827 lines
27 KiB
Python
827 lines
27 KiB
Python
# ext/declarative/api.py
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# Copyright (C) 2005-2020 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: http://www.opensource.org/licenses/mit-license.php
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"""Public API functions and helpers for declarative."""
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import re
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import weakref
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from .base import _add_attribute
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from .base import _as_declarative
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from .base import _declarative_constructor
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from .base import _DeferredMapperConfig
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from .base import _del_attribute
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from .clsregistry import _class_resolver
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from ... import exc
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from ... import inspection
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from ... import util
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from ...orm import attributes
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from ...orm import comparable_property
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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 properties
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from ...orm import synonym as _orm_synonym
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from ...orm.base import _inspect_mapped_class
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from ...orm.base import _mapper_or_none
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from ...orm.util import polymorphic_union
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from ...schema import MetaData
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from ...schema import Table
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from ...util import hybridmethod
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from ...util import hybridproperty
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from ...util import OrderedDict
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def instrument_declarative(cls, registry, metadata):
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"""Given a class, configure the class declaratively,
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using the given registry, which can be any dictionary, and
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MetaData object.
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"""
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if "_decl_class_registry" in cls.__dict__:
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raise exc.InvalidRequestError(
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"Class %r already has been " "instrumented declaratively" % cls
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)
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cls._decl_class_registry = registry
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cls.metadata = metadata
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_as_declarative(cls, cls.__name__, cls.__dict__)
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def has_inherited_table(cls):
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"""Given a class, return True if any of the classes it inherits from has a
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mapped table, otherwise return False.
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This is used in declarative mixins to build attributes that behave
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differently for the base class vs. a subclass in an inheritance
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hierarchy.
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.. seealso::
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:ref:`decl_mixin_inheritance`
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"""
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for class_ in cls.__mro__[1:]:
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if getattr(class_, "__table__", None) is not None:
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return True
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return False
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class DeclarativeMeta(type):
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def __init__(cls, classname, bases, dict_):
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if "_decl_class_registry" not in cls.__dict__:
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_as_declarative(cls, classname, cls.__dict__)
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type.__init__(cls, classname, bases, dict_)
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def __setattr__(cls, key, value):
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_add_attribute(cls, key, value)
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def __delattr__(cls, key):
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_del_attribute(cls, key)
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def synonym_for(name, map_column=False):
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"""Decorator that produces an :func:`.orm.synonym` attribute in conjunction
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with a Python descriptor.
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The function being decorated is passed to :func:`.orm.synonym` as the
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:paramref:`.orm.synonym.descriptor` parameter::
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class MyClass(Base):
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__tablename__ = 'my_table'
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id = Column(Integer, primary_key=True)
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_job_status = Column("job_status", String(50))
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@synonym_for("job_status")
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@property
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def job_status(self):
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return "Status: %s" % self._job_status
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The :ref:`hybrid properties <mapper_hybrids>` feature of SQLAlchemy
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is typically preferred instead of synonyms, which is a more legacy
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feature.
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.. seealso::
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:ref:`synonyms` - Overview of synonyms
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:func:`.orm.synonym` - the mapper-level function
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:ref:`mapper_hybrids` - The Hybrid Attribute extension provides an
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updated approach to augmenting attribute behavior more flexibly than
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can be achieved with synonyms.
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"""
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def decorate(fn):
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return _orm_synonym(name, map_column=map_column, descriptor=fn)
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return decorate
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def comparable_using(comparator_factory):
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"""Decorator, allow a Python @property to be used in query criteria.
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This is a decorator front end to
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:func:`~sqlalchemy.orm.comparable_property` that passes
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through the comparator_factory and the function being decorated::
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@comparable_using(MyComparatorType)
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@property
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def prop(self):
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return 'special sauce'
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The regular ``comparable_property()`` is also usable directly in a
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declarative setting and may be convenient for read/write properties::
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prop = comparable_property(MyComparatorType)
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"""
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def decorate(fn):
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return comparable_property(comparator_factory, fn)
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return decorate
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class declared_attr(interfaces._MappedAttribute, property):
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"""Mark a class-level method as representing the definition of
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a mapped property or special declarative member name.
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@declared_attr turns the attribute into a scalar-like
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property that can be invoked from the uninstantiated class.
