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1225 lines
44 KiB
1225 lines
44 KiB
# ext/automap.py
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# Copyright (C) 2005-2022 the SQLAlchemy authors and contributors
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# <see AUTHORS file>
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#
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# This module is part of SQLAlchemy and is released under
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# the MIT License: https://www.opensource.org/licenses/mit-license.php
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r"""Define an extension to the :mod:`sqlalchemy.ext.declarative` system
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which automatically generates mapped classes and relationships from a database
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schema, typically though not necessarily one which is reflected.
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.. versionadded:: 0.9.1 Added :mod:`sqlalchemy.ext.automap`.
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It is hoped that the :class:`.AutomapBase` system provides a quick
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and modernized solution to the problem that the very famous
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`SQLSoup <https://sqlsoup.readthedocs.io/en/latest/>`_
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also tries to solve, that of generating a quick and rudimentary object
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model from an existing database on the fly. By addressing the issue strictly
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at the mapper configuration level, and integrating fully with existing
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Declarative class techniques, :class:`.AutomapBase` seeks to provide
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a well-integrated approach to the issue of expediently auto-generating ad-hoc
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mappings.
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Basic Use
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=========
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The simplest usage is to reflect an existing database into a new model.
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We create a new :class:`.AutomapBase` class in a similar manner as to how
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we create a declarative base class, using :func:`.automap_base`.
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We then call :meth:`.AutomapBase.prepare` on the resulting base class,
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asking it to reflect the schema and produce mappings::
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from sqlalchemy.ext.automap import automap_base
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from sqlalchemy.orm import Session
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from sqlalchemy import create_engine
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Base = automap_base()
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# engine, suppose it has two tables 'user' and 'address' set up
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engine = create_engine("sqlite:///mydatabase.db")
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# reflect the tables
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Base.prepare(engine, reflect=True)
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# mapped classes are now created with names by default
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# matching that of the table name.
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User = Base.classes.user
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Address = Base.classes.address
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session = Session(engine)
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# rudimentary relationships are produced
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session.add(Address(email_address="foo@bar.com", user=User(name="foo")))
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session.commit()
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# collection-based relationships are by default named
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# "<classname>_collection"
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print (u1.address_collection)
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Above, calling :meth:`.AutomapBase.prepare` while passing along the
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:paramref:`.AutomapBase.prepare.reflect` parameter indicates that the
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:meth:`_schema.MetaData.reflect`
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method will be called on this declarative base
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classes' :class:`_schema.MetaData` collection; then, each **viable**
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:class:`_schema.Table` within the :class:`_schema.MetaData`
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will get a new mapped class
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generated automatically. The :class:`_schema.ForeignKeyConstraint`
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objects which
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link the various tables together will be used to produce new, bidirectional
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:func:`_orm.relationship` objects between classes.
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The classes and relationships
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follow along a default naming scheme that we can customize. At this point,
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our basic mapping consisting of related ``User`` and ``Address`` classes is
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ready to use in the traditional way.
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.. note:: By **viable**, we mean that for a table to be mapped, it must
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specify a primary key. Additionally, if the table is detected as being
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a pure association table between two other tables, it will not be directly
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mapped and will instead be configured as a many-to-many table between
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the mappings for the two referring tables.
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Generating Mappings from an Existing MetaData
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=============================================
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We can pass a pre-declared :class:`_schema.MetaData` object to
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:func:`.automap_base`.
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This object can be constructed in any way, including programmatically, from
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a serialized file, or from itself being reflected using
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:meth:`_schema.MetaData.reflect`.
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Below we illustrate a combination of reflection and
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explicit table declaration::
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from sqlalchemy import create_engine, MetaData, Table, Column, ForeignKey
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from sqlalchemy.ext.automap import automap_base
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engine = create_engine("sqlite:///mydatabase.db")
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# produce our own MetaData object
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metadata = MetaData()
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# we can reflect it ourselves from a database, using options
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# such as 'only' to limit what tables we look at...
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metadata.reflect(engine, only=['user', 'address'])
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# ... or just define our own Table objects with it (or combine both)
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Table('user_order', metadata,
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Column('id', Integer, primary_key=True),
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Column('user_id', ForeignKey('user.id'))
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)
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# we can then produce a set of mappings from this MetaData.
