JezK
Edit File: decl_api.py
# ext/declarative/api.py # Copyright (C) 2005-2023 the SQLAlchemy authors and contributors # <see AUTHORS file> # # This module is part of SQLAlchemy and is released under # the MIT License: https://www.opensource.org/licenses/mit-license.php """Public API functions and helpers for declarative.""" from __future__ import absolute_import import itertools import re import weakref from . import attributes from . import clsregistry from . import exc as orm_exc from . import instrumentation from . import interfaces from . import mapper as mapperlib from .base import _inspect_mapped_class from .decl_base import _add_attribute from .decl_base import _as_declarative from .decl_base import _declarative_constructor from .decl_base import _DeferredMapperConfig from .decl_base import _del_attribute from .decl_base import _mapper from .descriptor_props import SynonymProperty as _orm_synonym from .. import exc from .. import inspection from .. import util from ..sql.schema import MetaData from ..util import hybridmethod from ..util import hybridproperty def has_inherited_table(cls): """Given a class, return True if any of the classes it inherits from has a mapped table, otherwise return False. This is used in declarative mixins to build attributes that behave differently for the base class vs. a subclass in an inheritance hierarchy. .. seealso:: :ref:`decl_mixin_inheritance` """ for class_ in cls.__mro__[1:]: if getattr(class_, "__table__", None) is not None: return True return False class DeclarativeMeta(type): def __init__(cls, classname, bases, dict_, **kw): # use cls.__dict__, which can be modified by an # __init_subclass__() method (#7900) dict_ = cls.__dict__ # early-consume registry from the initial declarative base, # assign privately to not conflict with subclass attributes named # "registry" reg = getattr(cls, "_sa_registry", None) if reg is None: reg = dict_.get("registry", None) if not isinstance(reg, registry): raise exc.InvalidRequestError( "Declarative base class has no 'registry' attribute, " "or registry is not a sqlalchemy.orm.registry() object" ) else: cls._sa_registry = reg if not cls.__dict__.get("__abstract__", False): _as_declarative(reg, cls, dict_) type.__init__(cls, classname, bases, dict_) def __setattr__(cls, key, value): _add_attribute(cls, key, value) def __delattr__(cls, key): _del_attribute(cls, key) def synonym_for(name, map_column=False): """Decorator that produces an :func:`_orm.synonym` attribute in conjunction with a Python descriptor. The function being decorated is passed to :func:`_orm.synonym` as the :paramref:`.orm.synonym.descriptor` parameter:: class MyClass(Base): __tablename__ = 'my_table' id = Column(Integer, primary_key=True) _job_status = Column("job_status", String(50)) @synonym_for("job_status") @property def job_status(self): return "Status: %s" % self._job_status The :ref:`hybrid properties <mapper_hybrids>` feature of SQLAlchemy is typically preferred instead of synonyms, which is a more legacy feature. .. seealso:: :ref:`synonyms` - Overview of synonyms :func:`_orm.synonym` - the mapper-level function :ref:`mapper_hybrids` - The Hybrid Attribute extension provides an updated approach to augmenting attribute behavior more flexibly than can be achieved with synonyms. """ def decorate(fn): return _orm_synonym(name, map_column=map_column, descriptor=fn) return decorate class declared_attr(interfaces._MappedAttribute, property): """Mark a class-level method as representing the definition of a mapped property or special declarative member name. :class:`_orm.declared_attr` is typically applied as a decorator to a class level method, turning the attribute into a scalar-like property that can be invoked from the uninstantiated class. The Declarative mapping process looks for these :class:`_orm.declared_attr` callables as it scans classes, and assumes any attribute marked with :class:`_orm.declared_attr` will be a callable that will produce an object specific to the Declarative mapping or table configuration. :class:`_orm.declared_attr` is usually applicable to mixins, to define relationships that are to be applied to different implementors of the class. It is also used to define :class:`_schema.Column` objects that include the :class:`_schema.ForeignKey` construct, as these cannot be easily reused across different mappings. The example below illustrates both:: class ProvidesUser(object): "A mixin that adds a 'user' relationship to classes." @declared_attr def user_id(self): return Column(ForeignKey("user_account.id")) @declared_attr def user(self): return relationship("User") :class:`_orm.declared_attr` can also be applied to mapped classes, such as to provide a "polymorphic" scheme for inheritance:: class Employee(Base): id = Column(Integer, primary_key=True) type = Column(String(50), nullable=False) @declared_attr def __tablename__(cls): return cls.