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+# ext/associationproxy.py
+# Copyright (C) 2005-2024 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
+
+"""Contain the ``AssociationProxy`` class.
+
+The ``AssociationProxy`` is a Python property object which provides
+transparent proxied access to the endpoint of an association object.
+
+See the example ``examples/association/proxied_association.py``.
+
+"""
+from __future__ import annotations
+
+import operator
+import typing
+from typing import AbstractSet
+from typing import Any
+from typing import Callable
+from typing import cast
+from typing import Collection
+from typing import Dict
+from typing import Generic
+from typing import ItemsView
+from typing import Iterable
+from typing import Iterator
+from typing import KeysView
+from typing import List
+from typing import Mapping
+from typing import MutableMapping
+from typing import MutableSequence
+from typing import MutableSet
+from typing import NoReturn
+from typing import Optional
+from typing import overload
+from typing import Set
+from typing import Tuple
+from typing import Type
+from typing import TypeVar
+from typing import Union
+from typing import ValuesView
+
+from .. import ColumnElement
+from .. import exc
+from .. import inspect
+from .. import orm
+from .. import util
+from ..orm import collections
+from ..orm import InspectionAttrExtensionType
+from ..orm import interfaces
+from ..orm import ORMDescriptor
+from ..orm.base import SQLORMOperations
+from ..orm.interfaces import _AttributeOptions
+from ..orm.interfaces import _DCAttributeOptions
+from ..orm.interfaces import _DEFAULT_ATTRIBUTE_OPTIONS
+from ..sql import operators
+from ..sql import or_
+from ..sql.base import _NoArg
+from ..util.typing import Literal
+from ..util.typing import Protocol
+from ..util.typing import Self
+from ..util.typing import SupportsIndex
+from ..util.typing import SupportsKeysAndGetItem
+
+if typing.TYPE_CHECKING:
+    from ..orm.interfaces import MapperProperty
+    from ..orm.interfaces import PropComparator
+    from ..orm.mapper import Mapper
+    from ..sql._typing import _ColumnExpressionArgument
+    from ..sql._typing import _InfoType
+
+
+_T = TypeVar("_T", bound=Any)
+_T_co = TypeVar("_T_co", bound=Any, covariant=True)
+_T_con = TypeVar("_T_con", bound=Any, contravariant=True)
+_S = TypeVar("_S", bound=Any)
+_KT = TypeVar("_KT", bound=Any)
+_VT = TypeVar("_VT", bound=Any)
+
+
+def association_proxy(
+    target_collection: str,
+    attr: str,
+    *,
+    creator: Optional[_CreatorProtocol] = None,
+    getset_factory: Optional[_GetSetFactoryProtocol] = None,
+    proxy_factory: Optional[_ProxyFactoryProtocol] = None,
+    proxy_bulk_set: Optional[_ProxyBulkSetProtocol] = None,
+    info: Optional[_InfoType] = None,
+    cascade_scalar_deletes: bool = False,
+    create_on_none_assignment: bool = False,
+    init: Union[_NoArg, bool] = _NoArg.NO_ARG,
+    repr: Union[_NoArg, bool] = _NoArg.NO_ARG,  # noqa: A002
+    default: Optional[Any] = _NoArg.NO_ARG,
+    default_factory: Union[_NoArg, Callable[[], _T]] = _NoArg.NO_ARG,
+    compare: Union[_NoArg, bool] = _NoArg.NO_ARG,
+    kw_only: Union[_NoArg, bool] = _NoArg.NO_ARG,
+) -> AssociationProxy[Any]:
+    r"""Return a Python property implementing a view of a target
+    attribute which references an attribute on members of the
+    target.
+
+    The returned value is an instance of :class:`.AssociationProxy`.
+
+    Implements a Python property representing a relationship as a collection
+    of simpler values, or a scalar value.  The proxied property will mimic
+    the collection type of the target (list, dict or set), or, in the case of
+    a one to one relationship, a simple scalar value.
+
+    :param target_collection: Name of the attribute that is the immediate
+      target.  This attribute is typically mapped by
+      :func:`~sqlalchemy.orm.relationship` to link to a target collection, but
+      can also be a many-to-one or non-scalar relationship.
+
+    :param attr: Attribute on the associated instance or instances that
+      are available on instances of the target object.
+
+    :param creator: optional.
+
+      Defines custom behavior when new items are added to the proxied
+      collection.
