Class registry

lib/sqlalchemy/orm/decl_api.py:1117–1883

Generalized registry for mapping classes. The :class:`_orm.registry` serves as the basis for maintaining a collection of mappings, and provides configurational hooks used to map classes. The three general kinds of mappings supported are Declarative Base, Declarative Decorator, and

class registry:
    """Generalized registry for mapping classes.

    The :class:`_orm.registry` serves as the basis for maintaining a collection
    of mappings, and provides configurational hooks used to map classes.

    The three general kinds of mappings supported are Declarative Base,
    Declarative Decorator, and Imperative Mapping.   All of these mapping
    styles may be used interchangeably:

    * :meth:`_orm.registry.generate_base` returns a new declarative base
      class, and is the underlying implementation of the
      :func:`_orm.declarative_base` function.

    * :meth:`_orm.registry.mapped` provides a class decorator that will
      apply declarative mapping to a class without the use of a declarative
      base class.

    * :meth:`_orm.registry.map_imperatively` will produce a
      :class:`_orm.Mapper` for a class without scanning the class for
      declarative class attributes. This method suits the use case historically
      provided by the ``sqlalchemy.orm.mapper()`` classical mapping function,
      which is removed as of SQLAlchemy 2.0.

    .. versionadded:: 1.4

    .. seealso::

        :ref:`orm_mapping_classes_toplevel` - overview of class mapping
        styles.

    """

    _class_registry: clsregistry._ClsRegistryType
    _managers: weakref.WeakKeyDictionary[ClassManager[Any], Literal[True]]
    _non_primary_mappers: weakref.WeakKeyDictionary[Mapper[Any], Literal[True]]
    metadata: MetaData
    constructor: CallableReference[Callable[..., None]]
    type_annotation_map: _MutableTypeAnnotationMapType
    _dependents: Set[_RegistryType]
    _dependencies: Set[_RegistryType]
    _new_mappers: bool

    def __init__(
        self,
        *,
        metadata: Optional[MetaData] = None,
        class_registry: Optional[clsregistry._ClsRegistryType] = None,
        type_annotation_map: Optional[_TypeAnnotationMapType] = None,
        constructor: Callable[..., None] = _declarative_constructor,
    ):
        r"""Construct a new :class:`_orm.registry`

        :param metadata:
          An optional :class:`_schema.MetaData` instance.  All
          :class:`_schema.Table` objects generated using declarative
          table mapping will make use of this :class:`_schema.MetaData`
          collection.  If this argument is left at its default of ``None``,