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Declarative treats attributes specifically marked with
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@declared_attr as returning a construct that is specific
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to mapping or declarative table configuration. The name
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of the attribute is that of what the non-dynamic version
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of the attribute would be.
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@declared_attr is more often than not applicable to mixins,
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to define relationships that are to be applied to different
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implementors of the class::
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class ProvidesUser(object):
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"A mixin that adds a 'user' relationship to classes."
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@declared_attr
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def user(self):
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return relationship("User")
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It also can be applied to mapped classes, such as to provide
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a "polymorphic" scheme for inheritance::
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class Employee(Base):
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id = Column(Integer, primary_key=True)
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type = Column(String(50), nullable=False)
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@declared_attr
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def __tablename__(cls):
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return cls.__name__.lower()
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@declared_attr
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def __mapper_args__(cls):
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if cls.__name__ == 'Employee':
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return {
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"polymorphic_on":cls.type,
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"polymorphic_identity":"Employee"
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}
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else:
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return {"polymorphic_identity":cls.__name__}
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"""
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def __init__(self, fget, cascading=False):
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super(declared_attr, self).__init__(fget)
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self.__doc__ = fget.__doc__
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self._cascading = cascading
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def __get__(desc, self, cls):
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reg = cls.__dict__.get("_sa_declared_attr_reg", None)
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if reg is None:
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if (
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not re.match(r"^__.+__$", desc.fget.__name__)
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and attributes.manager_of_class(cls) is None
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):
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util.warn(
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"Unmanaged access of declarative attribute %s from "
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"non-mapped class %s" % (desc.fget.__name__, cls.__name__)
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)
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return desc.fget(cls)
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elif desc in reg:
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return reg[desc]
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else:
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reg[desc] = obj = desc.fget(cls)
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return obj
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@hybridmethod
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def _stateful(cls, **kw):
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return _stateful_declared_attr(**kw)
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@hybridproperty
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def cascading(cls):
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"""Mark a :class:`.declared_attr` as cascading.
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This is a special-use modifier which indicates that a column
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or MapperProperty-based declared attribute should be configured
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distinctly per mapped subclass, within a mapped-inheritance scenario.
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.. warning::
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The :attr:`.declared_attr.cascading` modifier has several
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limitations:
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* The flag **only** applies to the use of :class:`.declared_attr`
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on declarative mixin classes and ``__abstract__`` classes; it
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currently has no effect when used on a mapped class directly.
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* The flag **only** applies to normally-named attributes, e.g.
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not any special underscore attributes such as ``__tablename__``.
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On these attributes it has **no** effect.
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* The flag currently **does not allow further overrides** down
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the class hierarchy; if a subclass tries to override the
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attribute, a warning is emitted and the overridden attribute
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is skipped. This is a limitation that it is hoped will be
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resolved at some point.
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Below, both MyClass as well as MySubClass will have a distinct
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``id`` Column object established::
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class HasIdMixin(object):
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@declared_attr.cascading
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def id(cls):
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if has_inherited_table(cls):
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return Column(
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ForeignKey('myclass.id'), primary_key=True)
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else:
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return Column(Integer, primary_key=True)
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class MyClass(HasIdMixin, Base):
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__tablename__ = 'myclass'
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# ...
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class MySubClass(MyClass):
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""
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# ...
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The behavior of the above configuration is that ``MySubClass``
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will refer to both its own ``id`` column as well as that of
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``MyClass`` underneath the attribute named ``some_id``.
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.. seealso::
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:ref:`declarative_inheritance`
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:ref:`mixin_inheritance_columns`
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"""
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return cls._stateful(cascading=True)
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class _stateful_declared_attr(declared_attr):
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def __init__(self, **kw):
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self.kw = kw
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def _stateful(self, **kw):
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new_kw = self.kw.copy()
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new_kw.update(kw)
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return _stateful_declared_attr(**new_kw)
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def __call__(self, fn):
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return declared_attr(fn, **self.kw)
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def declarative_base(
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bind=None,
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metadata=None,
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mapper=None,
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cls=object,
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name="Base",
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constructor=_declarative_constructor,
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class_registry=None,
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metaclass=DeclarativeMeta,
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):
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r"""Construct a base class for declarative class definitions.
