct a CHECK constraint.
+
+        :param sqltext:
+          A string containing the constraint definition, which will be used
+          verbatim, or a SQL expression construct.   If given as a string,
+          the object is converted to a :class:`.Text` object.   If the textual
+          string includes a colon character, escape this using a backslash::
+
+            CheckConstraint(r"foo ~ E'a(?\:b|c)d")
+
+        :param name:
+          Optional, the in-database name of the constraint.
+
+        :param deferrable:
+          Optional bool.  If set, emit DEFERRABLE or NOT DEFERRABLE when
+          issuing DDL for this constraint.
+
+        :param initially:
+          Optional string.  If set, emit INITIALLY <value> when issuing DDL
+          for this constraint.
+
+        """
+
+        super(CheckConstraint, self).\
+                        __init__(name, deferrable, initially, _create_rule)
+        self.sqltext = _literal_as_text(sqltext)
+        if table is not None:
+            self._set_parent_with_dispatch(table)
+        elif _autoattach:
+            cols = _find_columns(self.sqltext)
+            tables = set([c.table for c in cols
+                        if isinstance(c.table, Table)])
+            if len(tables) == 1:
+                self._set_parent_with_dispatch(
+                        tables.pop())
+
+    def __visit_name__(self):
+        if isinstance(self.parent, Table):
+            return "check_constraint"
+        else:
+            return "column_check_constraint"
+    __visit_name__ = property(__visit_name__)
+
+    def copy(self, target_table=None, **kw):
+        if target_table is not None:
+            def replace(col):
+                if self.table.c.contains_column(col):
+                    return target_table.c[col.key]
+                else:
+                    return None
+            sqltext = visitors.replacement_traverse(self.sqltext, {}, replace)
+        else:
+            sqltext = self.sqltext
+        c = CheckConstraint(sqltext,
+                                name=self.name,
+                                initially=self.initially,
+                                deferrable=self.deferrable,
+                                _create_rule=self._create_rule,
+                                table=target_table,
+                                _autoattach=False)
+        return self._schema_item_copy(c)
+
+
+class ForeignKeyConstraint(Constraint):
+    """A table-level FOREIGN KEY constraint.
+
+    Defines a single column or composite FOREIGN KEY ... REFERENCES
+    constraint. For a no-frills, single column foreign key, adding a
+    :class:`.ForeignKey` to the definition of a :class:`.Column` is a shorthand
+    equivalent for an unnamed, single column :class:`.ForeignKeyConstraint`.
+
+    Examples of foreign key configuration are in :ref:`metadata_foreignkeys`.
+
+    """
+    __visit_name__ = 'foreign_key_constraint'
+
+    def __init__(self, columns, refcolumns, name=None, onupdate=None,
+            ondelete=None, deferrable=None, initially=None, use_alter=False,
+            link_to_name=False, match=None, table=None, **dialect_kw):
+        """Construct a composite-capable FOREIGN KEY.
+
+        :param columns: A sequence of local column names. The named columns
+          must be defined and present in the parent Table. The names should
+          match the ``key`` given to each column (defaults to the name) unless
+          ``link_to_name`` is True.
+
+        :param refcolumns: A sequence of foreign column names or Column
+          objects. The columns must all be located within the same Table.
+
+        :param name: Optional, the in-database name of the key.
+
+        :param onupdate: Optional string. If set, emit ON UPDATE <value> when
+          issuing DDL for this constraint. Typical values include CASCADE,
+          DELETE and RESTRICT.
+
+        :param ondelete: Optional string. If set, emit ON DELETE <value> when
+          issuing DDL for this constraint. Typical values include CASCADE,
+          DELETE and RESTRICT.
+
+        :param deferrable: Optional bool. If set, emit DEFERRABLE or NOT
+          DEFERRABLE when issuing DDL for this constraint.
+
+        :param initially: Optional string. If set, emit INITIALLY <value> when
+          issuing DDL for this constraint.
+
+        :param link_to_name: if True, the string name given in ``column`` is
+          the rendered name of the referenced column, not its locally assigned
+          ``key``.
