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diff --git a/lib/sqlalchemy/ext/automap.py b/lib/sqlalchemy/ext/automap.py new file mode 100644 index 000000000..7a1512f6a --- /dev/null +++ b/lib/sqlalchemy/ext/automap.py @@ -0,0 +1,840 @@ +# ext/automap.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 + +"""Define an extension to the :mod:`sqlalchemy.ext.declarative` system +which automatically generates mapped classes and relationships from a database +schema, typically though not necessarily one which is reflected. + +.. versionadded:: 0.9.1 Added :mod:`sqlalchemy.ext.automap`. + +.. note:: + + The :mod:`sqlalchemy.ext.automap` extension should be considered + **experimental** as of 0.9.1. Featureset and API stability is + not guaranteed at this time. + +It is hoped that the :class:`.AutomapBase` system provides a quick +and modernized solution to the problem that the very famous +`SQLSoup <https://sqlsoup.readthedocs.org/en/latest/>`_ +also tries to solve, that of generating a quick and rudimentary object +model from an existing database on the fly. By addressing the issue strictly +at the mapper configuration level, and integrating fully with existing +Declarative class techniques, :class:`.AutomapBase` seeks to provide +a well-integrated approach to the issue of expediently auto-generating ad-hoc +mappings. + + +Basic Use +========= + +The simplest usage is to reflect an existing database into a new model. +We create a new :class:`.AutomapBase` class in a similar manner as to how +we create a declarative base class, using :func:`.automap_base`. +We then call :meth:`.AutomapBase.prepare` on the resulting base class, +asking it to reflect the schema and produce mappings:: + + from sqlalchemy.ext.automap import automap_base + from sqlalchemy.orm import Session + from sqlalchemy import create_engine + + Base = automap_base() + + # engine, suppose it has two tables 'user' and 'address' set up + engine = create_engine("sqlite:///mydatabase.db") + + # reflect the tables + Base.prepare(engine, reflect=True) + + # mapped classes are now created with names by default + # matching that of the table name. + User = Base.classes.user + Address = Base.classes.address + + session = Session(engine) + + # rudimentary relationships are produced + session.add(Address(email_address="foo@bar.com", user=User(name="foo"))) + session.commit() + + # collection-based relationships are by default named "<classname>_collection" + print (u1.address_collection) + +Above, calling :meth:`.AutomapBase.prepare` while passing along the +:paramref:`.AutomapBase.prepare.reflect` parameter indicates that the +:meth:`.MetaData.reflect` method will be called on this declarative base +classes' :class:`.MetaData` collection; then, each viable +:class:`.Table` within the :class:`.MetaData` will get a new mapped class +generated automatically. The :class:`.ForeignKeyConstraint` objects which +link the various tables together will be used to produce new, bidirectional +:func:`.relationship` objects between classes. The classes and relationships +follow along a default naming scheme that we can customize. At this point, +our basic mapping consisting of related ``User`` and ``Address`` classes is ready +to use in the traditional way. + +Generating Mappings from an Existing MetaData +============================================= + +We can pass a pre-declared :class:`.MetaData` object to :func:`.automap_base`. +This object can be constructed in any way, including programmatically, from +a serialized file, or from itself being reflected using :meth:`.MetaData.reflect`. +Below we illustrate a combination of reflection and explicit table declaration:: + + from sqlalchemy import create_engine, MetaData, Table, Column, ForeignKey + engine = create_engine("sqlite:///mydatabase.db") + + # produce our own MetaData object + metadata = MetaData() + + # we can reflect it ourselves from a database, using options + # such as 'only' to limit what tables we look at... + metadata.reflect(engine, only=['user', 'address']) + + # ... or just define our own Table objects with it (or combine both) + Table('user_order', metadata, + Column('id', Integer, primary_key=True), + Column('user_id', ForeignKey('user.id')) + ) + + # we can then produce a set of mappings from this MetaData. + Base = automap_base(metadata=metadata) + + # calling