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The new base class will be given a metaclass that produces
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appropriate :class:`~sqlalchemy.schema.Table` objects and makes
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the appropriate :func:`~sqlalchemy.orm.mapper` calls based on the
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information provided declaratively in the class and any subclasses
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of the class.
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:param bind: An optional
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:class:`~sqlalchemy.engine.Connectable`, will be assigned
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the ``bind`` attribute on the :class:`~sqlalchemy.schema.MetaData`
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instance.
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:param metadata:
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An optional :class:`~sqlalchemy.schema.MetaData` instance. All
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:class:`~sqlalchemy.schema.Table` objects implicitly declared by
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subclasses of the base will share this MetaData. A MetaData instance
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will be created if none is provided. The
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:class:`~sqlalchemy.schema.MetaData` instance will be available via the
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`metadata` attribute of the generated declarative base class.
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:param mapper:
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An optional callable, defaults to :func:`~sqlalchemy.orm.mapper`. Will
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be used to map subclasses to their Tables.
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:param cls:
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Defaults to :class:`object`. A type to use as the base for the generated
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declarative base class. May be a class or tuple of classes.
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:param name:
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Defaults to ``Base``. The display name for the generated
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class. Customizing this is not required, but can improve clarity in
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tracebacks and debugging.
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:param constructor:
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Defaults to
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:func:`~sqlalchemy.ext.declarative.base._declarative_constructor`, an
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__init__ implementation that assigns \**kwargs for declared
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fields and relationships to an instance. If ``None`` is supplied,
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no __init__ will be provided and construction will fall back to
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cls.__init__ by way of the normal Python semantics.
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:param class_registry: optional dictionary that will serve as the
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registry of class names-> mapped classes when string names
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are used to identify classes inside of :func:`.relationship`
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and others. Allows two or more declarative base classes
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to share the same registry of class names for simplified
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inter-base relationships.
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:param metaclass:
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Defaults to :class:`.DeclarativeMeta`. A metaclass or __metaclass__
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compatible callable to use as the meta type of the generated
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declarative base class.
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.. versionchanged:: 1.1 if :paramref:`.declarative_base.cls` is a
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single class (rather than a tuple), the constructed base class will
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inherit its docstring.
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.. seealso::
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:func:`.as_declarative`
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"""
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lcl_metadata = metadata or MetaData()
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if bind:
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lcl_metadata.bind = bind
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if class_registry is None:
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class_registry = weakref.WeakValueDictionary()
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bases = not isinstance(cls, tuple) and (cls,) or cls
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class_dict = dict(
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_decl_class_registry=class_registry, metadata=lcl_metadata
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)
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if isinstance(cls, type):
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class_dict["__doc__"] = cls.__doc__
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if constructor:
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class_dict["__init__"] = constructor
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if mapper:
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class_dict["__mapper_cls__"] = mapper
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return metaclass(name, bases, class_dict)
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def as_declarative(**kw):
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"""
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Class decorator for :func:`.declarative_base`.
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Provides a syntactical shortcut to the ``cls`` argument
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sent to :func:`.declarative_base`, allowing the base class
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to be converted in-place to a "declarative" base::
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from sqlalchemy.ext.declarative import as_declarative
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@as_declarative()
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class Base(object):
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@declared_attr
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def __tablename__(cls):
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return cls.__name__.lower()
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id = Column(Integer, primary_key=True)
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class MyMappedClass(Base):
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# ...
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All keyword arguments passed to :func:`.as_declarative` are passed
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along to :func:`.declarative_base`.
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.. seealso::
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:func:`.declarative_base`
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"""
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def decorate(cls):
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kw["cls"] = cls
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kw["name"] = cls.__name__
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return declarative_base(**kw)
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return decorate
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class ConcreteBase(object):
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"""A helper class for 'concrete' declarative mappings.
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:class:`.ConcreteBase` will use the :func:`.polymorphic_union`
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function automatically, against all tables mapped as a subclass
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to this class. The function is called via the
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``__declare_last__()`` function, which is essentially
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a hook for the :meth:`.after_configured` event.
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:class:`.ConcreteBase` produces a mapped
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table for the class itself. Compare to :class:`.AbstractConcreteBase`,
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which does not.