+
+      By default, adding new items to the collection will trigger a
+      construction of an instance of the target object, passing the given
+      item as a positional argument to the target constructor.  For cases
+      where this isn't sufficient, :paramref:`.association_proxy.creator`
+      can supply a callable that will construct the object in the
+      appropriate way, given the item that was passed.
+
+      For list- and set- oriented collections, a single argument is
+      passed to the callable. For dictionary oriented collections, two
+      arguments are passed, corresponding to the key and value.
+
+      The :paramref:`.association_proxy.creator` callable is also invoked
+      for scalar (i.e. many-to-one, one-to-one) relationships. If the
+      current value of the target relationship attribute is ``None``, the
+      callable is used to construct a new object.  If an object value already
+      exists, the given attribute value is populated onto that object.
+
+      .. seealso::
+
+        :ref:`associationproxy_creator`
+
+    :param cascade_scalar_deletes: when True, indicates that setting
+        the proxied value to ``None``, or deleting it via ``del``, should
+        also remove the source object.  Only applies to scalar attributes.
+        Normally, removing the proxied target will not remove the proxy
+        source, as this object may have other state that is still to be
+        kept.
+
+        .. versionadded:: 1.3
+
+        .. seealso::
+
+            :ref:`cascade_scalar_deletes` - complete usage example
+
+    :param create_on_none_assignment: when True, indicates that setting
+      the proxied value to ``None`` should **create** the source object
+      if it does not exist, using the creator.  Only applies to scalar
+      attributes.  This is mutually exclusive
+      vs. the :paramref:`.assocation_proxy.cascade_scalar_deletes`.
+
+      .. versionadded:: 2.0.18
+
+    :param init: Specific to :ref:`orm_declarative_native_dataclasses`,
+     specifies if the mapped attribute should be part of the ``__init__()``
+     method as generated by the dataclass process.
+
+     .. versionadded:: 2.0.0b4
+
+    :param repr: Specific to :ref:`orm_declarative_native_dataclasses`,
+     specifies if the attribute established by this :class:`.AssociationProxy`
+     should be part of the ``__repr__()`` method as generated by the dataclass
+     process.
+
+     .. versionadded:: 2.0.0b4
+
+    :param default_factory: Specific to
+     :ref:`orm_declarative_native_dataclasses`, specifies a default-value
+     generation function that will take place as part of the ``__init__()``
+     method as generated by the dataclass process.
+
+     .. versionadded:: 2.0.0b4
+
+    :param compare: Specific to
+     :ref:`orm_declarative_native_dataclasses`, indicates if this field
+     should be included in comparison operations when generating the
+     ``__eq__()`` and ``__ne__()`` methods for the mapped class.
+
+     .. versionadded:: 2.0.0b4
+
+    :param kw_only: Specific to :ref:`orm_declarative_native_dataclasses`,
+     indicates if this field should be marked as keyword-only when generating
+     the ``__init__()`` method as generated by the dataclass process.
+
+     .. versionadded:: 2.0.0b4
+
+    :param info: optional, will be assigned to
+     :attr:`.AssociationProxy.info` if present.
+
+
+    The following additional parameters involve injection of custom behaviors
+    within the :class:`.AssociationProxy` object and are for advanced use
+    only:
+
+    :param getset_factory: Optional.  Proxied attribute access is
+        automatically handled by routines that get and set values based on
+        the `attr` argument for this proxy.
+
+        If you would like to customize this behavior, you may supply a
+        `getset_factory` callable that produces a tuple of `getter` and
+        `setter` functions.  The factory is called with two arguments, the
+        abstract type of the underlying collection and this proxy instance.
+
+    :param proxy_factory: Optional.  The type of collection to emulate is
+        determined by sniffing the target collection.  If your collection
+        type can't be determined by duck typing or you'd like to use a
+        different collection implementation, you may supply a factory
+        function to produce those collections.  Only applicable to
+        non-scalar relationships.
+
+    :param proxy_bulk_set: Optional, use with proxy_factory.
+
+
+    """
+    return AssociationProxy(
+        target_collection,
+        attr,
+        creator=creator,
+        getset_factory=getset_factory,
+        proxy_factory=proxy_factory,
+        proxy_bulk_set=proxy_bulk_set,
+        info=info,
+        cascade_scalar_deletes=cascade_scalar_deletes,
+        create_on_none_assignment=create_on_none_assignment,
+        attribute_options=_AttributeOptions(
+            init, repr, default, default_factory, compare, kw_only
+        ),
+    )
+
+
+class AssociationProxyExtensionType(InspectionAttrExtensionType):
+    ASSOCIATION_PROXY = "ASSOCIATION_PROXY"
+    """Symbol indicating an :class:`.InspectionAttr` that's
+    of type :class:`.AssociationProxy`.