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Base = automap_base(metadata=metadata)
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# calling prepare() just sets up mapped classes and relationships.
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Base.prepare()
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# mapped classes are ready
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User, Address, Order = Base.classes.user, Base.classes.address,\
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Base.classes.user_order
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Specifying Classes Explicitly
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=============================
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The :mod:`.sqlalchemy.ext.automap` extension allows classes to be defined
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explicitly, in a way similar to that of the :class:`.DeferredReflection` class.
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Classes that extend from :class:`.AutomapBase` act like regular declarative
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classes, but are not immediately mapped after their construction, and are
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instead mapped when we call :meth:`.AutomapBase.prepare`. The
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:meth:`.AutomapBase.prepare` method will make use of the classes we've
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established based on the table name we use. If our schema contains tables
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``user`` and ``address``, we can define one or both of the classes to be used::
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from sqlalchemy.ext.automap import automap_base
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from sqlalchemy import create_engine
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# automap base
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Base = automap_base()
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# pre-declare User for the 'user' table
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class User(Base):
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__tablename__ = 'user'
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# override schema elements like Columns
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user_name = Column('name', String)
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# override relationships too, if desired.
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# we must use the same name that automap would use for the
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# relationship, and also must refer to the class name that automap will
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# generate for "address"
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address_collection = relationship("address", collection_class=set)
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# reflect
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engine = create_engine("sqlite:///mydatabase.db")
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Base.prepare(engine, reflect=True)
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# we still have Address generated from the tablename "address",
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# but User is the same as Base.classes.User now
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Address = Base.classes.address
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u1 = session.query(User).first()
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print (u1.address_collection)
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# the backref is still there:
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a1 = session.query(Address).first()
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print (a1.user)
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Above, one of the more intricate details is that we illustrated overriding
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one of the :func:`_orm.relationship` objects that automap would have created.
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To do this, we needed to make sure the names match up with what automap
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would normally generate, in that the relationship name would be
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``User.address_collection`` and the name of the class referred to, from
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automap's perspective, is called ``address``, even though we are referring to
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it as ``Address`` within our usage of this class.
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Overriding Naming Schemes
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=========================
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:mod:`.sqlalchemy.ext.automap` is tasked with producing mapped classes and
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relationship names based on a schema, which means it has decision points in how
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these names are determined. These three decision points are provided using
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functions which can be passed to the :meth:`.AutomapBase.prepare` method, and
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are known as :func:`.classname_for_table`,
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:func:`.name_for_scalar_relationship`,
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and :func:`.name_for_collection_relationship`. Any or all of these
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functions are provided as in the example below, where we use a "camel case"
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scheme for class names and a "pluralizer" for collection names using the
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`Inflect <https://pypi.org/project/inflect>`_ package::
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import re
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import inflect
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def camelize_classname(base, tablename, table):
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"Produce a 'camelized' class name, e.g. "
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"'words_and_underscores' -> 'WordsAndUnderscores'"
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return str(tablename[0].upper() + \
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re.sub(r'_([a-z])', lambda m: m.group(1).upper(), tablename[1:]))
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_pluralizer = inflect.engine()
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def pluralize_collection(base, local_cls, referred_cls, constraint):
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"Produce an 'uncamelized', 'pluralized' class name, e.g. "
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"'SomeTerm' -> 'some_terms'"
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referred_name = referred_cls.__name__
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uncamelized = re.sub(r'[A-Z]',
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lambda m: "_%s" % m.group(0).lower(),
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referred_name)[1:]
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pluralized = _pluralizer.plural(uncamelized)
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return pluralized
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from sqlalchemy.ext.automap import automap_base
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Base = automap_base()
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engine = create_engine("sqlite:///mydatabase.db")
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Base.prepare(engine, reflect=True,
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classname_for_table=camelize_classname,
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name_for_collection_relationship=pluralize_collection
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)
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From the above mapping, we would now have classes ``User`` and ``Address``,
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where the collection from ``User`` to ``Address`` is called
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``User.addresses``::
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User, Address = Base.classes.User, Base.classes.Address
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u1 = User(addresses=[Address(email="foo@bar.com")])
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Relationship Detection
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======================
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The vast majority of what automap accomplishes is the generation of
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:func:`_orm.relationship` structures based on foreign keys. The mechanism
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by which this works for many-to-one and one-to-many relationships is as
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follows:
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1. A given :class:`_schema.Table`, known to be mapped to a particular class,
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is examined for :class:`_schema.ForeignKeyConstraint` objects.