prepare() just sets up mapped classes and relationships. + Base.prepare() + + # mapped classes are ready + User, Address, Order = Base.classes.user, Base.classes.address, Base.classes.user_order + +Specifying Classes Explcitly +============================ + +The :mod:`.sqlalchemy.ext.automap` extension allows classes to be defined +explicitly, in a way similar to that of the :class:`.DeferredReflection` class. +Classes that extend from :class:`.AutomapBase` act like regular declarative +classes, but are not immediately mapped after their construction, and are instead +mapped when we call :meth:`.AutomapBase.prepare`. The :meth:`.AutomapBase.prepare` +method will make use of the classes we've established based on the table name +we use. If our schema contains tables ``user`` and ``address``, we can define +one or both of the classes to be used:: + + from sqlalchemy.ext.automap import automap_base + from sqlalchemy import create_engine + + # automap base + Base = automap_base() + + # pre-declare User for the 'user' table + class User(Base): + __tablename__ = 'user' + + # override schema elements like Columns + user_name = Column('name', String) + + # override relationships too, if desired. + # we must use the same name that automap would use for the relationship, + # and also must refer to the class name that automap will generate + # for "address" + address_collection = relationship("address", collection_class=set) + + # reflect + engine = create_engine("sqlite:///mydatabase.db") + Base.prepare(engine, reflect=True) + + # we still have Address generated from the tablename "address", + # but User is the same as Base.classes.User now + + Address = Base.classes.address + + u1 = session.query(User).first() + print (u1.address_collection) + + # the backref is still there: + a1 = session.query(Address).first() + print (a1.user) + +Above, one of the more intricate details is that we illustrated overriding +one of the :func:`.relationship` objects that automap would have created. +To do this, we needed to make sure the names match up with what automap +would normally generate, in that the relationship name would be ``User.address_collection`` +and the name of the class referred to, from automap's perspective, is called +``address``, even though we are referring to it as ``Address`` within our usage +of this class. + +Overriding Naming Schemes +========================= + +:mod:`.sqlalchemy.ext.automap` is tasked with producing mapped classes and +relationship names based on a schema, which means it has decision points in how +these names are determined. These three decision points are provided using +functions which can be passed to the :meth:`.AutomapBase.prepare` method, and +are known as :func:`.classname_for_table`, +:func:`.name_for_scalar_relationship`, +and :func:`.name_for_collection_relationship`. Any or all of these +functions are provided as in the example below, where we use a "camel case" +scheme for class names and a "pluralizer" for collection names using the +`Inflect <https://pypi.python.org/pypi/inflect>`_ package:: + + import re + import inflect + + def camelize_classname(base, tablename, table): + "Produce a 'camelized' class name, e.g. " + "'words_and_underscores' -> 'WordsAndUnderscores'" + + return str(tablename[0].upper() + \\ + re.sub(r'_(\w)', lambda m: m.group(1).upper(), tablename[1:])) + + _pluralizer = inflect.engine() + def pluralize_collection(base, local_cls, referred_cls, constraint): + "Produce an 'uncamelized', 'pluralized' class name, e.g. " + "'SomeTerm' -> 'some_terms'" + + referred_name = referred_cls.__name__ + uncamelized = referred_name[0].lower() + \\ + re.sub(r'\W', + lambda m: "_%s" % m.group(0).lower(), + referred_name[1:]) + pluralized = _pluralizer.plural(uncamelized) + return pluralized + + from sqlalchemy.ext.automap import automap_base + + Base = automap_base() + + engine = create_engine("sqlite:///mydatabase.db") + + Base.prepare(engine, reflect=True, + classname_for_table=camelize_classname, + name_for_collection_relationship=pluralize_collection + ) + +From the above mapping, we would now have classes ``User`` and ``Address``, +where the collection from ``User`` to ``Address`` is called ``User.addresses``:: + + User, Address = Base.classes.User, Base.classes.Address + + u1 = User(addresses=[Address(email="foo@bar.com")]) + +Relationship