+
+        :param use_alter: If True, do not emit the DDL for this constraint as
+          part of the CREATE TABLE definition. Instead, generate it via an
+          ALTER TABLE statement issued after the full collection of tables
+          have been created, and drop it via an ALTER TABLE statement before
+          the full collection of tables are dropped. This is shorthand for the
+          usage of :class:`.AddConstraint` and :class:`.DropConstraint` applied
+          as "after-create" and "before-drop" events on the MetaData object.
+          This is normally used to generate/drop constraints on objects that
+          are mutually dependent on each other.
+
+        :param match: Optional string. If set, emit MATCH <value> when issuing
+            DDL for this constraint. Typical values include SIMPLE, PARTIAL
+            and FULL.
+
+        :param \**dialect_kw:  Additional keyword arguments are dialect specific,
+            and passed in the form ``<dialectname>_<argname>``.  See the
+            documentation regarding an individual dialect at :ref:`dialect_toplevel`
+            for detail on documented arguments.
+
+            .. versionadded:: 0.9.2
+
+        """
+        super(ForeignKeyConstraint, self).\
+                        __init__(name, deferrable, initially, **dialect_kw)
+
+        self.onupdate = onupdate
+        self.ondelete = ondelete
+        self.link_to_name = link_to_name
+        if self.name is None and use_alter:
+            raise exc.ArgumentError("Alterable Constraint requires a name")
+        self.use_alter = use_alter
+        self.match = match
+
+        self._elements = util.OrderedDict()
+
+        # standalone ForeignKeyConstraint - create
+        # associated ForeignKey objects which will be applied to hosted
+        # Column objects (in col.foreign_keys), either now or when attached
+        # to the Table for string-specified names
+        for col, refcol in zip(columns, refcolumns):
+            self._elements[col] = ForeignKey(
+                    refcol,
+                    _constraint=self,
+                    name=self.name,
+                    onupdate=self.onupdate,
+                    ondelete=self.ondelete,
+                    use_alter=self.use_alter,
+                    link_to_name=self.link_to_name,
+                    match=self.match,
+                    deferrable=self.deferrable,
+                    initially=self.initially,
+                    **self.dialect_kwargs
+                )
+
+        if table is not None:
+            self._set_parent_with_dispatch(table)
+        elif columns and \
+            isinstance(columns[0], Column) and \
+                columns[0].table is not None:
+            self._set_parent_with_dispatch(columns[0].table)
+
+    def _validate_dest_table(self, table):
+        table_keys = set([elem._table_key() for elem in self._elements.values()])
+        if None not in table_keys and len(table_keys) > 1:
+            elem0, elem1 = sorted(table_keys)[0:2]
+            raise exc.ArgumentError(
+                'ForeignKeyConstraint on %s(%s) refers to '
+                'multiple remote tables: %s and %s' % (
+                table.fullname,
+                self._col_description,
+                elem0,
+                elem1
+            ))
+
+    @property
+    def _col_description(self):
+        return ", ".join(self._elements)
+
+    @property
+    def columns(self):
+        return list(self._elements)
+
+    @property
+    def elements(self):
+        return list(self._elements.values())
+
+    def _set_parent(self, table):
+        super(ForeignKeyConstraint, self)._set_parent(table)
+
+        self._validate_dest_table(table)
+
+        for col, fk in self._elements.items():
+            # string-specified column names now get
+            # resolved to Column objects
+            if isinstance(col, util.string_types):
+                try:
+                    col = table.c[col]
+                except KeyError:
+                    raise exc.ArgumentError(
+                        "Can't create ForeignKeyConstraint "
+                        "on table '%s': no column "
+                        "named '%s' is present." % (table.description, col))
+
+            if not hasattr(fk, 'parent') or \
+                    fk.parent is not col:
+                fk._set_parent_with_dispatch(col)
+
+        if self.use_alter:
+            def supports_alter(ddl, event, schema_item, bind, **kw):
+                return table in set(kw['tables']) and \
+                            bind.dialect.supports_alter
+
+            event.listen(table.metadata, "after_create",
+                         ddl.AddConstraint(self, on=supports_alter))
+            event.listen(table.metadata, "before_drop",
+                         ddl.DropConstraint(self, on=supports_alter))
+
+    def copy(self, schema=None, **kw):
+        fkc = ForeignKeyConstraint(
+                    [x.parent.key for x in self._elements.values()],
+                    [x._get_colspec(schema=schema) for x in self._elements.values()],
+                    name=self.name,
+                    onupdate=self.onupdate,
+                    ondelete=self.ondelete,
+                    use_alter=self.use_alter,
+                    deferrable=self.deferrable,
+                    initially=self.initially,
+                    link_to_name=self.link_to_name,
+                    match=self.match
+                )
+        for self_fk, other_fk in zip(
+                                self._elements.values(),
+                                fkc._elements.values()):
+            self_fk._schema_item_copy(other_fk)
+        return self._schema_item_copy(fkc)
+
+
+class PrimaryKeyConstraint(ColumnCollectionConstraint):
+    """A table-level PRIMARY KEY constraint.