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2. From each :class:`_schema.ForeignKeyConstraint`, the remote
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:class:`_schema.Table`
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object present is matched up to the class to which it is to be mapped,
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if any, else it is skipped.
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3. As the :class:`_schema.ForeignKeyConstraint`
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we are examining corresponds to a
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reference from the immediate mapped class, the relationship will be set up
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as a many-to-one referring to the referred class; a corresponding
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one-to-many backref will be created on the referred class referring
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to this class.
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4. If any of the columns that are part of the
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:class:`_schema.ForeignKeyConstraint`
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are not nullable (e.g. ``nullable=False``), a
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:paramref:`_orm.relationship.cascade` keyword argument
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of ``all, delete-orphan`` will be added to the keyword arguments to
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be passed to the relationship or backref. If the
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:class:`_schema.ForeignKeyConstraint` reports that
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:paramref:`_schema.ForeignKeyConstraint.ondelete`
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is set to ``CASCADE`` for a not null or ``SET NULL`` for a nullable
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set of columns, the option :paramref:`_orm.relationship.passive_deletes`
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flag is set to ``True`` in the set of relationship keyword arguments.
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Note that not all backends support reflection of ON DELETE.
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.. versionadded:: 1.0.0 - automap will detect non-nullable foreign key
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constraints when producing a one-to-many relationship and establish
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a default cascade of ``all, delete-orphan`` if so; additionally,
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if the constraint specifies
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:paramref:`_schema.ForeignKeyConstraint.ondelete`
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of ``CASCADE`` for non-nullable or ``SET NULL`` for nullable columns,
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the ``passive_deletes=True`` option is also added.
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5. The names of the relationships are determined using the
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:paramref:`.AutomapBase.prepare.name_for_scalar_relationship` and
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:paramref:`.AutomapBase.prepare.name_for_collection_relationship`
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callable functions. It is important to note that the default relationship
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naming derives the name from the **the actual class name**. If you've
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given a particular class an explicit name by declaring it, or specified an
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alternate class naming scheme, that's the name from which the relationship
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name will be derived.
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6. The classes are inspected for an existing mapped property matching these
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names. If one is detected on one side, but none on the other side,
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:class:`.AutomapBase` attempts to create a relationship on the missing side,
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then uses the :paramref:`_orm.relationship.back_populates`
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parameter in order to
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point the new relationship to the other side.
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7. In the usual case where no relationship is on either side,
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:meth:`.AutomapBase.prepare` produces a :func:`_orm.relationship` on the
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"many-to-one" side and matches it to the other using the
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:paramref:`_orm.relationship.backref` parameter.
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8. Production of the :func:`_orm.relationship` and optionally the
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:func:`.backref`
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is handed off to the :paramref:`.AutomapBase.prepare.generate_relationship`
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function, which can be supplied by the end-user in order to augment
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the arguments passed to :func:`_orm.relationship` or :func:`.backref` or to
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make use of custom implementations of these functions.
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Custom Relationship Arguments
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-----------------------------
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The :paramref:`.AutomapBase.prepare.generate_relationship` hook can be used
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to add parameters to relationships. For most cases, we can make use of the
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existing :func:`.automap.generate_relationship` function to return
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the object, after augmenting the given keyword dictionary with our own
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arguments.
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Below is an illustration of how to send
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:paramref:`_orm.relationship.cascade` and
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:paramref:`_orm.relationship.passive_deletes`
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options along to all one-to-many relationships::
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from sqlalchemy.ext.automap import generate_relationship
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def _gen_relationship(base, direction, return_fn,
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attrname, local_cls, referred_cls, **kw):
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if direction is interfaces.ONETOMANY:
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kw['cascade'] = 'all, delete-orphan'
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kw['passive_deletes'] = True
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# make use of the built-in function to actually return
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# the result.