Detection +====================== + +The vast majority of what automap accomplishes is the generation of +:func:`.relationship` structures based on foreign keys. The mechanism +by which this works for many-to-one and one-to-many relationships is as follows: + +1. A given :class:`.Table`, known to be mapped to a particular class, + is examined for :class:`.ForeignKeyConstraint` objects. + +2. From each :class:`.ForeignKeyConstraint`, the remote :class:`.Table` + object present is matched up to the class to which it is to be mapped, + if any, else it is skipped. + +3. As the :class:`.ForeignKeyConstraint` we are examining correponds to a reference + from the immediate mapped class, + the relationship will be set up as a many-to-one referring to the referred class; + a corresponding one-to-many backref will be created on the referred class referring + to this class. + +4. The names of the relationships are determined using the + :paramref:`.AutomapBase.prepare.name_for_scalar_relationship` and + :paramref:`.AutomapBase.prepare.name_for_collection_relationship` + callable functions. It is important to note that the default relationship + naming derives the name from the **the actual class name**. If you've + given a particular class an explicit name by declaring it, or specified an + alternate class naming scheme, that's the name from which the relationship + name will be derived. + +5. The classes are inspected for an existing mapped property matching these + names. If one is detected on one side, but none on the other side, :class:`.AutomapBase` + attempts to create a relationship on the missing side, then uses the + :paramref:`.relationship.back_populates` parameter in order to point + the new relationship to the other side. + +6. In the usual case where no relationship is on either side, + :meth:`.AutomapBase.prepare` produces a :func:`.relationship` on the "many-to-one" + side and matches it to the other using the :paramref:`.relationship.backref` + parameter. + +7. Production of the :func:`.relationship` and optionally the :func:`.backref` + is handed off to the :paramref:`.AutomapBase.prepare.generate_relationship` + function, which can be supplied by the end-user in order to augment + the arguments passed to :func:`.relationship` or :func:`.backref` or to + make use of custom implementations of these functions. + +Custom Relationship Arguments +----------------------------- + +The :paramref:`.AutomapBase.prepare.generate_relationship` hook can be used +to add parameters to relationships. For most cases, we can make use of the +existing :func:`.automap.generate_relationship` function to return +the object, after augmenting the given keyword dictionary with our own +arguments. + +Below is an illustration of how to send +:paramref:`.relationship.cascade` and +:paramref:`.relationship.passive_deletes` +options along to all one-to-many relationships:: + + from sqlalchemy.ext.automap import generate_relationship + + def _gen_relationship(base, direction, return_fn, + attrname, local_cls, referred_cls, **kw): + if direction is interfaces.ONETOMANY: + kw['cascade'] = 'all, delete-orphan' + kw['passive_deletes'] = True + # make use of the built-in function to actually return + # the result. + return generate_relationship(base, direction, return_fn, + attrname, local_cls, referred_cls, **kw) + + from sqlalchemy.ext.automap import automap_base + from sqlalchemy import create_engine + + # automap base + Base = automap_base() + + engine = create_engine("sqlite:///mydatabase.db") + Base.prepare(engine, reflect=True, + generate_relationship=_gen_relationship) + +Many-to-Many relationships +-------------------------- + +:mod:`.sqlalchemy.ext.automap` will generate many-to-many relationships, e.g. +those which contain a ``secondary`` argument. The process for producing these +is as follows: + +1. A given :class:`.Table` is examined for :class:`.ForeignKeyConstraint` objects, + before any mapped class has been assigned to it. + +2. If the table contains two and exactly two :class:`.ForeignKeyConstraint` + objects, and all columns within this table are members of these two + :class:`.ForeignKeyConstraint` objects, the table is assumed to be a + "secondary" table, and will **not be mapped directly**. + +3. The two (or one, for self-referential) external tables to which the :class:`.Table` + refers to