+
+    The :class:`.PrimaryKeyConstraint` object is present automatically
+    on any :class:`.Table` object; it is assigned a set of
+    :class:`.Column` objects corresponding to those marked with
+    the :paramref:`.Column.primary_key` flag::
+
+        >>> my_table = Table('mytable', metadata,
+        ...                 Column('id', Integer, primary_key=True),
+        ...                 Column('version_id', Integer, primary_key=True),
+        ...                 Column('data', String(50))
+        ...     )
+        >>> my_table.primary_key
+        PrimaryKeyConstraint(
+            Column('id', Integer(), table=<mytable>, primary_key=True, nullable=False),
+            Column('version_id', Integer(), table=<mytable>, primary_key=True, nullable=False)
+        )
+
+    The primary key of a :class:`.Table` can also be specified by using
+    a :class:`.PrimaryKeyConstraint` object explicitly; in this mode of usage,
+    the "name" of the constraint can also be specified, as well as other
+    options which may be recognized by dialects::
+
+        my_table = Table('mytable', metadata,
+                    Column('id', Integer),
+                    Column('version_id', Integer),
+                    Column('data', String(50)),
+                    PrimaryKeyConstraint('id', 'version_id', name='mytable_pk')
+                )
+
+    The two styles of column-specification should generally not be mixed.
+    An warning is emitted if the columns present in the
+    :class:`.PrimaryKeyConstraint`
+    don't match the columns that were marked as ``primary_key=True``, if both
+    are present; in this case, the columns are taken strictly from the
+    :class:`.PrimaryKeyConstraint` declaration, and those columns otherwise marked
+    as ``primary_key=True`` are ignored.  This behavior is intended to be
+    backwards compatible with previous behavior.
+
+    .. versionchanged:: 0.9.2  Using a mixture of columns within a
+       :class:`.PrimaryKeyConstraint` in addition to columns marked as
+       ``primary_key=True`` now emits a warning if the lists don't match.
+       The ultimate behavior of ignoring those columns marked with the flag
+       only is currently maintained for backwards compatibility; this warning
+       may raise an exception in a future release.
+
+    For the use case where specific options are to be specified on the
+    :class:`.PrimaryKeyConstraint`, but the usual style of using ``primary_key=True``
+    flags is still desirable, an empty :class:`.PrimaryKeyConstraint` may be
+    specified, which will take on the primary key column collection from
+    the :class:`.Table` based on the flags::
+
+        my_table = Table('mytable', metadata,
+                    Column('id', Integer, primary_key=True),
+                    Column('version_id', Integer, primary_key=True),
+                    Column('data', String(50)),
+                    PrimaryKeyConstraint(name='mytable_pk', mssql_clustered=True)
+                )
+
+    .. versionadded:: 0.9.2 an empty :class:`.PrimaryKeyConstraint` may now
+       be specified for the purposes of establishing keyword arguments with the
+       constraint, independently of the specification of "primary key" columns
+       within the :class:`.Table` itself; columns marked as ``primary_key=True``
+       will be gathered into the empty constraint's column collection.