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return generate_relationship(base, direction, return_fn,
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attrname, local_cls, referred_cls, **kw)
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from sqlalchemy.ext.automap import automap_base
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from sqlalchemy import create_engine
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# automap base
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Base = automap_base()
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engine = create_engine("sqlite:///mydatabase.db")
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Base.prepare(engine, reflect=True,
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generate_relationship=_gen_relationship)
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Many-to-Many relationships
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--------------------------
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:mod:`.sqlalchemy.ext.automap` will generate many-to-many relationships, e.g.
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those which contain a ``secondary`` argument. The process for producing these
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is as follows:
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1. A given :class:`_schema.Table` is examined for
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:class:`_schema.ForeignKeyConstraint`
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objects, before any mapped class has been assigned to it.
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2. If the table contains two and exactly two
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:class:`_schema.ForeignKeyConstraint`
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objects, and all columns within this table are members of these two
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:class:`_schema.ForeignKeyConstraint` objects, the table is assumed to be a
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"secondary" table, and will **not be mapped directly**.
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3. The two (or one, for self-referential) external tables to which the
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:class:`_schema.Table`
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refers to are matched to the classes to which they will be
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mapped, if any.
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4. If mapped classes for both sides are located, a many-to-many bi-directional
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:func:`_orm.relationship` / :func:`.backref`
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pair is created between the two
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classes.
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5. The override logic for many-to-many works the same as that of one-to-many/
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many-to-one; the :func:`.generate_relationship` function is called upon
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to generate the structures and existing attributes will be maintained.
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Relationships with Inheritance
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------------------------------
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:mod:`.sqlalchemy.ext.automap` will not generate any relationships between
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two classes that are in an inheritance relationship. That is, with two
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classes given as follows::
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class Employee(Base):
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__tablename__ = 'employee'
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id = Column(Integer, primary_key=True)
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type = Column(String(50))
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__mapper_args__ = {
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'polymorphic_identity':'employee', 'polymorphic_on': type
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}
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class Engineer(Employee):
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__tablename__ = 'engineer'
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id = Column(Integer, ForeignKey('employee.id'), primary_key=True)
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__mapper_args__ = {
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'polymorphic_identity':'engineer',
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}
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The foreign key from ``Engineer`` to ``Employee`` is used not for a
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relationship, but to establish joined inheritance between the two classes.
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Note that this means automap will not generate *any* relationships
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for foreign keys that link from a subclass to a superclass. If a mapping
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has actual relationships from subclass to superclass as well, those
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need to be explicit. Below, as we have two separate foreign keys
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from ``Engineer`` to ``Employee``, we need to set up both the relationship
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we want as well as the ``inherit_condition``, as these are not things
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SQLAlchemy can guess::
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class Employee(Base):
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__tablename__ = 'employee'
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id = Column(Integer, primary_key=True)
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type = Column(String(50))
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__mapper_args__ = {
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'polymorphic_identity':'employee', 'polymorphic_on':type
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}
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class Engineer(Employee):
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__tablename__ = 'engineer'
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id = Column(Integer, ForeignKey('employee.id'), primary_key=True)
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favorite_employee_id = Column(Integer, ForeignKey('employee.id'))
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favorite_employee = relationship(Employee,
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foreign_keys=favorite_employee_id)
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__mapper_args__ = {
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'polymorphic_identity':'engineer',
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'inherit_condition': id == Employee.id
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}
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Handling Simple Naming Conflicts
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--------------------------------
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In the case of naming conflicts during mapping, override any of
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:func:`.classname_for_table`, :func:`.name_for_scalar_relationship`,
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and :func:`.name_for_collection_relationship` as needed. For example, if
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automap is attempting to name a many-to-one relationship the same as an
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existing column, an alternate convention can be conditionally selected. Given
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a schema:
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.. sourcecode:: sql
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CREATE TABLE table_a (
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id INTEGER PRIMARY KEY
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);
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CREATE TABLE table_b (
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id INTEGER PRIMARY KEY,
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table_a INTEGER,
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FOREIGN KEY(table_a) REFERENCES table_a(id)
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);
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The above schema will first automap the ``table_a`` table as a class named
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``table_a``; it will then automap a relationship onto the class for ``table_b``
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with the same name as this related class, e.g. ``table_a``. This
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relationship name conflicts with the mapping column ``table_b.table_a``,
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and will emit an error on mapping.