are matched to the classes to which they will be mapped, if any. + +4. If mapped classes for both sides are located, a many-to-many bi-directional + :func:`.relationship` / :func:`.backref` pair is created between the two + classes. + +5. The override logic for many-to-many works the same as that of one-to-many/ + many-to-one; the :func:`.generate_relationship` function is called upon + to generate the strucures and existing attributes will be maintained. + +Using Automap with Explicit Declarations +======================================== + +As noted previously, automap has no dependency on reflection, and can make +use of any collection of :class:`.Table` objects within a :class:`.MetaData` +collection. From this, it follows that automap can also be used +generate missing relationships given an otherwise complete model that fully defines +table metadata:: + + from sqlalchemy.ext.automap import automap_base + from sqlalchemy import Column, Integer, String, ForeignKey + + Base = automap_base() + + class User(Base): + __tablename__ = 'user' + + id = Column(Integer, primary_key=True) + name = Column(String) + + class Address(Base): + __tablename__ = 'address' + + id = Column(Integer, primary_key=True) + email = Column(String) + user_id = Column(ForeignKey('user.id')) + + # produce relationships + Base.prepare() + + # mapping is complete, with "address_collection" and + # "user" relationships + a1 = Address(email='u1') + a2 = Address(email='u2') + u1 = User(address_collection=[a1, a2]) + assert a1.user is u1 + +Above, given mostly complete ``User`` and ``Address`` mappings, the +:class:`.ForeignKey` which we defined on ``Address.user_id`` allowed a +bidirectional relationship pair ``Address.user`` and ``User.address_collection`` +to be generated on the mapped classes. + +Note that when subclassing :class:`.AutomapBase`, the :meth:`.AutomapBase.prepare` +method is required; if not called, the classes we've declared are in an +un-mapped state. + + +""" +from .declarative import declarative_base as _declarative_base +from .declarative.base import _DeferredMapperConfig +from ..sql import and_ +from ..schema import ForeignKeyConstraint +from ..orm import relationship, backref, interfaces +from .. import util + + +def classname_for_table(base, tablename, table): + """Return the class name that should be used, given the name + of a table. + + The default implementation is:: + + return str(tablename) + + Alternate implementations can be specified using the + :paramref:`.AutomapBase.prepare.classname_for_table` + parameter. + + :param base: the :class:`.AutomapBase` class doing the prepare. + + :param tablename: string name of the :class:`.Table`. + + :param table: the :class:`.Table` object itself. + + :return: a string class name. + + .. note:: + + In Python 2, the string used for the class name **must** be a non-Unicode + object, e.g. a ``str()`` object. The ``.name`` attribute of + :class:`.Table` is typically a Python unicode subclass, so the ``str()`` + function should be applied to this name, after accounting for any non-ASCII + characters. + + """ + return str(tablename) + +def name_for_scalar_relationship(base, local_cls, referred_cls, constraint): + """Return the attribute name that should be used to refer from one + class to another, for a scalar object reference. + + The default implementation is:: + + return referred_cls.__name__.lower() + + Alternate implementations can be specified using the + :paramref:`.AutomapBase.prepare.name_for_scalar_relationship` + parameter. + + :param base: the :class:`.AutomapBase` class doing the prepare. + + :param local_cls: the class to be mapped on the local side. + + :param referred_cls: the class to be mapped on the referring side. + + :param constraint: the :class:`.ForeignKeyConstraint` that is being + inspected to produce this relationship. + + """ + return referred_cls.__name__.lower() + +def name_for_collection_relationship(base, local_cls, referred_cls, constraint): + """Return the attribute name that should be used to refer from one + class to another, for a collection reference. + + The default implementation is:: + + return referred_cls.