+
+    """
+
+    __visit_name__ = 'primary_key_constraint'
+
+    def _set_parent(self, table):
+        super(PrimaryKeyConstraint, self)._set_parent(table)
+
+        if table.primary_key is not self:
+            table.constraints.discard(table.primary_key)
+            table.primary_key = self
+            table.constraints.add(self)
+
+        table_pks = [c for c in table.c if c.primary_key]
+        if self.columns and table_pks and \
+            set(table_pks) != set(self.columns.values()):
+            util.warn(
+                    "Table '%s' specifies columns %s as primary_key=True, "
+                    "not matching locally specified columns %s; setting the "
+                    "current primary key columns to %s. This warning "
+                    "may become an exception in a future release" %
+                    (
+                        table.name,
+                        ", ".join("'%s'" % c.name for c in table_pks),
+                        ", ".join("'%s'" % c.name for c in self.columns),
+                        ", ".join("'%s'" % c.name for c in self.columns)
+                    )
+                )
+            table_pks[:] = []
+
+        for c in self.columns:
+            c.primary_key = True
+        self.columns.extend(table_pks)
+
+    def _reload(self, columns):
+        """repopulate this :class:`.PrimaryKeyConstraint` given
+        a set of columns.
+
+        Existing columns in the table that are marked as primary_key=True
+        are maintained.
+
+        Also fires a new event.
+
+        This is basically like putting a whole new
+        :class:`.PrimaryKeyConstraint` object on the parent
+        :class:`.Table` object without actually replacing the object.
+
+        The ordering of the given list of columns is also maintained; these
+        columns will be appended to the list of columns after any which
+        are already present.
+
+        """
+
+        # set the primary key flag on new columns.
+        # note any existing PK cols on the table also have their
+        # flag still set.
+        for col in columns:
+            col.primary_key = True
+
+        self.columns.extend(columns)
+
+        self._set_parent_with_dispatch(self.table)
+
+    def _replace(self, col):
+        self.columns.replace(col)
+
+
+class UniqueConstraint(ColumnCollectionConstraint):
+    """A table-level UNIQUE constraint.
+
+    Defines a single column or composite UNIQUE constraint. For a no-frills,
+    single column constraint, adding ``unique=True`` to the ``Column``
+    definition is a shorthand equivalent for an unnamed, single column
+    UniqueConstraint.
+    """
+
+    __visit_name__ = 'unique_constraint'
+
+
+class Index(DialectKWArgs, ColumnCollectionMixin, SchemaItem):
+    """A table-level INDEX.
+
+    Defines a composite (one or more column) INDEX.
+
+    E.g.::
+
+        sometable = Table("sometable", metadata,
+                        Column("name", String(50)),
+                        Column("address", String(100))
+                    )
+
+        Index("some_index", sometable.c.name)
+
+    For a no-frills, single column index, adding
+    :class:`.Column` also supports ``index=True``::
+
+        sometable = Table("sometable", metadata,
+                        Column("name", String(50), index=True)
+                    )
+
+    For a composite index, multiple columns can be specified::
+
+        Index("some_index", sometable.c.name, sometable.c.address)
+
+    Functional indexes are supported as well, keeping in mind that at least
+    one :class:`.Column` must be present::
+
+        Index("some_index", func.lower(sometable.c.name))
+
+    .. versionadded:: 0.8 support for functional and expression-based indexes.
+
+    .. seealso::
+
+        :ref:`schema_indexes` - General information on :class:`.Index`.
+
+        :ref:`postgresql_indexes` - PostgreSQL-specific options available for the
+        :class:`.Index` construct.
+
+        :ref:`mysql_indexes` - MySQL-specific options available for the
+        :class:`.Index` construct.
+
+        :ref:`mssql_indexes` - MSSQL-specific options available for the
+        :class:`.Index` construct.
+
+    """
+
+    __visit_name__ = 'index'
+
+    def __init__(self, name, *expressions, **kw):
+        """Construct an index object.
+
+        :param name:
+          The name of the index
+
+        :param \*expressions:
+          Column expressions to include in the index.   The expressions
+          are normally instances of :class:`.Column`, but may also
+          be arbitrary SQL expressions which ultmately refer to a
+          :class:`.Column`.
+
+        :param unique=False:
+            Keyword only argument; if True, create a unique index.
+
+        :param quote=None:
+            Keyword only argument; whether to apply quoting to the name of
+            the index.  Works in the same manner as that of
+            :paramref:`.Column.quote`.