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We can resolve this conflict by using an underscore as follows::
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def name_for_scalar_relationship(base, local_cls, referred_cls, constraint):
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name = referred_cls.__name__.lower()
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local_table = local_cls.__table__
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if name in local_table.columns:
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newname = name + "_"
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warnings.warn(
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"Already detected name %s present. using %s" %
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(name, newname))
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return newname
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return name
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Base.prepare(engine, reflect=True,
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name_for_scalar_relationship=name_for_scalar_relationship)
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Alternatively, we can change the name on the column side. The columns
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that are mapped can be modified using the technique described at
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:ref:`mapper_column_distinct_names`, by assigning the column explicitly
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to a new name::
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Base = automap_base()
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class TableB(Base):
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__tablename__ = 'table_b'
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_table_a = Column('table_a', ForeignKey('table_a.id'))
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Base.prepare(engine, reflect=True)
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Using Automap with Explicit Declarations
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========================================
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As noted previously, automap has no dependency on reflection, and can make
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use of any collection of :class:`_schema.Table` objects within a
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:class:`_schema.MetaData`
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collection. From this, it follows that automap can also be used
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generate missing relationships given an otherwise complete model that fully
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defines table metadata::
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from sqlalchemy.ext.automap import automap_base
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from sqlalchemy import Column, Integer, String, ForeignKey
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Base = automap_base()
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class User(Base):
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__tablename__ = 'user'
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id = Column(Integer, primary_key=True)
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name = Column(String)
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class Address(Base):
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__tablename__ = 'address'
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id = Column(Integer, primary_key=True)
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email = Column(String)
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user_id = Column(ForeignKey('user.id'))
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# produce relationships
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Base.prepare()
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# mapping is complete, with "address_collection" and
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# "user" relationships
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a1 = Address(email='u1')
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a2 = Address(email='u2')
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u1 = User(address_collection=[a1, a2])
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assert a1.user is u1
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Above, given mostly complete ``User`` and ``Address`` mappings, the
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:class:`_schema.ForeignKey` which we defined on ``Address.user_id`` allowed a
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bidirectional relationship pair ``Address.user`` and
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``User.address_collection`` to be generated on the mapped classes.
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Note that when subclassing :class:`.AutomapBase`,
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the :meth:`.AutomapBase.prepare` method is required; if not called, the classes
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we've declared are in an un-mapped state.
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.. _automap_intercepting_columns:
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Intercepting Column Definitions
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===============================
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The :class:`_schema.MetaData` and :class:`_schema.Table` objects support an
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event hook :meth:`_events.DDLEvents.column_reflect` that may be used to intercept
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the information reflected about a database column before the :class:`_schema.Column`
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object is constructed. For example if we wanted to map columns using a
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naming convention such as ``"attr_<columnname>"``, the event could
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be applied as::
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@event.listens_for(Base.metadata, "column_reflect")
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def column_reflect(inspector, table, column_info):
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# set column.key = "attr_<lower_case_name>"
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column_info['key'] = "attr_%s" % column_info['name'].lower()
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# run reflection
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Base.prepare(engine, reflect=True)
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.. versionadded:: 1.4.0b2 the :meth:`_events.DDLEvents.column_reflect` event
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may be applied to a :class:`_schema.MetaData` object.
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.. seealso::
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:meth:`_events.DDLEvents.column_reflect`
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:ref:`mapper_automated_reflection_schemes` - in the ORM mapping documentation
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""" # noqa
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from .. import util
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from ..orm import backref
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from ..orm import declarative_base as _declarative_base
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from ..orm import exc as orm_exc
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from ..orm import interfaces
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from ..orm import relationship
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from ..orm.decl_base import _DeferredMapperConfig
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from ..orm.mapper import _CONFIGURE_MUTEX
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from ..schema import ForeignKeyConstraint
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from ..sql import and_
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def classname_for_table(base, tablename, table):
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"""Return the class name that should be used, given the name
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of a table.