__name__.lower() @declared_attr def __mapper_args__(cls): if cls.__name__ == 'Employee': return { "polymorphic_on":cls.type, "polymorphic_identity":"Employee" } else: return {"polymorphic_identity":cls.__name__} To use :class:`_orm.declared_attr` inside of a Python dataclass as discussed at :ref:`orm_declarative_dataclasses_declarative_table`, it may be placed directly inside the field metadata using a lambda:: @dataclass class AddressMixin: __sa_dataclass_metadata_key__ = "sa" user_id: int = field( init=False, metadata={"sa": declared_attr(lambda: Column(ForeignKey("user.id")))} ) user: User = field( init=False, metadata={"sa": declared_attr(lambda: relationship(User))} ) :class:`_orm.declared_attr` also may be omitted from this form using a lambda directly, as in:: user: User = field( init=False, metadata={"sa": lambda: relationship(User)} ) .. seealso:: :ref:`orm_mixins_toplevel` - illustrates how to use Declarative Mixins which is the primary use case for :class:`_orm.declared_attr` :ref:`orm_declarative_dataclasses_mixin` - illustrates special forms for use with Python dataclasses """ # noqa: E501 def __init__(self, fget, cascading=False): super(declared_attr, self).__init__(fget) self.__doc__ = fget.__doc__ self._cascading = cascading def __get__(desc, self, cls): # the declared_attr needs to make use of a cache that exists # for the span of the declarative scan_attributes() phase. # to achieve this we look at the class manager that's configured. manager = attributes.manager_of_class(cls) if manager is None: if not re.match(r"^__.+__$", desc.fget.__name__): # if there is no manager at all, then this class hasn't been # run through declarative or mapper() at all, emit a warning. util.warn( "Unmanaged access of declarative attribute %s from " "non-mapped class %s" % (desc.fget.__name__, cls.__name__) ) return desc.fget(cls) elif manager.is_mapped: # the class is mapped, which means we're outside of the declarative # scan setup, just run the function. return desc.fget(cls) # here, we are inside of the declarative scan. use the registry # that is tracking the values of these attributes. declarative_scan = manager.declarative_scan() assert declarative_scan is not None reg = declarative_scan.declared_attr_reg if desc in reg: return reg[desc] else: reg[desc] = obj = desc.fget(cls) return obj @hybridmethod def _stateful(cls, **kw): return _stateful_declared_attr(**kw) @hybridproperty def cascading(cls): """Mark a :class:`.declared_attr` as cascading. This is a special-use modifier which indicates that a column or MapperProperty-based declared attribute should be configured distinctly per mapped subclass, within a mapped-inheritance scenario. .. warning:: The :attr:`.declared_attr.cascading` modifier has several limitations: * The flag **only** applies to the use of :class:`.declared_attr` on declarative mixin classes and ``__abstract__`` classes; it currently has no effect when used on a mapped class directly. * The flag **only** applies to normally-named attributes, e.g. not any special underscore attributes such as ``__tablename__``. On these attributes it has **no** effect. * The flag currently **does not allow further overrides** down the class hierarchy; if a subclass tries to override the attribute, a warning is emitted and the overridden attribute is skipped. This is a limitation that it is hoped will be resolved at some point. Below, both MyClass as well as MySubClass will have a distinct ``id`` Column object established:: class HasIdMixin(object): @declared_attr.cascading def id(cls): if has_inherited_table(cls): return Column( ForeignKey('myclass.id'), primary_key=True ) else: return Column(Integer, primary_key=True) class MyClass(HasIdMixin, Base): __tablename__ = 'myclass' # ... class MySubClass(MyClass): "" # ... The behavior of the above configuration is that ``MySubClass`` will refer to both its own ``id`` column as well as that of ``MyClass`` underneath the attribute named ``some_id``. .. seealso:: :ref:`declarative_inheritance` :ref:`mixin_inheritance_columns` """ return cls._stateful(cascading=True) class _stateful_declared_attr(declared_attr): def __init__(self, **kw): self.kw = kw def _stateful(self, **kw): new_kw = self.kw.copy() new_kw.update(kw) return _stateful_declared_attr(**new_kw) def __call__(self, fn): return declared_attr(fn, **self.kw) def declarative_mixin(cls): """Mark a class as providing the feature of "declarative mixin". E.g.:: from sqlalchemy.orm import declared_attr from sqlalchemy.orm import declarative_mixin @declarative_mixin class MyMixin: @declared_attr def __tablename__(cls): return cls.