+
+        :param \**kw: Additional keyword arguments not mentioned above are
+            dialect specific, and passed in the form ``<dialectname>_<argname>``.
+            See the documentation regarding an individual dialect at
+            :ref:`dialect_toplevel` for detail on documented arguments.
+
+        """
+        self.table = None
+
+        columns = []
+        for expr in expressions:
+            if not isinstance(expr, ClauseElement):
+                columns.append(expr)
+            else:
+                cols = []
+                visitors.traverse(expr, {}, {'column': cols.append})
+                if cols:
+                    columns.append(cols[0])
+                else:
+                    columns.append(expr)
+
+        self.expressions = expressions
+        self.name = quoted_name(name, kw.pop("quote", None))
+        self.unique = kw.pop('unique', False)
+        self._validate_dialect_kwargs(kw)
+
+        # will call _set_parent() if table-bound column
+        # objects are present
+        ColumnCollectionMixin.__init__(self, *columns)
+
+
+
+    def _set_parent(self, table):
+        ColumnCollectionMixin._set_parent(self, table)
+
+        if self.table is not None and table is not self.table:
+            raise exc.ArgumentError(
+                "Index '%s' is against table '%s', and "
+                "cannot be associated with table '%s'." % (
+                    self.name,
+                    self.table.description,
+                    table.description
+                )
+            )
+        self.table = table
+        for c in self.columns:
+            if c.table != self.table:
+                raise exc.ArgumentError(
+                    "Column '%s' is not part of table '%s'." %
+                    (c, self.table.description)
+                )
+        table.indexes.add(self)
+
+        self.expressions = [
+            expr if isinstance(expr, ClauseElement)
+            else colexpr
+            for expr, colexpr in zip(self.expressions, self.columns)
+        ]
+
+    @property
+    def bind(self):
+        """Return the connectable associated with this Index."""
+
+        return self.table.bind
+
+    def create(self, bind=None):
+        """Issue a ``CREATE`` statement for this
+        :class:`.Index`, using the given :class:`.Connectable`
+        for connectivity.
+
+        .. seealso::
+
+            :meth:`.MetaData.create_all`.
+
+        """
+        if bind is None:
+            bind = _bind_or_error(self)
+        bind._run_visitor(ddl.SchemaGenerator, self)
+        return self
+
+    def drop(self, bind=None):
+        """Issue a ``DROP`` statement for this
+        :class:`.Index`, using the given :class:`.Connectable`
+        for connectivity.
+
+        .. seealso::
+
+            :meth:`.MetaData.drop_all`.
+
+        """
+        if bind is None:
+            bind = _bind_or_error(self)
+        bind._run_visitor(ddl.SchemaDropper, self)
+
+    def __repr__(self):
+        return 'Index(%s)' % (
+                    ", ".join(
+                        [repr(self.name)] +
+                        [repr(c) for c in self.columns] +
+                        (self.unique and ["unique=True"] or [])
+                    ))
+
+
+class MetaData(SchemaItem):
+    """A collection of :class:`.Table` objects and their associated schema
+    constructs.
+
+    Holds a collection of :class:`.Table` objects as well as
+    an optional binding to an :class:`.Engine` or
+    :class:`.Connection`.  If bound, the :class:`.Table` objects
+    in the collection and their columns may participate in implicit SQL
+    execution.
+
+    The :class:`.Table` objects themselves are stored in the
+    :attr:`.MetaData.tables` dictionary.
+
+    :class:`.MetaData` is a thread-safe object for read operations.  Construction
+    of new tables within a single :class:`.MetaData` object, either explicitly
+    or via reflection, may not be completely thread-safe.
+
+    .. seealso::
+
+        :ref:`metadata_describing` - Introduction to database metadata
+
+    """
+
+    __visit_name__ = 'metadata'
+
+    def __init__(self, bind=None, reflect=False, schema=None,
+                 quote_schema=None):
+        """Create a new MetaData object.
+
+        :param bind:
+          An Engine or Connection to bind to.  May also be a string or URL
+          instance, these are passed to create_engine() and this MetaData will
+          be bound to the resulting engine.
+
+        :param reflect:
+          Optional, automatically load all tables from the bound database.
+          Defaults to False. ``bind`` is required when this option is set.