+
+    Is assigned to the :attr:`.InspectionAttr.extension_type`
+    attribute.
+
+    """
+
+
+class _GetterProtocol(Protocol[_T_co]):
+    def __call__(self, instance: Any) -> _T_co: ...
+
+
+# mypy 0.990 we are no longer allowed to make this Protocol[_T_con]
+class _SetterProtocol(Protocol): ...
+
+
+class _PlainSetterProtocol(_SetterProtocol, Protocol[_T_con]):
+    def __call__(self, instance: Any, value: _T_con) -> None: ...
+
+
+class _DictSetterProtocol(_SetterProtocol, Protocol[_T_con]):
+    def __call__(self, instance: Any, key: Any, value: _T_con) -> None: ...
+
+
+# mypy 0.990 we are no longer allowed to make this Protocol[_T_con]
+class _CreatorProtocol(Protocol): ...
+
+
+class _PlainCreatorProtocol(_CreatorProtocol, Protocol[_T_con]):
+    def __call__(self, value: _T_con) -> Any: ...
+
+
+class _KeyCreatorProtocol(_CreatorProtocol, Protocol[_T_con]):
+    def __call__(self, key: Any, value: Optional[_T_con]) -> Any: ...
+
+
+class _LazyCollectionProtocol(Protocol[_T]):
+    def __call__(
+        self,
+    ) -> Union[
+        MutableSet[_T], MutableMapping[Any, _T], MutableSequence[_T]
+    ]: ...
+
+
+class _GetSetFactoryProtocol(Protocol):
+    def __call__(
+        self,
+        collection_class: Optional[Type[Any]],
+        assoc_instance: AssociationProxyInstance[Any],
+    ) -> Tuple[_GetterProtocol[Any], _SetterProtocol]: ...
+
+
+class _ProxyFactoryProtocol(Protocol):
+    def __call__(
+        self,
+        lazy_collection: _LazyCollectionProtocol[Any],
+        creator: _CreatorProtocol,
+        value_attr: str,
+        parent: AssociationProxyInstance[Any],
+    ) -> Any: ...
+
+
+class _ProxyBulkSetProtocol(Protocol):
+    def __call__(
+        self, proxy: _AssociationCollection[Any], collection: Iterable[Any]
+    ) -> None: ...
+
+
+class _AssociationProxyProtocol(Protocol[_T]):
+    """describes the interface of :class:`.AssociationProxy`
+    without including descriptor methods in the interface."""
+
+    creator: Optional[_CreatorProtocol]
+    key: str
+    target_collection: str
+    value_attr: str
+    cascade_scalar_deletes: bool
+    create_on_none_assignment: bool
+    getset_factory: Optional[_GetSetFactoryProtocol]
+    proxy_factory: Optional[_ProxyFactoryProtocol]
+    proxy_bulk_set: Optional[_ProxyBulkSetProtocol]
+
+    @util.ro_memoized_property
+    def info(self) -> _InfoType: ...
+
+    def for_class(
+        self, class_: Type[Any], obj: Optional[object] = None
+    ) -> AssociationProxyInstance[_T]: ...
+
+    def _default_getset(
+        self, collection_class: Any
+    ) -> Tuple[_GetterProtocol[Any], _SetterProtocol]: ...
+
+
+class AssociationProxy(
+    interfaces.InspectionAttrInfo,
+    ORMDescriptor[_T],
+    _DCAttributeOptions,
+    _AssociationProxyProtocol[_T],
+):
+    """A descriptor that presents a read/write view of an object attribute."""
+
+    is_attribute = True
+    extension_type = AssociationProxyExtensionType.ASSOCIATION_PROXY
+
+    def __init__(
+        self,
+        target_collection: str,
+        attr: str,
+        *,
+        creator: Optional[_CreatorProtocol] = None,
+        getset_factory: Optional[_GetSetFactoryProtocol] = None,
+        proxy_factory: Optional[_ProxyFactoryProtocol] = None,
+        proxy_bulk_set: Optional[_ProxyBulkSetProtocol] = None,
+        info: Optional[_InfoType] = None,
+        cascade_scalar_deletes: bool = False,
+        create_on_none_assignment: bool = False,
+        attribute_options: Optional[_AttributeOptions] = None,
+    ):
+        """Construct a new :class:`.AssociationProxy`.