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The default implementation is::
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return str(tablename)
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Alternate implementations can be specified using the
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:paramref:`.AutomapBase.prepare.classname_for_table`
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parameter.
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:param base: the :class:`.AutomapBase` class doing the prepare.
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:param tablename: string name of the :class:`_schema.Table`.
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:param table: the :class:`_schema.Table` object itself.
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:return: a string class name.
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.. note::
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In Python 2, the string used for the class name **must** be a
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non-Unicode object, e.g. a ``str()`` object. The ``.name`` attribute
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of :class:`_schema.Table` is typically a Python unicode subclass,
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so the
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``str()`` function should be applied to this name, after accounting for
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any non-ASCII characters.
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"""
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return str(tablename)
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def name_for_scalar_relationship(base, local_cls, referred_cls, constraint):
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"""Return the attribute name that should be used to refer from one
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class to another, for a scalar object reference.
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The default implementation is::
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return referred_cls.__name__.lower()
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Alternate implementations can be specified using the
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:paramref:`.AutomapBase.prepare.name_for_scalar_relationship`
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parameter.
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:param base: the :class:`.AutomapBase` class doing the prepare.
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:param local_cls: the class to be mapped on the local side.
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:param referred_cls: the class to be mapped on the referring side.
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:param constraint: the :class:`_schema.ForeignKeyConstraint` that is being
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inspected to produce this relationship.
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"""
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return referred_cls.__name__.lower()
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def name_for_collection_relationship(
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base, local_cls, referred_cls, constraint
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):
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"""Return the attribute name that should be used to refer from one
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class to another, for a collection reference.
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The default implementation is::
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return referred_cls.__name__.lower() + "_collection"
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Alternate implementations
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can be specified using the
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:paramref:`.AutomapBase.prepare.name_for_collection_relationship`
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parameter.
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:param base: the :class:`.AutomapBase` class doing the prepare.
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:param local_cls: the class to be mapped on the local side.
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:param referred_cls: the class to be mapped on the referring side.
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:param constraint: the :class:`_schema.ForeignKeyConstraint` that is being
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inspected to produce this relationship.
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"""
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return referred_cls.__name__.lower() + "_collection"
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def generate_relationship(
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base, direction, return_fn, attrname, local_cls, referred_cls, **kw
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):
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r"""Generate a :func:`_orm.relationship` or :func:`.backref`
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on behalf of two
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mapped classes.
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An alternate implementation of this function can be specified using the
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:paramref:`.AutomapBase.prepare.generate_relationship` parameter.
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The default implementation of this function is as follows::
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if return_fn is backref:
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return return_fn(attrname, **kw)
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elif return_fn is relationship:
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return return_fn(referred_cls, **kw)
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else:
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raise TypeError("Unknown relationship function: %s" % return_fn)
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:param base: the :class:`.AutomapBase` class doing the prepare.
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:param direction: indicate the "direction" of the relationship; this will
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be one of :data:`.ONETOMANY`, :data:`.MANYTOONE`, :data:`.MANYTOMANY`.
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:param return_fn: the function that is used by default to create the
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relationship. This will be either :func:`_orm.relationship` or
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:func:`.backref`. The :func:`.backref` function's result will be used to
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produce a new :func:`_orm.relationship` in a second step,
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so it is critical
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that user-defined implementations correctly differentiate between the two
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functions, if a custom relationship function is being used.
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:param attrname: the attribute name to which this relationship is being
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assigned. If the value of :paramref:`.generate_relationship.return_fn` is
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the :func:`.backref` function, then this name is the name that is being
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assigned to the backref.
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:param local_cls: the "local" class to which this relationship or backref
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will be locally present.
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:param referred_cls: the "referred" class to which the relationship or
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backref refers to.
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:param \**kw: all additional keyword arguments are passed along to the
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function.
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:return: a :func:`_orm.relationship` or :func:`.backref` construct,
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as dictated
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by the :paramref:`.generate_relationship.return_fn` parameter.