+
+          .. deprecated:: 0.8
+                Please use the :meth:`.MetaData.reflect` method.
+
+        :param schema:
+           The default schema to use for the :class:`.Table`,
+           :class:`.Sequence`, and other objects associated with this
+           :class:`.MetaData`. Defaults to ``None``.
+
+        :param quote_schema:
+            Sets the ``quote_schema`` flag for those :class:`.Table`,
+            :class:`.Sequence`, and other objects which make usage of the
+            local ``schema`` name.
+
+        .. versionadded:: 0.7.4
+            ``schema`` and ``quote_schema`` parameters.
+
+        """
+        self.tables = util.immutabledict()
+        self.schema = quoted_name(schema, quote_schema)
+        self._schemas = set()
+        self._sequences = {}
+        self._fk_memos = collections.defaultdict(list)
+
+        self.bind = bind
+        if reflect:
+            util.warn("reflect=True is deprecate; please "
+                            "use the reflect() method.")
+            if not bind:
+                raise exc.ArgumentError(
+                    "A bind must be supplied in conjunction "
+                    "with reflect=True")
+            self.reflect()
+
+    tables = None
+    """A dictionary of :class:`.Table` objects keyed to their name or "table key".
+
+    The exact key is that determined by the :attr:`.Table.key` attribute;
+    for a table with no :attr:`.Table.schema` attribute, this is the same
+    as :attr:`.Table.name`.  For a table with a schema, it is typically of the
+    form ``schemaname.tablename``.
+
+    .. seealso::
+
+        :attr:`.MetaData.sorted_tables`
+
+    """
+
+    def __repr__(self):
+        return 'MetaData(bind=%r)' % self.bind
+
+    def __contains__(self, table_or_key):
+        if not isinstance(table_or_key, util.string_types):
+            table_or_key = table_or_key.key
+        return table_or_key in self.tables
+
+    def _add_table(self, name, schema, table):
+        key = _get_table_key(name, schema)
+        dict.__setitem__(self.tables, key, table)
+        if schema:
+            self._schemas.add(schema)
+
+
+
+    def _remove_table(self, name, schema):
+        key = _get_table_key(name, schema)
+        removed = dict.pop(self.tables, key, None)
+        if removed is not None:
+            for fk in removed.foreign_keys:
+                fk._remove_from_metadata(self)
+        if self._schemas:
+            self._schemas = set([t.schema
+                                for t in self.tables.values()
+                                if t.schema is not None])
+
+
+    def __getstate__(self):
+        return {'tables': self.tables,
+                'schema': self.schema,
+                'schemas': self._schemas,
+                'sequences': self._sequences,
+                'fk_memos': self._fk_memos}
+
+    def __setstate__(self, state):
+        self.tables = state['tables']
+        self.schema = state['schema']
+        self._bind = None
+        self._sequences = state['sequences']
+        self._schemas = state['schemas']
+        self._fk_memos = state['fk_memos']
+
+    def is_bound(self):
+        """True if this MetaData is bound to an Engine or Connection."""
+
+        return self._bind is not None
+
+    def bind(self):
+        """An :class:`.Engine` or :class:`.Connection` to which this
+        :class:`.MetaData` is bound.
+
+        Typically, a :class:`.Engine` is assigned to this attribute
+        so that "implicit execution" may be used, or alternatively
+        as a means of providing engine binding information to an
+        ORM :class:`.Session` object::
+
+            engine = create_engine("someurl://")
+            metadata.bind = engine
+
+        .. seealso::
+
+           :ref:`dbengine_implicit` - background on "bound metadata"
+
+        """
+        return self._bind
+
+    @util.dependencies("sqlalchemy.engine.url")
+    def _bind_to(self, url, bind):
+        """Bind this MetaData to an Engine, Connection, string or URL."""
+
+        if isinstance(bind, util.string_types + (url.URL, )):
+            self._bind = sqlalchemy.create_engine(bind)
+        else:
+            self._bind = bind
+    bind = property(bind, _bind_to)
+
+    def clear(self):
+        """Clear all Table objects from this MetaData."""