__name__.lower() __table_args__ = {'mysql_engine': 'InnoDB'} __mapper_args__= {'always_refresh': True} id = Column(Integer, primary_key=True) class MyModel(MyMixin, Base): name = Column(String(1000)) The :func:`_orm.declarative_mixin` decorator currently does not modify the given class in any way; it's current purpose is strictly to assist the :ref:`Mypy plugin <mypy_toplevel>` in being able to identify SQLAlchemy declarative mixin classes when no other context is present. .. versionadded:: 1.4.6 .. seealso:: :ref:`orm_mixins_toplevel` :ref:`mypy_declarative_mixins` - in the :ref:`Mypy plugin documentation <mypy_toplevel>` """ # noqa: E501 return cls def declarative_base( bind=None, metadata=None, mapper=None, cls=object, name="Base", constructor=_declarative_constructor, class_registry=None, metaclass=DeclarativeMeta, ): r"""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 :func:`~sqlalchemy.orm.mapper` calls based on the information provided declaratively in the class and any subclasses of the class. 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 bind: An optional :class:`~sqlalchemy.engine.Connectable`, will be assigned the ``bind`` attribute on the :class:`~sqlalchemy.schema.MetaData` instance. .. deprecated:: 1.4 The "bind" argument to declarative_base is deprecated and will be removed in SQLAlchemy 2.0. :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 :func:`~sqlalchemy.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 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` """ if bind is not None: # util.deprecated_params does not work util.warn_deprecated_20( "The ``bind`` argument to declarative_base is " "deprecated and will be removed in SQLAlchemy 2.0.", ) return registry( _bind=bind, metadata=metadata, class_registry=class_registry, constructor=constructor, ).generate_base( mapper=mapper, cls=cls, name=name, metaclass=metaclass, ) class registry(object): """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 :func:`_orm.mapper` classical mapping function. .. versionadded:: 1.4 .. seealso:: :ref:`orm_mapping_classes_toplevel` - overview of class mapping styles. """ def __init__( self, metadata=None, class_registry=None, constructor=_declarative_constructor, _bind=None, ): 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``, a blank :class:`_schema.MetaData` collection is created. :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. """ lcl_metadata = metadata or MetaData() if _bind: lcl_metadata.bind = _bind if class_registry is None: class_registry = weakref.WeakValueDictionary() self._class_registry = class_registry self._managers = weakref.WeakKeyDictionary() self._non_primary_mappers = weakref.WeakKeyDictionary() self.metadata = lcl_metadata self.constructor = constructor self._dependents = set() self._dependencies = set() self._new_mappers = False with mapperlib._CONFIGURE_MUTEX: mapperlib._mapper_registries[self] = True @property def mappers(self): """read only collection of all :class:`_orm.Mapper` objects.""" return frozenset(manager.mapper for manager in self._managers).union( self._non_primary_mappers ) def _set_depends_on(self, registry): if registry is self: return registry._dependents.add(self) self._dependencies.add(registry) def _flag_new_mapper(self, mapper): mapper._ready_for_configure = True if self._new_mappers: return for reg in self._recurse_with_dependents({self}): reg._new_mappers = True @classmethod def _recurse_with_dependents(cls, registries): todo = registries done = set() while todo: reg = todo.pop() done.add(reg) # if yielding would remove dependents, make sure we have # them before todo.update(reg._dependents.difference(done)) yield reg # if yielding would add dependents, make sure we have them # after todo.update(reg._dependents.difference(done)) @classmethod def _recurse_with_dependencies(cls, registries): todo = registries done = set() while todo: reg = todo.pop() done.add(reg) # if yielding would remove dependencies, make sure we have # them before todo.update(reg._dependencies.difference(done)) yield reg # if yielding would remove dependencies, make sure we have # them before todo.update(reg._dependencies.difference(done)) def _mappers_to_configure(self): return itertools.chain( ( manager.mapper for manager in list(self._managers) if manager.is_mapped and not manager.mapper.configured and manager.mapper._ready_for_configure ), ( npm for npm in list(self._non_primary_mappers) if not npm.configured and npm._ready_for_configure ), ) def _add_non_primary_mapper(self, np_mapper): self._non_primary_mappers[np_mapper] = True def _dispose_cls(self, cls): clsregistry.remove_class(cls.