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"""
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if return_fn is backref:
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return return_fn(attrname, **kw)
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elif return_fn is relationship:
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return return_fn(referred_cls, **kw)
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else:
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raise TypeError("Unknown relationship function: %s" % return_fn)
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class AutomapBase(object):
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"""Base class for an "automap" schema.
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The :class:`.AutomapBase` class can be compared to the "declarative base"
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class that is produced by the :func:`.declarative.declarative_base`
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function. In practice, the :class:`.AutomapBase` class is always used
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as a mixin along with an actual declarative base.
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A new subclassable :class:`.AutomapBase` is typically instantiated
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using the :func:`.automap_base` function.
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.. seealso::
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:ref:`automap_toplevel`
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"""
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__abstract__ = True
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classes = None
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"""An instance of :class:`.util.Properties` containing classes.
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This object behaves much like the ``.c`` collection on a table. Classes
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are present under the name they were given, e.g.::
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Base = automap_base()
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Base.prepare(engine=some_engine, reflect=True)
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User, Address = Base.classes.User, Base.classes.Address
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"""
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@classmethod
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@util.deprecated_params(
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engine=(
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"2.0",
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|
"The :paramref:`_automap.AutomapBase.prepare.engine` parameter "
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|
"is deprecated and will be removed in a future release. "
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"Please use the "
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|
":paramref:`_automap.AutomapBase.prepare.autoload_with` "
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"parameter.",
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),
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reflect=(
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"2.0",
|
|
"The :paramref:`_automap.AutomapBase.prepare.reflect` "
|
|
"parameter is deprecated and will be removed in a future "
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"release. Reflection is enabled when "
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|
":paramref:`_automap.AutomapBase.prepare.autoload_with` "
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|
"is passed.",
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),
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)
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def prepare(
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cls,
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autoload_with=None,
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engine=None,
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reflect=False,
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schema=None,
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classname_for_table=None,
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collection_class=None,
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name_for_scalar_relationship=None,
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name_for_collection_relationship=None,
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generate_relationship=None,
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reflection_options=util.EMPTY_DICT,
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):
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"""Extract mapped classes and relationships from the
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:class:`_schema.MetaData` and
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perform mappings.
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|
:param engine: an :class:`_engine.Engine` or
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:class:`_engine.Connection` with which
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to perform schema reflection, if specified.
|
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If the :paramref:`.AutomapBase.prepare.reflect` argument is False,
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this object is not used.
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:param reflect: if True, the :meth:`_schema.MetaData.reflect`
|
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method is called
|
|
on the :class:`_schema.MetaData` associated with this
|
|
:class:`.AutomapBase`.
|
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The :class:`_engine.Engine` passed via
|
|
:paramref:`.AutomapBase.prepare.engine` will be used to perform the
|
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reflection if present; else, the :class:`_schema.MetaData`
|
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should already be
|
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bound to some engine else the operation will fail.
|
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|
|
: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`.
|
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|
|
: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:`_orm.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:`_orm.relationship`
|
|
object is created that represents a
|
|
collection. Defaults to ``list``.
|
|
|
|
:param schema: When present in conjunction with the
|
|
:paramref:`.AutomapBase.prepare.reflect` flag, is passed to
|
|
:meth:`_schema.MetaData.reflect`
|
|
to indicate the primary schema where tables
|
|
should be reflected from. When omitted, the default schema in use
|
|
by the database connection is used.
|
|
|
|
.. versionadded:: 1.1
|
|
|
|
:param reflection_options: When present, this dictionary of options
|
|
will be passed to :meth:`_schema.MetaData.reflect`
|
|
to supply general reflection-specific options like ``only`` and/or
|
|
dialect-specific options like ``oracle_resolve_synonyms``.