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Example::
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from sqlalchemy.ext.declarative import ConcreteBase
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class Employee(ConcreteBase, Base):
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__tablename__ = 'employee'
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employee_id = Column(Integer, primary_key=True)
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name = Column(String(50))
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__mapper_args__ = {
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'polymorphic_identity':'employee',
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'concrete':True}
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class Manager(Employee):
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__tablename__ = 'manager'
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employee_id = Column(Integer, primary_key=True)
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name = Column(String(50))
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manager_data = Column(String(40))
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__mapper_args__ = {
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'polymorphic_identity':'manager',
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'concrete':True}
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.. seealso::
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:class:`.AbstractConcreteBase`
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:ref:`concrete_inheritance`
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:ref:`inheritance_concrete_helpers`
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"""
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@classmethod
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def _create_polymorphic_union(cls, mappers):
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return polymorphic_union(
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OrderedDict(
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(mp.polymorphic_identity, mp.local_table) for mp in mappers
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),
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"type",
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"pjoin",
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)
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@classmethod
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def __declare_first__(cls):
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m = cls.__mapper__
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if m.with_polymorphic:
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return
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mappers = list(m.self_and_descendants)
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pjoin = cls._create_polymorphic_union(mappers)
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m._set_with_polymorphic(("*", pjoin))
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m._set_polymorphic_on(pjoin.c.type)
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class AbstractConcreteBase(ConcreteBase):
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"""A helper class for 'concrete' declarative mappings.
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:class:`.AbstractConcreteBase` will use the :func:`.polymorphic_union`
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function automatically, against all tables mapped as a subclass
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to this class. The function is called via the
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``__declare_last__()`` function, which is essentially
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a hook for the :meth:`.after_configured` event.
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:class:`.AbstractConcreteBase` does produce a mapped class
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for the base class, however it is not persisted to any table; it
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is instead mapped directly to the "polymorphic" selectable directly
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and is only used for selecting. Compare to :class:`.ConcreteBase`,
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which does create a persisted table for the base class.
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.. note::
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The :class:`.AbstractConcreteBase` class does not intend to set up the
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mapping for the base class until all the subclasses have been defined,
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as it needs to create a mapping against a selectable that will include
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all subclass tables. In order to achieve this, it waits for the
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**mapper configuration event** to occur, at which point it scans
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through all the configured subclasses and sets up a mapping that will
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query against all subclasses at once.
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While this event is normally invoked automatically, in the case of
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:class:`.AbstractConcreteBase`, it may be necessary to invoke it
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explicitly after **all** subclass mappings are defined, if the first
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operation is to be a query against this base class. To do so, invoke
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:func:`.configure_mappers` once all the desired classes have been
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configured::
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from sqlalchemy.orm import configure_mappers
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configure_mappers()
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.. seealso::
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:func:`.orm.configure_mappers`
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Example::
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from sqlalchemy.ext.declarative import AbstractConcreteBase
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class Employee(AbstractConcreteBase, Base):
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pass
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class Manager(Employee):
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__tablename__ = 'manager'
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employee_id = Column(Integer, primary_key=True)
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name = Column(String(50))
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manager_data = Column(String(40))
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__mapper_args__ = {
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'polymorphic_identity':'manager',
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'concrete':True}
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configure_mappers()
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The abstract base class is handled by declarative in a special way;
|
|
at class configuration time, it behaves like a declarative mixin
|
|
or an ``__abstract__`` base class. Once classes are configured
|
|
and mappings are produced, it then gets mapped itself, but
|
|
after all of its descendants. This is a very unique system of mapping
|
|
not found in any other SQLAlchemy system.
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|
|
|
Using this approach, we can specify columns and properties
|
|
that will take place on mapped subclasses, in the way that
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|
we normally do as in :ref:`declarative_mixins`::
|
|
|
|
class Company(Base):
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__tablename__ = 'company'
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id = Column(Integer, primary_key=True)
|
|
|
|
class Employee(AbstractConcreteBase, Base):
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employee_id = Column(Integer, primary_key=True)
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|
|
|
@declared_attr
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def company_id(cls):
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return Column(ForeignKey('company.id'))
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|
|
|
@declared_attr
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def company(cls):
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return relationship("Company")
|
|
|
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class Manager(Employee):
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__tablename__ = 'manager'
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|
|
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name = Column(String(50))
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manager_data = Column(String(40))
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|
|
|
__mapper_args__ = {
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'polymorphic_identity':'manager',
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'concrete':True}
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|
|
|
configure_mappers()
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|
|
|
When we make use of our mappings however, both ``Manager`` and
|
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``Employee`` will have an independently usable ``.company`` attribute::
|
|
|
|
session.query(Employee).filter(Employee.company.has(id=5))
|
|
|
|
.. versionchanged:: 1.0.0 - The mechanics of :class:`.AbstractConcreteBase`
|
|
have been reworked to support relationships established directly
|
|
on the abstract base, without any special configurational steps.