+
+        dict.clear(self.tables)
+        self._schemas.clear()
+        self._fk_memos.clear()
+
+    def remove(self, table):
+        """Remove the given Table object from this MetaData."""
+
+        self._remove_table(table.name, table.schema)
+
+    @property
+    def sorted_tables(self):
+        """Returns a list of :class:`.Table` objects sorted in order of
+        foreign key dependency.
+
+        The sorting will place :class:`.Table` objects that have dependencies
+        first, before the dependencies themselves, representing the
+        order in which they can be created.   To get the order in which
+        the tables would be dropped, use the ``reversed()`` Python built-in.
+
+        .. seealso::
+
+            :attr:`.MetaData.tables`
+
+            :meth:`.Inspector.get_table_names`
+
+        """
+        return ddl.sort_tables(self.tables.values())
+
+    def reflect(self, bind=None, schema=None, views=False, only=None,
+                                extend_existing=False,
+                                autoload_replace=True):
+        """Load all available table definitions from the database.
+
+        Automatically creates ``Table`` entries in this ``MetaData`` for any
+        table available in the database but not yet present in the
+        ``MetaData``.  May be called multiple times to pick up tables recently
+        added to the database, however no special action is taken if a table
+        in this ``MetaData`` no longer exists in the database.
+
+        :param bind:
+          A :class:`.Connectable` used to access the database; if None, uses
+          the existing bind on this ``MetaData``, if any.
+
+        :param schema:
+          Optional, query and reflect tables from an alterate schema.
+          If None, the schema associated with this :class:`.MetaData`
+          is used, if any.
+
+        :param views:
+          If True, also reflect views.
+
+        :param only:
+          Optional.  Load only a sub-set of available named tables.  May be
+          specified as a sequence of names or a callable.
+
+          If a sequence of names is provided, only those tables will be
+          reflected.  An error is raised if a table is requested but not
+          available.  Named tables already present in this ``MetaData`` are
+          ignored.
+
+          If a callable is provided, it will be used as a boolean predicate to
+          filter the list of potential table names.  The callable is called
+          with a table name and this ``MetaData`` instance as positional
+          arguments and should return a true value for any table to reflect.
+
+        :param extend_existing: Passed along to each :class:`.Table` as
+          :paramref:`.Table.extend_existing`.
+
+          .. versionadded:: 0.9.1
+
+        :param autoload_replace: Passed along to each :class:`.Table` as
+          :paramref:`.Table.autoload_replace`.
+
+          .. versionadded:: 0.9.1
+
+
+        """
+        if bind is None:
+            bind = _bind_or_error(self)
+
+        with bind.connect() as conn:
+
+            reflect_opts = {
+                'autoload': True,
+                'autoload_with': conn,
+                'extend_existing': extend_existing,
+                'autoload_replace': autoload_replace
+            }
+
+            if schema is None:
+                schema = self.schema
+
+            if schema is not None:
+                reflect_opts['schema'] = schema
+
+            available = util.OrderedSet(bind.engine.table_names(schema,
+                                                            connection=conn))
+            if views:
+                available.update(
+                    bind.dialect.get_view_names(conn, schema)
+                )
+
+            if schema is not None:
+                available_w_schema = util.OrderedSet(["%s.%s" % (schema, name)
+                                        for name in available])
+            else:
+                available_w_schema = available
+
+            current = set(self.tables)
+
+            if only is None:
+                load = [name for name, schname in
+                        zip(available, available_w_schema)
+                        if extend_existing or schname not in current]
+            elif util.callable(only):
+                load = [name for name, schname in
+                            zip(available, available_w_schema)
+                            if (extend_existing or schname not in current)
+                            and only(name, self)]
+            else:
+                missing = [name for name in only if name not in available]
+                if missing:
+                    s = schema and (" schema '%s'" % schema) or ''
+                    raise exc.InvalidRequestError(
+                        'Could not reflect: requested table(s) not available '
+                        'in %s%s: (%s)' %
+                        (bind.engine.url, s, ', '.join(missing)))
+                load = [name for name in only if extend_existing or
+                                                    name not in current]
+
+            for name in load:
+                Table(name, self, **reflect_opts)
+
+    def append_ddl_listener(self, event_name, listener):
+        """Append a DDL event listener to this ``MetaData``.