|
|
|
|
.. versionadded:: 1.4
|
|
|
|
"""
|
|
glbls = globals()
|
|
if classname_for_table is None:
|
|
classname_for_table = glbls["classname_for_table"]
|
|
if name_for_scalar_relationship is None:
|
|
name_for_scalar_relationship = glbls[
|
|
"name_for_scalar_relationship"
|
|
]
|
|
if name_for_collection_relationship is None:
|
|
name_for_collection_relationship = glbls[
|
|
"name_for_collection_relationship"
|
|
]
|
|
if generate_relationship is None:
|
|
generate_relationship = glbls["generate_relationship"]
|
|
if collection_class is None:
|
|
collection_class = list
|
|
|
|
if autoload_with:
|
|
reflect = True
|
|
|
|
if engine:
|
|
autoload_with = engine
|
|
|
|
if reflect:
|
|
opts = dict(
|
|
schema=schema,
|
|
extend_existing=True,
|
|
autoload_replace=False,
|
|
)
|
|
if reflection_options:
|
|
opts.update(reflection_options)
|
|
cls.metadata.reflect(autoload_with, **opts)
|
|
|
|
with _CONFIGURE_MUTEX:
|
|
table_to_map_config = dict(
|
|
(m.local_table, m)
|
|
for m in _DeferredMapperConfig.classes_for_base(
|
|
cls, sort=False
|
|
)
|
|
)
|
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|
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 _DeferredMapperConfig.classes_for_base(cls):
|
|
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.
|
|
|
|
"""
|
|
|
|
@classmethod
|
|
def _sa_raise_deferred_config(cls):
|
|
raise orm_exc.UnmappedClassError(
|
|
cls,
|
|
msg="Class %s is a subclass of AutomapBase. "
|
|
"Mappings are not produced until the .prepare() "
|
|
"method is called on the class hierarchy."
|
|
% orm_exc._safe_cls_name(cls),
|
|
)
|
|
|
|
|
|
def automap_base(declarative_base=None, **kw):
|
|
r"""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 # derived from a weakref, may be None
|
|
|
|
if local_table is None or local_cls is None:
|
|
return
|
|
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
|
|
|
|
if local_cls is not referred_cls and issubclass(
|
|
local_cls, referred_cls
|
|
):
|
|
continue
|
|
|
|
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
|
|
)
|
|
|
|
o2m_kws = {}
|
|
nullable = False not in {fk.parent.nullable for fk in fks}
|
|
if not nullable:
|
|
o2m_kws["cascade"] = "all, delete-orphan"
|
|
|
|
if (
|
|
constraint.ondelete
|
|
and constraint.ondelete.lower() == "cascade"
|
|
):
|
|
o2m_kws["passive_deletes"] = True
|
|
else:
|
|
if (
|
|
constraint.ondelete
|
|
and constraint.ondelete.lower() == "set null"
|
|
):
|
|
o2m_kws["passive_deletes"] = True
|
|
|
|
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,
|
|
**o2m_kws
|
|
)
|
|
else:
|
|
backref_obj = None
|
|
rel = 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 rel is not None:
|
|
map_config.properties[relationship_name] = rel
|
|
if not create_backref:
|
|
referred_cfg.properties[
|
|
backref_name
|
|
].back_populates = relationship_name
|
|
elif create_backref:
|
|
rel = 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,
|
|
**o2m_kws
|
|
)
|
|
if rel is not None:
|
|
referred_cfg.properties[backref_name] = rel
|
|
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 table in table_to_map_config:
|
|
overlaps = "__*"
|
|
else:
|
|
overlaps = None
|
|
|
|
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,
|
|
overlaps=overlaps,
|
|
)
|
|
else:
|
|
backref_obj = None
|
|
|
|
rel = generate_relationship(
|
|
automap_base,
|
|
interfaces.MANYTOMANY,
|
|
relationship,
|
|
relationship_name,
|
|
local_cls,
|
|
referred_cls,
|
|
overlaps=overlaps,
|
|
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 rel is not None:
|
|
map_config.properties[relationship_name] = rel
|
|
|
|
if not create_backref:
|
|
referred_cfg.properties[
|
|
backref_name
|
|
].back_populates = relationship_name
|
|
elif create_backref:
|
|
rel = generate_relationship(
|
|
automap_base,
|
|
interfaces.MANYTOMANY,
|
|
relationship,
|
|
backref_name,
|
|
referred_cls,
|
|
local_cls,
|
|
overlaps=overlaps,
|
|
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,
|
|
)
|
|
if rel is not None:
|
|
referred_cfg.properties[backref_name] = rel
|
|
map_config.properties[
|
|
relationship_name
|
|
].back_populates = backref_name
|