+
+        The :class:`.AssociationProxy` object is typically constructed using
+        the :func:`.association_proxy` constructor function. See the
+        description of :func:`.association_proxy` for a description of all
+        parameters.
+
+
+        """
+        self.target_collection = target_collection
+        self.value_attr = attr
+        self.creator = creator
+        self.getset_factory = getset_factory
+        self.proxy_factory = proxy_factory
+        self.proxy_bulk_set = proxy_bulk_set
+
+        if cascade_scalar_deletes and create_on_none_assignment:
+            raise exc.ArgumentError(
+                "The cascade_scalar_deletes and create_on_none_assignment "
+                "parameters are mutually exclusive."
+            )
+        self.cascade_scalar_deletes = cascade_scalar_deletes
+        self.create_on_none_assignment = create_on_none_assignment
+
+        self.key = "_%s_%s_%s" % (
+            type(self).__name__,
+            target_collection,
+            id(self),
+        )
+        if info:
+            self.info = info  # type: ignore
+
+        if (
+            attribute_options
+            and attribute_options != _DEFAULT_ATTRIBUTE_OPTIONS
+        ):
+            self._has_dataclass_arguments = True
+            self._attribute_options = attribute_options
+        else:
+            self._has_dataclass_arguments = False
+            self._attribute_options = _DEFAULT_ATTRIBUTE_OPTIONS
+
+    @overload
+    def __get__(
+        self, instance: Literal[None], owner: Literal[None]
+    ) -> Self: ...
+
+    @overload
+    def __get__(
+        self, instance: Literal[None], owner: Any
+    ) -> AssociationProxyInstance[_T]: ...
+
+    @overload
+    def __get__(self, instance: object, owner: Any) -> _T: ...
+
+    def __get__(
+        self, instance: object, owner: Any
+    ) -> Union[AssociationProxyInstance[_T], _T, AssociationProxy[_T]]:
+        if owner is None:
+            return self
+        inst = self._as_instance(owner, instance)
+        if inst:
+            return inst.get(instance)
+
+        assert instance is None
+
+        return self
+
+    def __set__(self, instance: object, values: _T) -> None:
+        class_ = type(instance)
+        self._as_instance(class_, instance).set(instance, values)
+
+    def __delete__(self, instance: object) -> None:
+        class_ = type(instance)
+        self._as_instance(class_, instance).delete(instance)
+
+    def for_class(
+        self, class_: Type[Any], obj: Optional[object] = None
+    ) -> AssociationProxyInstance[_T]:
+        r"""Return the internal state local to a specific mapped class.
+
+        E.g., given a class ``User``::
+
+            class User(Base):
+                # ...
+
+                keywords = association_proxy('kws', 'keyword')
+
+        If we access this :class:`.AssociationProxy` from
+        :attr:`_orm.Mapper.all_orm_descriptors`, and we want to view the
+        target class for this proxy as mapped by ``User``::
+
+            inspect(User).all_orm_descriptors["keywords"].for_class(User).target_class
+
+        This returns an instance of :class:`.AssociationProxyInstance` that
+        is specific to the ``User`` class.   The :class:`.AssociationProxy`
+        object remains agnostic of its parent class.
+
+        :param class\_: the class that we are returning state for.
+
+        :param obj: optional, an instance of the class that is required
+         if the attribute refers to a polymorphic target, e.g. where we have
+         to look at the type of the actual destination object to get the
+         complete path.
+
+        .. versionadded:: 1.3 - :class:`.AssociationProxy` no longer stores
+           any state specific to a particular parent class; the state is now
+           stored in per-class :class:`.AssociationProxyInstance` objects.
+
+
+        """
+        return self._as_instance(class_, obj)
+
+    def _as_instance(
+        self, class_: Any, obj: Any
+    ) -> AssociationProxyInstance[_T]:
+        try:
+            inst = class_.__dict__[self.key + "_inst"]
+        except KeyError:
+            inst = None
+
+        # avoid exception context
+        if inst is None:
+            owner = self._calc_owner(class_)
+            if owner is not None:
+                inst = AssociationProxyInstance.for_proxy(self, owner, obj)
+                setattr(class_, self.key + "_inst", inst)
+            else:
+                inst = None
+
+        if inst is not None and not inst._is_canonical:
+            # the AssociationProxyInstance can't be generalized
+            # since the proxied attribute is not on the targeted
+            # class, only on subclasses of it, which might be
+            # different.  only return for the specific
+            # object's current value
+            return inst._non_canonical_get_for_object(obj)  # type: ignore
+        else:
+            return inst  # type: ignore  # TODO
+
+    def _calc_owner(self, target_cls: Any) -> Any:
+        # we might be getting invoked for a subclass
+        # that is not mapped yet, in some declarative situations.