__name__.lower() + "_collection" + + Alternate implementations + can be specified using the :paramref:`.AutomapBase.prepare.name_for_collection_relationship` + parameter. + + :param base: the :class:`.AutomapBase` class doing the prepare. + + :param local_cls: the class to be mapped on the local side. + + :param referred_cls: the class to be mapped on the referring side. + + :param constraint: the :class:`.ForeignKeyConstraint` that is being + inspected to produce this relationship. + + """ + return referred_cls.__name__.lower() + "_collection" + +def generate_relationship(base, direction, return_fn, attrname, local_cls, referred_cls, **kw): + """Generate a :func:`.relationship` or :func:`.backref` on behalf of two + mapped classes. + + An alternate implementation of this function can be specified using the + :paramref:`.AutomapBase.prepare.generate_relationship` parameter. + + The default implementation of this function is as follows:: + + if return_fn is backref: + return return_fn(attrname, **kw) + elif return_fn is relationship: + return return_fn(referred_cls, **kw) + else: + raise TypeError("Unknown relationship function: %s" % return_fn) + + :param base: the :class:`.AutomapBase` class doing the prepare. + + :param direction: indicate the "direction" of the relationship; this will + be one of :data:`.ONETOMANY`, :data:`.MANYTOONE`, :data:`.MANYTOONE`. + + :param return_fn: the function that is used by default to create the + relationship. This will be either :func:`.relationship` or :func:`.backref`. + The :func:`.backref` function's result will be used to produce a new + :func:`.relationship` in a second step, so it is critical that user-defined + implementations correctly differentiate between the two functions, if + a custom relationship function is being used. + + :attrname: the attribute name to which this relationship is being assigned. + If the value of :paramref:`.generate_relationship.return_fn` is the + :func:`.backref` function, then this name is the name that is being + assigned to the backref. + + :param local_cls: the "local" class to which this relationship or backref + will be locally present. + + :param referred_cls: the "referred" class to which the relationship or backref + refers to. + + :param \**kw: all additional keyword arguments are passed along to the + function. + + :return: a :func:`.relationship` or :func:`.backref` construct, as dictated + by the :paramref:`.generate_relationship.return_fn` parameter. + + """ + if return_fn is backref: + return return_fn(attrname, **kw) + elif return_fn is relationship: + return return_fn(referred_cls, **kw) + else: + raise TypeError("Unknown relationship function: %s" % return_fn) + +class AutomapBase(object): + """Base class for an "automap" schema. + + The :class:`.AutomapBase` class can be compared to the "declarative base" + class that is produced by the :func:`.declarative.declarative_base` + function. In practice, the :class:`.AutomapBase` class is always used + as a mixin along with an actual declarative base. + + A new subclassable :class:`.AutomapBase` is typically instantated + using the :func:`.automap_base` function. + + .. seealso:: + + :ref:`automap_toplevel` + + """ + __abstract__ = True + + classes = None + """An instance of :class:`.util.Properties` containing classes. + + This object behaves much like the ``.c`` collection on a table. Classes + are present under the name they were given, e.g.:: + + Base = automap_base() + Base.prepare(engine=some_engine, reflect=True) + + User, Address = Base.classes.User, Base.classes.Address + + """ + + @classmethod + def prepare(cls, + engine=None, + reflect=False, + classname_for_table=classname_for_table, + collection_class=list, + name_for_scalar_relationship=name_for_scalar_relationship, + name_for_collection_relationship=name_for_collection_relationship, + generate_relationship=generate_relationship): + + """Extract mapped classes and relationships from the :class:`.MetaData` and + perform mappings. + + :param engine: an :class:`.Engine` or :class:`.Connection` with which + to perform schema reflection, if specified. + If the :paramref:`.AutomapBase.prepare.reflect` argument is False, this + object is not used. + + :param reflect: if True, the :meth:`.MetaData.reflect` method is called + on the :class:`.MetaData` associated with this :class:`.AutomapBase`. + The :class:`.Engine` passed via :paramref:`.AutomapBase.prepare.engine` will + be used to perform the reflection if present; else, the :class:`.MetaData` + should already be bound to some engine