__name__, cls, self._class_registry) def _add_manager(self, manager): self._managers[manager] = True if manager.registry is not None and manager.is_mapped: raise exc.ArgumentError( "Class '%s' already has a primary mapper defined. " % manager.class_ ) manager.registry = self def configure(self, cascade=False): """Configure all as-yet unconfigured mappers in this :class:`_orm.registry`. The configure step is used to reconcile and initialize the :func:`_orm.relationship` linkages between mapped classes, as well as to invoke configuration events such as the :meth:`_orm.MapperEvents.before_configured` and :meth:`_orm.MapperEvents.after_configured`, which may be used by ORM extensions or user-defined extension hooks. If one or more mappers in this registry contain :func:`_orm.relationship` constructs that refer to mapped classes in other registries, this registry is said to be *dependent* on those registries. In order to configure those dependent registries automatically, the :paramref:`_orm.registry.configure.cascade` flag should be set to ``True``. Otherwise, if they are not configured, an exception will be raised. The rationale behind this behavior is to allow an application to programmatically invoke configuration of registries while controlling whether or not the process implicitly reaches other registries. As an alternative to invoking :meth:`_orm.registry.configure`, the ORM function :func:`_orm.configure_mappers` function may be used to ensure configuration is complete for all :class:`_orm.registry` objects in memory. This is generally simpler to use and also predates the usage of :class:`_orm.registry` objects overall. However, this function will impact all mappings throughout the running Python process and may be more memory/time consuming for an application that has many registries in use for different purposes that may not be needed immediately. .. seealso:: :func:`_orm.configure_mappers` .. versionadded:: 1.4.0b2 """ mapperlib._configure_registries({self}, cascade=cascade) def dispose(self, cascade=False): """Dispose of all mappers in this :class:`_orm.registry`. After invocation, all the classes that were mapped within this registry will no longer have class instrumentation associated with them. This method is the per-:class:`_orm.registry` analogue to the application-wide :func:`_orm.clear_mappers` function. If this registry contains mappers that are dependencies of other registries, typically via :func:`_orm.relationship` links, then those registries must be disposed as well. When such registries exist in relation to this one, their :meth:`_orm.registry.dispose` method will also be called, if the :paramref:`_orm.registry.dispose.cascade` flag is set to ``True``; otherwise, an error is raised if those registries were not already disposed. .. versionadded:: 1.4.0b2 .. seealso:: :func:`_orm.clear_mappers` """ mapperlib._dispose_registries({self}, cascade=cascade) def _dispose_manager_and_mapper(self, manager): if "mapper" in manager.__dict__: mapper = manager.mapper mapper._set_dispose_flags() class_ = manager.class_ self._dispose_cls(class_) instrumentation._instrumentation_factory.unregister(class_) def generate_base( self, mapper=None, cls=object, name="Base", metaclass=DeclarativeMeta, ): """Generate a declarative base class. Classes that inherit from the returned class object will be automatically mapped using declarative mapping. E.g.:: from sqlalchemy.orm import registry mapper_registry = registry() Base = mapper_registry.generate_base() class MyClass(Base): __tablename__ = "my_table" id = Column(Integer, primary_key=True) The above dynamically generated class is equivalent to the non-dynamic example below:: from sqlalchemy.orm import registry from sqlalchemy.orm.decl_api import DeclarativeMeta mapper_registry = registry() class Base(metaclass=DeclarativeMeta): __abstract__ = True registry = mapper_registry metadata = mapper_registry.metadata __init__ = mapper_registry.constructor The :meth:`_orm.registry.generate_base` method provides the implementation for the :func:`_orm.declarative_base` function, which creates the :class:`_orm.registry` and base class all at once. See the section :ref:`orm_declarative_mapping` for background and examples. :param mapper: An optional callable, defaults to :func:`~sqlalchemy.orm.mapper`. This function is used to generate new :class:`_orm.Mapper` objects. :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 metaclass: Defaults to :class:`.DeclarativeMeta`. A metaclass or __metaclass__ compatible callable to use as the meta type of the generated declarative base class. .. seealso:: :ref:`orm_declarative_mapping` :func:`_orm.declarative_base` """ metadata = self.metadata bases = not isinstance(cls, tuple) and (cls,) or cls class_dict = dict(registry=self, metadata=metadata) if isinstance(cls, type): class_dict["__doc__"] = cls.