+        # save until we are mapped
+        try:
+            insp = inspect(target_cls)
+        except exc.NoInspectionAvailable:
+            # can't find a mapper, don't set owner. if we are a not-yet-mapped
+            # subclass, we can also scan through __mro__ to find a mapped
+            # class, but instead just wait for us to be called again against a
+            # mapped class normally.
+            return None
+        else:
+            return insp.mapper.class_manager.class_
+
+    def _default_getset(
+        self, collection_class: Any
+    ) -> Tuple[_GetterProtocol[Any], _SetterProtocol]:
+        attr = self.value_attr
+        _getter = operator.attrgetter(attr)
+
+        def getter(instance: Any) -> Optional[Any]:
+            return _getter(instance) if instance is not None else None
+
+        if collection_class is dict:
+
+            def dict_setter(instance: Any, k: Any, value: Any) -> None:
+                setattr(instance, attr, value)
+
+            return getter, dict_setter
+
+        else:
+
+            def plain_setter(o: Any, v: Any) -> None:
+                setattr(o, attr, v)
+
+            return getter, plain_setter
+
+    def __repr__(self) -> str:
+        return "AssociationProxy(%r, %r)" % (
+            self.target_collection,
+            self.value_attr,
+        )
+
+
+# the pep-673 Self type does not work in Mypy for a "hybrid"
+# style method that returns type or Self, so for one specific case
+# we still need to use the pre-pep-673 workaround.
+_Self = TypeVar("_Self", bound="AssociationProxyInstance[Any]")
+
+
+class AssociationProxyInstance(SQLORMOperations[_T]):
+    """A per-class object that serves class- and object-specific results.
+
+    This is used by :class:`.AssociationProxy` when it is invoked
+    in terms of a specific class or instance of a class, i.e. when it is
+    used as a regular Python descriptor.
+
+    When referring to the :class:`.AssociationProxy` as a normal Python
+    descriptor, the :class:`.AssociationProxyInstance` is the object that
+    actually serves the information.   Under normal circumstances, its presence
+    is transparent::
+
+        >>> User.keywords.scalar
+        False
+
+    In the special case that the :class:`.AssociationProxy` object is being
+    accessed directly, in order to get an explicit handle to the
+    :class:`.AssociationProxyInstance`, use the
+    :meth:`.AssociationProxy.for_class` method::
+
+        proxy_state = inspect(User).all_orm_descriptors["keywords"].for_class(User)
+
+        # view if proxy object is scalar or not
+        >>> proxy_state.scalar
+        False
+
+    .. versionadded:: 1.3
+
+    """  # noqa
+
+    collection_class: Optional[Type[Any]]
+    parent: _AssociationProxyProtocol[_T]
+
+    def __init__(
+        self,
+        parent: _AssociationProxyProtocol[_T],
+        owning_class: Type[Any],
+        target_class: Type[Any],
+        value_attr: str,
+    ):
+        self.parent = parent
+        self.key = parent.key
+        self.owning_class = owning_class
+        self.target_collection = parent.target_collection
+        self.collection_class = None
+        self.target_class = target_class
+        self.value_attr = value_attr
+
+    target_class: Type[Any]
+    """The intermediary class handled by this
+    :class:`.AssociationProxyInstance`.
+
+    Intercepted append/set/assignment events will result
+    in the generation of new instances of this class.
+
+    """
+
+    @classmethod
+    def for_proxy(
+        cls,
+        parent: AssociationProxy[_T],
+        owning_class: Type[Any],
+        parent_instance: Any,
+    ) -> AssociationProxyInstance[_T]:
+        target_collection = parent.target_collection
+        value_attr = parent.value_attr
+        prop = cast(
+            "orm.RelationshipProperty[_T]",
+            orm.class_mapper(owning_class).get_property(target_collection),
+        )
+
+        # this was never asserted before but this should be made clear.