else the operation will fail. + + :param classname_for_table: callable function which will be used to + produce new class names, given a table name. Defaults to + :func:`.classname_for_table`. + + :param name_for_scalar_relationship: callable function which will be used + to produce relationship names for scalar relationships. Defaults to + :func:`.name_for_scalar_relationship`. + + :param name_for_collection_relationship: callable function which will be used + to produce relationship names for collection-oriented relationships. Defaults to + :func:`.name_for_collection_relationship`. + + :param generate_relationship: callable function which will be used to + actually generate :func:`.relationship` and :func:`.backref` constructs. + Defaults to :func:`.generate_relationship`. + + :param collection_class: the Python collection class that will be used + when a new :func:`.relationship` object is created that represents a + collection. Defaults to ``list``. + + """ + if reflect: + cls.metadata.reflect( + engine, + extend_existing=True, + autoload_replace=False + ) + + table_to_map_config = dict( + (m.local_table, m) + for m in _DeferredMapperConfig.classes_for_base(cls) + ) + + many_to_many = [] + + for table in cls.metadata.tables.values(): + lcl_m2m, rem_m2m, m2m_const = _is_many_to_many(cls, table) + if lcl_m2m is not None: + many_to_many.append((lcl_m2m, rem_m2m, m2m_const, table)) + elif not table.primary_key: + continue + elif table not in table_to_map_config: + mapped_cls = type( + classname_for_table(cls, table.name, table), + (cls, ), + {"__table__": table} + ) + map_config = _DeferredMapperConfig.config_for_cls(mapped_cls) + cls.classes[map_config.cls.__name__] = mapped_cls + table_to_map_config[table] = map_config + + for map_config in table_to_map_config.values(): + _relationships_for_fks(cls, + map_config, + table_to_map_config, + collection_class, + name_for_scalar_relationship, + name_for_collection_relationship, + generate_relationship) + + for lcl_m2m, rem_m2m, m2m_const, table in many_to_many: + _m2m_relationship(cls, lcl_m2m, rem_m2m, m2m_const, table, + table_to_map_config, + collection_class, + name_for_scalar_relationship, + name_for_collection_relationship, + generate_relationship) + for map_config in table_to_map_config.values(): + map_config.map() + + + _sa_decl_prepare = True + """Indicate that the mapping of classes should be deferred. + + The presence of this attribute name indicates to declarative + that the call to mapper() should not occur immediately; instead, + information about the table and attributes to be mapped are gathered + into an internal structure called _DeferredMapperConfig. These + objects can be collected later using classes_for_base(), additional + mapping decisions can be made, and then the map() method will actually + apply the mapping. + + The only real reason this deferral of the whole + thing is needed is to support primary key columns that aren't reflected + yet when the class is declared; everything else can theoretically be + added to the mapper later. However, the _DeferredMapperConfig is a + nice interface in any case which exists at that not usually exposed point + at which declarative has the class and the Table but hasn't called + mapper() yet. + + """ + +def automap_base(declarative_base=None, **kw): + """Produce a declarative automap base. + + This function produces a new base class that is a product of the + :class:`.AutomapBase` class as well a declarative base produced by + :func:`.declarative.declarative_base`. + + All parameters other than ``declarative_base`` are keyword arguments + that are passed directly to the :func:`.declarative.declarative_base` + function. + + :param declarative_base: an existing class produced by + :func:`.declarative.declarative_base`. When this is passed, the function + no longer invokes :func:`.declarative.declarative_base` itself, and all other + keyword arguments are ignored. + + :param \**kw: keyword arguments are passed along to + :func:`.declarative.declarative_base`. + + """ + if declarative_base is None: + Base = _declarative_base(**kw) + else: + Base = declarative_base + + return type( + Base.