|
|
|
|
.. seealso::
|
|
|
|
:class:`.ConcreteBase`
|
|
|
|
:ref:`concrete_inheritance`
|
|
|
|
:ref:`inheritance_concrete_helpers`
|
|
|
|
"""
|
|
|
|
__no_table__ = True
|
|
|
|
@classmethod
|
|
def __declare_first__(cls):
|
|
cls._sa_decl_prepare_nocascade()
|
|
|
|
@classmethod
|
|
def _sa_decl_prepare_nocascade(cls):
|
|
if getattr(cls, "__mapper__", None):
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|
return
|
|
|
|
to_map = _DeferredMapperConfig.config_for_cls(cls)
|
|
|
|
# can't rely on 'self_and_descendants' here
|
|
# since technically an immediate subclass
|
|
# might not be mapped, but a subclass
|
|
# may be.
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|
mappers = []
|
|
stack = list(cls.__subclasses__())
|
|
while stack:
|
|
klass = stack.pop()
|
|
stack.extend(klass.__subclasses__())
|
|
mn = _mapper_or_none(klass)
|
|
if mn is not None:
|
|
mappers.append(mn)
|
|
pjoin = cls._create_polymorphic_union(mappers)
|
|
|
|
# For columns that were declared on the class, these
|
|
# are normally ignored with the "__no_table__" mapping,
|
|
# unless they have a different attribute key vs. col name
|
|
# and are in the properties argument.
|
|
# In that case, ensure we update the properties entry
|
|
# to the correct column from the pjoin target table.
|
|
declared_cols = set(to_map.declared_columns)
|
|
for k, v in list(to_map.properties.items()):
|
|
if v in declared_cols:
|
|
to_map.properties[k] = pjoin.c[v.key]
|
|
|
|
to_map.local_table = pjoin
|
|
|
|
m_args = to_map.mapper_args_fn or dict
|
|
|
|
def mapper_args():
|
|
args = m_args()
|
|
args["polymorphic_on"] = pjoin.c.type
|
|
return args
|
|
|
|
to_map.mapper_args_fn = mapper_args
|
|
|
|
m = to_map.map()
|
|
|
|
for scls in cls.__subclasses__():
|
|
sm = _mapper_or_none(scls)
|
|
if sm and sm.concrete and cls in scls.__bases__:
|
|
sm._set_concrete_base(m)
|
|
|
|
@classmethod
|
|
def _sa_raise_deferred_config(cls):
|
|
raise orm_exc.UnmappedClassError(
|
|
cls,
|
|
msg="Class %s is a subclass of AbstractConcreteBase and "
|
|
"has a mapping pending until all subclasses are defined. "
|
|
"Call the sqlalchemy.orm.configure_mappers() function after "
|
|
"all subclasses have been defined to "
|
|
"complete the mapping of this class."
|
|
% orm_exc._safe_cls_name(cls),
|
|
)
|
|
|
|
|
|
class DeferredReflection(object):
|
|
"""A helper class for construction of mappings based on
|
|
a deferred reflection step.
|
|
|
|
Normally, declarative can be used with reflection by
|
|
setting a :class:`.Table` object using autoload=True
|
|
as the ``__table__`` attribute on a declarative class.
|
|
The caveat is that the :class:`.Table` must be fully
|
|
reflected, or at the very least have a primary key column,
|
|
at the point at which a normal declarative mapping is
|
|
constructed, meaning the :class:`.Engine` must be available
|
|
at class declaration time.
