diff options
Diffstat (limited to 'lib/sqlalchemy/sql/schema.py')
| -rw-r--r-- | lib/sqlalchemy/sql/schema.py | 95 |
1 files changed, 78 insertions, 17 deletions
diff --git a/lib/sqlalchemy/sql/schema.py b/lib/sqlalchemy/sql/schema.py index b90f7fc53..65a1da877 100644 --- a/lib/sqlalchemy/sql/schema.py +++ b/lib/sqlalchemy/sql/schema.py @@ -516,6 +516,19 @@ class Table(DialectKWArgs, SchemaItem, TableClause): """ return sorted(self.constraints, key=lambda c: c._creation_order) + @property + def foreign_key_constraints(self): + """:class:`.ForeignKeyConstraint` objects referred to by this + :class:`.Table`. + + This list is produced from the collection of :class:`.ForeignKey` + objects currently associated. + + .. versionadded:: 1.0.0 + + """ + return set(fkc.constraint for fkc in self.foreign_keys) + def _init_existing(self, *args, **kwargs): autoload_with = kwargs.pop('autoload_with', None) autoload = kwargs.pop('autoload', autoload_with is not None) @@ -1463,7 +1476,14 @@ class ForeignKey(DialectKWArgs, SchemaItem): :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. + statement. See :paramref:`.ForeignKeyConstraint.use_alter` + for further description. + + .. seealso:: + + :paramref:`.ForeignKeyConstraint.use_alter` + + :ref:`use_alter` :param match: Optional string. If set, emit MATCH <value> when issuing DDL for this constraint. Typical values include SIMPLE, PARTIAL @@ -2345,6 +2365,14 @@ def _to_schema_column_or_string(element): class ColumnCollectionMixin(object): + columns = None + """A :class:`.ColumnCollection` of :class:`.Column` objects. + + This collection represents the columns which are referred to by + this object. + + """ + def __init__(self, *columns): self.columns = ColumnCollection() self._pending_colargs = [_to_schema_column_or_string(c) @@ -2545,11 +2573,23 @@ class ForeignKeyConstraint(ColumnCollectionConstraint): 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. + the full collection of tables are dropped. + + The use of :paramref:`.ForeignKeyConstraint.use_alter` is + particularly geared towards the case where two or more tables + are established within a mutually-dependent foreign key constraint + relationship; however, the :meth:`.MetaData.create_all` and + :meth:`.MetaData.drop_all` methods will perform this resolution + automatically, so the flag is normally not needed. + + .. versionchanged:: 1.0.0 Automatic resolution of foreign key + cycles has been added, removing the need to use the + :paramref:`.ForeignKeyConstraint.use_alter` in typical use + cases. + + .. seealso:: + + :ref:`use_alter` :param match: Optional string. If set, emit MATCH <value> when issuing DDL for this constraint. Typical values include SIMPLE, PARTIAL @@ -2575,8 +2615,6 @@ class ForeignKeyConstraint(ColumnCollectionConstraint): 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 @@ -2624,6 +2662,20 @@ class ForeignKeyConstraint(ColumnCollectionConstraint): else: return None + @property + def referred_table(self): + """The :class:`.Table` object to which this + :class:`.ForeignKeyConstraint` references. + + This is a dynamically calculated attribute which may not be available + if the constraint and/or parent table is not yet associated with + a metadata collection that contains the referred table. + + .. versionadded:: 1.0.0 + + """ + return self.elements[0].column.table + def _validate_dest_table(self, table): table_keys = set([elem._table_key() for elem in self.elements]) @@ -2681,15 +2733,6 @@ class ForeignKeyConstraint(ColumnCollectionConstraint): self._validate_dest_table(table) - 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, target_table=None, **kw): fkc = ForeignKeyConstraint( @@ -3333,12 +3376,30 @@ class MetaData(SchemaItem): order in which they can be created. To get the order in which the tables would be dropped, use the ``reversed()`` Python built-in. + .. warning:: + + The :attr:`.sorted_tables` accessor cannot by itself accommodate + automatic resolution of dependency cycles between tables, which + are usually caused by mutually dependent foreign key constraints. + To resolve these cycles, either the + :paramref:`.ForeignKeyConstraint.use_alter` parameter may be appled + to those constraints, or use the + :func:`.schema.sort_tables_and_constraints` function which will break + out foreign key constraints involved in cycles separately. + .. seealso:: + :func:`.schema.sort_tables` + + :func:`.schema.sort_tables_and_constraints` + :attr:`.MetaData.tables` :meth:`.Inspector.get_table_names` + :meth:`.Inspector.get_sorted_table_and_fkc_names` + + """ return ddl.sort_tables(self.tables.values()) |