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Module « sqlalchemy.orm »

Fonction declarative_base - module sqlalchemy.orm

Signature de la fonction declarative_base

def declarative_base(*, metadata: 'Optional[MetaData]' = None, mapper: 'Optional[Callable[..., Mapper[Any]]]' = None, cls: 'Type[Any]' = <class 'object'>, name: 'str' = 'Base', class_registry: 'Optional[clsregistry._ClsRegistryType]' = None, type_annotation_map: 'Optional[_TypeAnnotationMapType]' = None, constructor: 'Callable[..., None]' = <function _declarative_constructor at 0x0000020DA13BC2C0>, metaclass: 'Type[Any]' = <class 'sqlalchemy.orm.decl_api.DeclarativeMeta'>) -> 'Any' 

Description

help(sqlalchemy.orm.declarative_base)

Construct a base class for declarative class definitions.

The new base class will be given a metaclass that produces
appropriate :class:`~sqlalchemy.schema.Table` objects and makes
the appropriate :class:`_orm.Mapper` calls based on the
information provided declaratively in the class and any subclasses
of the class.

.. versionchanged:: 2.0 Note that the :func:`_orm.declarative_base`
   function is superseded by the new :class:`_orm.DeclarativeBase` class,
   which generates a new "base" class using subclassing, rather than
   return value of a function.  This allows an approach that is compatible
   with :pep:`484` typing tools.

The :func:`_orm.declarative_base` function is a shorthand version
of using the :meth:`_orm.registry.generate_base`
method.  That is, the following::

    from sqlalchemy.orm import declarative_base

    Base = declarative_base()

Is equivalent to::

    from sqlalchemy.orm import registry

    mapper_registry = registry()
    Base = mapper_registry.generate_base()

See the docstring for :class:`_orm.registry`
and :meth:`_orm.registry.generate_base`
for more details.

.. versionchanged:: 1.4  The :func:`_orm.declarative_base`
   function is now a specialization of the more generic
   :class:`_orm.registry` class.  The function also moves to the
   ``sqlalchemy.orm`` package from the ``declarative.ext`` package.


:param metadata:
  An optional :class:`~sqlalchemy.schema.MetaData` instance.  All
  :class:`~sqlalchemy.schema.Table` objects implicitly declared by
  subclasses of the base will share this MetaData.  A MetaData instance
  will be created if none is provided.  The
  :class:`~sqlalchemy.schema.MetaData` instance will be available via the
  ``metadata`` attribute of the generated declarative base class.

:param mapper:
  An optional callable, defaults to :class:`_orm.Mapper`. Will
  be used to map subclasses to their Tables.

:param cls:
  Defaults to :class:`object`. A type to use as the base for the generated
  declarative base class. May be a class or tuple of classes.

:param name:
  Defaults to ``Base``.  The display name for the generated
  class.  Customizing this is not required, but can improve clarity in
  tracebacks and debugging.

:param constructor:
  Specify the implementation for the ``__init__`` function on a mapped
  class that has no ``__init__`` of its own.  Defaults to an
  implementation that assigns \**kwargs for declared
  fields and relationships to an instance.  If ``None`` is supplied,
  no __init__ will be provided and construction will fall back to
  cls.__init__ by way of the normal Python semantics.

:param class_registry: optional dictionary that will serve as the
  registry of class names-> mapped classes when string names
  are used to identify classes inside of :func:`_orm.relationship`
  and others.  Allows two or more declarative base classes
  to share the same registry of class names for simplified
  inter-base relationships.

:param type_annotation_map: optional dictionary of Python types to
    SQLAlchemy :class:`_types.TypeEngine` classes or instances.  This
    is used exclusively by the :class:`_orm.MappedColumn` construct
    to produce column types based on annotations within the
    :class:`_orm.Mapped` type.


    .. versionadded:: 2.0

    .. seealso::

        :ref:`orm_declarative_mapped_column_type_map`

:param metaclass:
  Defaults to :class:`.DeclarativeMeta`.  A metaclass or __metaclass__
  compatible callable to use as the meta type of the generated
  declarative base class.

.. seealso::

    :class:`_orm.registry`

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