__name__, + (AutomapBase, Base,), + {"__abstract__": True, "classes": util.Properties({})} + ) + +def _is_many_to_many(automap_base, table): + fk_constraints = [const for const in table.constraints + if isinstance(const, ForeignKeyConstraint)] + if len(fk_constraints) != 2: + return None, None, None + + cols = sum( + [[fk.parent for fk in fk_constraint.elements] + for fk_constraint in fk_constraints], []) + + if set(cols) != set(table.c): + return None, None, None + + return ( + fk_constraints[0].elements[0].column.table, + fk_constraints[1].elements[0].column.table, + fk_constraints + ) + +def _relationships_for_fks(automap_base, map_config, table_to_map_config, + collection_class, + name_for_scalar_relationship, + name_for_collection_relationship, + generate_relationship): + local_table = map_config.local_table + local_cls = map_config.cls + + for constraint in local_table.constraints: + if isinstance(constraint, ForeignKeyConstraint): + fks = constraint.elements + referred_table = fks[0].column.table + referred_cfg = table_to_map_config.get(referred_table, None) + if referred_cfg is None: + continue + referred_cls = referred_cfg.cls + + relationship_name = name_for_scalar_relationship( + automap_base, + local_cls, + referred_cls, constraint) + backref_name = name_for_collection_relationship( + automap_base, + referred_cls, + local_cls, + constraint + ) + + create_backref = backref_name not in referred_cfg.properties + + if relationship_name not in map_config.properties: + if create_backref: + backref_obj = generate_relationship(automap_base, + interfaces.ONETOMANY, backref, + backref_name, referred_cls, local_cls, + collection_class=collection_class) + else: + backref_obj = None + map_config.properties[relationship_name] = \ + generate_relationship(automap_base, + interfaces.MANYTOONE, + relationship, + relationship_name, + local_cls, referred_cls, + foreign_keys=[fk.parent for fk in constraint.elements], + backref=backref_obj, + remote_side=[fk.column for fk in constraint.elements] + ) + if not create_backref: + referred_cfg.properties[backref_name].back_populates = relationship_name + elif create_backref: + referred_cfg.properties[backref_name] = \ + generate_relationship(automap_base, + interfaces.ONETOMANY, + relationship, + backref_name, + referred_cls, local_cls, + foreign_keys=[fk.parent for fk in constraint.elements], + back_populates=relationship_name, + collection_class=collection_class) + map_config.properties[relationship_name].back_populates = backref_name + +def _m2m_relationship(automap_base, lcl_m2m, rem_m2m, m2m_const, table, + table_to_map_config, + collection_class, + name_for_scalar_relationship, + name_for_collection_relationship, + generate_relationship): + + map_config = table_to_map_config.get(lcl_m2m, None) + referred_cfg = table_to_map_config.get(rem_m2m, None) + if map_config is None or referred_cfg is None: + return + + local_cls = map_config.cls + referred_cls = referred_cfg.cls + + relationship_name = name_for_collection_relationship( + automap_base, + local_cls, + referred_cls, m2m_const[0]) + backref_name = name_for_collection_relationship( + automap_base, + referred_cls, + local_cls, + m2m_const[1] + ) + + create_backref = backref_name not in referred_cfg.properties + + if relationship_name not in map_config.properties: + if create_backref: + backref_obj = generate_relationship(automap_base, + interfaces.MANYTOMANY, + backref, + backref_name, + referred_cls, local_cls, + collection_class=collection_class + ) + else: + backref_obj = None + map_config.properties[relationship_name] = \ + generate_relationship(automap_base, + interfaces.MANYTOMANY, + relationship, + relationship_name, + local_cls, referred_cls, + secondary=table, + primaryjoin=and_(fk.column == fk.parent for fk in m2m_const[0].elements), + secondaryjoin=and_(fk.column == fk.parent for fk in m2m_const[1].elements), + backref=backref_obj, + collection_class=collection_class + ) + if not create_backref: + referred_cfg.properties[backref_name].back_populates = relationship_name + elif create_backref: + referred_cfg.properties[backref_name] = \ + generate_relationship(automap_base, + interfaces.MANYTOMANY, + relationship, + backref_name, + referred_cls, local_cls, + secondary=table, + primaryjoin=and_(fk.column == fk.parent for fk in m2m_const[1].elements), + secondaryjoin=and_(fk.column == fk.parent for fk in m2m_const[0].elements), + back_populates=relationship_name, + collection_class=collection_class) + map_config.properties[relationship_name].back_populates = backref_name |