|
|
|
|
The :class:`.DeferredReflection` mixin moves the construction
|
|
of mappers to be at a later point, after a specific
|
|
method is called which first reflects all :class:`.Table`
|
|
objects created so far. Classes can define it as such::
|
|
|
|
from sqlalchemy.ext.declarative import declarative_base
|
|
from sqlalchemy.ext.declarative import DeferredReflection
|
|
Base = declarative_base()
|
|
|
|
class MyClass(DeferredReflection, Base):
|
|
__tablename__ = 'mytable'
|
|
|
|
Above, ``MyClass`` is not yet mapped. After a series of
|
|
classes have been defined in the above fashion, all tables
|
|
can be reflected and mappings created using
|
|
:meth:`.prepare`::
|
|
|
|
engine = create_engine("someengine://...")
|
|
DeferredReflection.prepare(engine)
|
|
|
|
The :class:`.DeferredReflection` mixin can be applied to individual
|
|
classes, used as the base for the declarative base itself,
|
|
or used in a custom abstract class. Using an abstract base
|
|
allows that only a subset of classes to be prepared for a
|
|
particular prepare step, which is necessary for applications
|
|
that use more than one engine. For example, if an application
|
|
has two engines, you might use two bases, and prepare each
|
|
separately, e.g.::
|
|
|
|
class ReflectedOne(DeferredReflection, Base):
|
|
__abstract__ = True
|
|
|
|
class ReflectedTwo(DeferredReflection, Base):
|
|
__abstract__ = True
|
|
|
|
class MyClass(ReflectedOne):
|
|
__tablename__ = 'mytable'
|
|
|
|
class MyOtherClass(ReflectedOne):
|
|
__tablename__ = 'myothertable'
|
|
|
|
class YetAnotherClass(ReflectedTwo):
|
|
__tablename__ = 'yetanothertable'
|
|
|
|
# ... etc.
|
|
|
|
Above, the class hierarchies for ``ReflectedOne`` and
|
|
``ReflectedTwo`` can be configured separately::
|
|
|
|
ReflectedOne.prepare(engine_one)
|
|
ReflectedTwo.prepare(engine_two)
|
|
|
|
"""
|
|
|
|
@classmethod
|
|
def prepare(cls, engine):
|
|
"""Reflect all :class:`.Table` objects for all current
|
|
:class:`.DeferredReflection` subclasses"""
|
|
|
|
to_map = _DeferredMapperConfig.classes_for_base(cls)
|
|
for thingy in to_map:
|
|
cls._sa_decl_prepare(thingy.local_table, engine)
|
|
thingy.map()
|
|
mapper = thingy.cls.__mapper__
|
|
metadata = mapper.class_.metadata
|
|
for rel in mapper._props.values():
|
|
if (
|
|
isinstance(rel, properties.RelationshipProperty)
|
|
and rel.secondary is not None
|
|
):
|
|
if isinstance(rel.secondary, Table):
|
|
cls._reflect_table(rel.secondary, engine)
|
|
elif isinstance(rel.secondary, _class_resolver):
|
|
rel.secondary._resolvers += (
|
|
cls._sa_deferred_table_resolver(engine, metadata),
|
|
)
|
|
|
|
@classmethod
|
|
def _sa_deferred_table_resolver(cls, engine, metadata):
|
|
def _resolve(key):
|
|
t1 = Table(key, metadata)
|
|
cls._reflect_table(t1, engine)
|
|
return t1
|
|
|
|
return _resolve
|
|
|
|
@classmethod
|
|
def _sa_decl_prepare(cls, local_table, engine):
|
|
# autoload Table, which is already
|
|
# present in the metadata. This
|
|
# will fill in db-loaded columns
|
|
# into the existing Table object.
|
|
if local_table is not None:
|
|
cls._reflect_table(local_table, engine)
|
|
|
|
@classmethod
|
|
def _sa_raise_deferred_config(cls):
|
|
raise orm_exc.UnmappedClassError(
|
|
cls,
|
|
msg="Class %s is a subclass of DeferredReflection. "
|
|
"Mappings are not produced until the .prepare() "
|
|
"method is called on the class hierarchy."
|
|
% orm_exc._safe_cls_name(cls),
|
|
)
|
|
|
|
@classmethod
|
|
def _reflect_table(cls, table, engine):
|
|
Table(
|
|
table.name,
|
|
table.metadata,
|
|
extend_existing=True,
|
|
autoload_replace=False,
|
|
autoload=True,
|
|
autoload_with=engine,
|
|
schema=table.schema,
|
|
)
|
|
|
|
|
|
@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
|