+
+        .. deprecated:: 0.7
+            See :class:`.DDLEvents`.
+
+        """
+        def adapt_listener(target, connection, **kw):
+            tables = kw['tables']
+            listener(event, target, connection, tables=tables)
+
+        event.listen(self, "" + event_name.replace('-', '_'), adapt_listener)
+
+    def create_all(self, bind=None, tables=None, checkfirst=True):
+        """Create all tables stored in this metadata.
+
+        Conditional by default, will not attempt to recreate tables already
+        present in the target database.
+
+        :param bind:
+          A :class:`.Connectable` used to access the
+          database; if None, uses the existing bind on this ``MetaData``, if
+          any.
+
+        :param tables:
+          Optional list of ``Table`` objects, which is a subset of the total
+          tables in the ``MetaData`` (others are ignored).
+
+        :param checkfirst:
+          Defaults to True, don't issue CREATEs for tables already present
+          in the target database.
+
+        """
+        if bind is None:
+            bind = _bind_or_error(self)
+        bind._run_visitor(ddl.SchemaGenerator,
+                            self,
+                            checkfirst=checkfirst,
+                            tables=tables)
+
+    def drop_all(self, bind=None, tables=None, checkfirst=True):
+        """Drop all tables stored in this metadata.
+
+        Conditional by default, will not attempt to drop tables not present in
+        the target database.
+
+        :param bind:
+          A :class:`.Connectable` used to access the
+          database; if None, uses the existing bind on this ``MetaData``, if
+          any.
+
+        :param tables:
+          Optional list of ``Table`` objects, which is a subset of the
+          total tables in the ``MetaData`` (others are ignored).
+
+        :param checkfirst:
+          Defaults to True, only issue DROPs for tables confirmed to be
+          present in the target database.
+
+        """
+        if bind is None:
+            bind = _bind_or_error(self)
+        bind._run_visitor(ddl.SchemaDropper,
+                            self,
+                            checkfirst=checkfirst,
+                            tables=tables)
+
+
+class ThreadLocalMetaData(MetaData):
+    """A MetaData variant that presents a different ``bind`` in every thread.
+
+    Makes the ``bind`` property of the MetaData a thread-local value, allowing
+    this collection of tables to be bound to different ``Engine``
+    implementations or connections in each thread.
+
+    The ThreadLocalMetaData starts off bound to None in each thread.  Binds
+    must be made explicitly by assigning to the ``bind`` property or using
+    ``connect()``.  You can also re-bind dynamically multiple times per
+    thread, just like a regular ``MetaData``.
+
+    """
+
+    __visit_name__ = 'metadata'
+
+    def __init__(self):
+        """Construct a ThreadLocalMetaData."""
+
+        self.context = util.threading.local()
+        self.__engines = {}
+        super(ThreadLocalMetaData, self).__init__()
+
+    def bind(self):
+        """The bound Engine or Connection for this thread.
+
+        This property may be assigned an Engine or Connection, or assigned a
+        string or URL to automatically create a basic Engine for this bind
+        with ``create_engine()``."""
+
+        return getattr(self.context, '_engine', None)
+
+    @util.dependencies("sqlalchemy.engine.url")
+    def _bind_to(self, url, bind):
+        """Bind to a Connectable in the caller's thread."""
+
+        if isinstance(bind, util.string_types + (url.URL, )):
+            try:
+                self.context._engine = self.__engines[bind]
+            except KeyError:
+                e = sqlalchemy.create_engine(bind)
+                self.__engines[bind] = e
+                self.context._engine = e
+        else:
+            # TODO: this is squirrely.  we shouldnt have to hold onto engines
+            # in a case like this
+            if bind not in self.__engines:
+                self.__engines[bind] = bind
+            self.context._engine = bind
+
+    bind = property(bind, _bind_to)
+
+    def is_bound(self):
+        """True if there is a bind for this thread."""
+        return (hasattr(self.context, '_engine') and
+                self.context._engine is not None)
+
+    def dispose(self):
+        """Dispose all bound engines, in all thread contexts."""
+
+        for e in self.__engines.values():
+            if hasattr(e, 'dispose'):
+                e.dispose()
+
+
+