__doc__ if self.constructor: class_dict["__init__"] = self.constructor class_dict["__abstract__"] = True if mapper: class_dict["__mapper_cls__"] = mapper if hasattr(cls, "__class_getitem__"): def __class_getitem__(cls, key): # allow generic classes in py3.9+ return cls class_dict["__class_getitem__"] = __class_getitem__ return metaclass(name, bases, class_dict) def mapped(self, cls): """Class decorator that will apply the Declarative mapping process to a given class. E.g.:: from sqlalchemy.orm import registry mapper_registry = registry() @mapper_registry.mapped class Foo: __tablename__ = 'some_table' id = Column(Integer, primary_key=True) name = Column(String) See the section :ref:`orm_declarative_mapping` for complete details and examples. :param cls: class to be mapped. :return: the class that was passed. .. seealso:: :ref:`orm_declarative_mapping` :meth:`_orm.registry.generate_base` - generates a base class that will apply Declarative mapping to subclasses automatically using a Python metaclass. """ _as_declarative(self, cls, cls.__dict__) return cls def as_declarative_base(self, **kw): """ Class decorator which will invoke :meth:`_orm.registry.generate_base` for a given base class. E.g.:: from sqlalchemy.orm import registry mapper_registry = registry() @mapper_registry.as_declarative_base() class Base(object): @declared_attr def __tablename__(cls): return cls.__name__.lower() id = Column(Integer, primary_key=True) class MyMappedClass(Base): # ... All keyword arguments passed to :meth:`_orm.registry.as_declarative_base` are passed along to :meth:`_orm.registry.generate_base`. """ def decorate(cls): kw["cls"] = cls kw["name"] = cls.__name__ return self.generate_base(**kw) return decorate def map_declaratively(self, cls): """Map a class declaratively. In this form of mapping, the class is scanned for mapping information, including for columns to be associated with a table, and/or an actual table object. Returns the :class:`_orm.Mapper` object. E.g.:: from sqlalchemy.orm import registry mapper_registry = registry() class Foo: __tablename__ = 'some_table' id = Column(Integer, primary_key=True) name = Column(String) mapper = mapper_registry.map_declaratively(Foo) This function is more conveniently invoked indirectly via either the :meth:`_orm.registry.mapped` class decorator or by subclassing a declarative metaclass generated from :meth:`_orm.registry.generate_base`. See the section :ref:`orm_declarative_mapping` for complete details and examples. :param cls: class to be mapped. :return: a :class:`_orm.Mapper` object. .. seealso:: :ref:`orm_declarative_mapping` :meth:`_orm.registry.mapped` - more common decorator interface to this function. :meth:`_orm.registry.map_imperatively` """ return _as_declarative(self, cls, cls.__dict__) def map_imperatively(self, class_, local_table=None, **kw): r"""Map a class imperatively. In this form of mapping, the class is not scanned for any mapping information. Instead, all mapping constructs are passed as arguments. This method is intended to be fully equivalent to the classic SQLAlchemy :func:`_orm.mapper` function, except that it's in terms of a particular registry. E.g.:: from sqlalchemy.orm import registry mapper_registry = registry() my_table = Table( "my_table", mapper_registry.metadata, Column('id', Integer, primary_key=True) ) class MyClass: pass mapper_registry.map_imperatively(MyClass, my_table) See the section :ref:`orm_imperative_mapping` for complete background and usage examples. :param class\_: The class to be mapped. Corresponds to the :paramref:`_orm.mapper.class_` parameter. :param local_table: the :class:`_schema.Table` or other :class:`_sql.FromClause` object that is the subject of the mapping. Corresponds to the :paramref:`_orm.mapper.local_table` parameter. :param \**kw: all other keyword arguments are passed to the :func:`_orm.mapper` function directly. .. seealso:: :ref:`orm_imperative_mapping` :ref:`orm_declarative_mapping` """ return _mapper(self, class_, local_table, kw) mapperlib._legacy_registry = registry() @util.deprecated_params( bind=( "2.0", "The ``bind`` argument to as_declarative is " "deprecated and will be removed in SQLAlchemy 2.0.", ) ) def as_declarative(**kw): """ Class decorator which will adapt a given class into a :func:`_orm.declarative_base`. This function makes use of the :meth:`_orm.registry.as_declarative_base` method, by first creating a :class:`_orm.registry` automatically and then invoking the decorator. E.g.:: from sqlalchemy.orm import as_declarative @as_declarative() class Base(object): @declared_attr def __tablename__(cls): return cls.__name__.lower() id = Column(Integer, primary_key=True) class MyMappedClass(Base): # ... .. seealso:: :meth:`_orm.registry.as_declarative_base` """ bind, metadata, class_registry = ( kw.pop("bind", None), kw.pop("metadata", None), kw.pop("class_registry", None), ) return registry( _bind=bind, metadata=metadata, class_registry=class_registry ).as_declarative_base(**kw) @inspection._inspects(DeclarativeMeta) def _inspect_decl_meta(cls): mp = _inspect_mapped_class(cls) if mp is None: if _DeferredMapperConfig.has_cls(cls): _DeferredMapperConfig.raise_unmapped_for_cls(cls) raise orm_exc.UnmappedClassError( cls, msg="Class %s has a deferred mapping on it. It is not yet " "usable as a mapped class." % orm_exc._safe_cls_name(cls), ) return mp