+        if not isinstance(prop, orm.RelationshipProperty):
+            raise NotImplementedError(
+                "association proxy to a non-relationship "
+                "intermediary is not supported"
+            ) from None
+
+        target_class = prop.mapper.class_
+
+        try:
+            target_assoc = cast(
+                "AssociationProxyInstance[_T]",
+                cls._cls_unwrap_target_assoc_proxy(target_class, value_attr),
+            )
+        except AttributeError:
+            # the proxied attribute doesn't exist on the target class;
+            # return an "ambiguous" instance that will work on a per-object
+            # basis
+            return AmbiguousAssociationProxyInstance(
+                parent, owning_class, target_class, value_attr
+            )
+        except Exception as err:
+            raise exc.InvalidRequestError(
+                f"Association proxy received an unexpected error when "
+                f"trying to retreive attribute "
+                f'"{target_class.__name__}.{parent.value_attr}" from '
+                f'class "{target_class.__name__}": {err}'
+            ) from err
+        else:
+            return cls._construct_for_assoc(
+                target_assoc, parent, owning_class, target_class, value_attr
+            )
+
+    @classmethod
+    def _construct_for_assoc(
+        cls,
+        target_assoc: Optional[AssociationProxyInstance[_T]],
+        parent: _AssociationProxyProtocol[_T],
+        owning_class: Type[Any],
+        target_class: Type[Any],
+        value_attr: str,
+    ) -> AssociationProxyInstance[_T]:
+        if target_assoc is not None:
+            return ObjectAssociationProxyInstance(
+                parent, owning_class, target_class, value_attr
+            )
+
+        attr = getattr(target_class, value_attr)
+        if not hasattr(attr, "_is_internal_proxy"):
+            return AmbiguousAssociationProxyInstance(
+                parent, owning_class, target_class, value_attr
+            )
+        is_object = attr._impl_uses_objects
+        if is_object:
+            return ObjectAssociationProxyInstance(
+                parent, owning_class, target_class, value_attr
+            )
+        else:
+            return ColumnAssociationProxyInstance(
+                parent, owning_class, target_class, value_attr
+            )
+
+    def _get_property(self) -> MapperProperty[Any]:
+        return orm.class_mapper(self.owning_class).get_property(
+            self.target_collection
+        )
+
+    @property
+    def _comparator(self) -> PropComparator[Any]:
+        return getattr(  # type: ignore
+            self.owning_class, self.target_collection
+        ).comparator
+
+    def __clause_element__(self) -> NoReturn:
+        raise NotImplementedError(
+            "The association proxy can't be used as a plain column "
+            "expression; it only works inside of a comparison expression"
+        )
+
+    @classmethod
+    def _cls_unwrap_target_assoc_proxy(
+        cls, target_class: Any, value_attr: str
+    ) -> Optional[AssociationProxyInstance[_T]]:
+        attr = getattr(target_class, value_attr)
+        assert not isinstance(attr, AssociationProxy)
+        if isinstance(attr, AssociationProxyInstance):
+            return attr
+        return None
+
+    @util.memoized_property
+    def _unwrap_target_assoc_proxy(
+        self,
+    ) -> Optional[AssociationProxyInstance[_T]]:
+        return self._cls_unwrap_target_assoc_proxy(
+            self.target_class, self.value_attr
+        )
+
+    @property
+    def remote_attr(self) -> SQLORMOperations[_T]:
+        """The 'remote' class attribute referenced by this
+        :class:`.AssociationProxyInstance`.
+
+        .. seealso::
+
+            :attr:`.AssociationProxyInstance.attr`
+
+            :attr:`.AssociationProxyInstance.local_attr`
+
+        """
+        return cast(
+            "SQLORMOperations[_T]", getattr(self.target_class, self.value_attr)
+        )
+
+    @property
+    def local_attr(self) -> SQLORMOperations[Any]:
+        """The 'local' class attribute referenced by this
+        :class:`.AssociationProxyInstance`.
+
+        .. seealso::
+
+            :attr:`.AssociationProxyInstance.attr`
+
+            :attr:`.AssociationProxyInstance.remote_attr`
+
+        """
+        return cast(
+            "SQLORMOperations[Any]",
+            getattr(self.owning_class, self.target_collection),
+        )
+
+    @property
+    def attr(self) -> Tuple[SQLORMOperations[Any], SQLORMOperations[_T]]:
+        """Return a tuple of ``(local_attr, remote_attr)``.
+
+        This attribute was originally intended to facilitate using the
+        :meth:`_query.Query.join` method to join across the two relationships
+        at once, however this makes use of a deprecated calling style.
+
+        To use :meth:`_sql.select.join` or :meth:`_orm.Query.join` with
+        an association proxy, the current method is to make use of the
+        :attr:`.AssociationProxyInstance.local_attr` and
+        :attr:`.AssociationProxyInstance.remote_attr` attributes separately::
+
+            stmt = (
+                select(Parent).
+                join(Parent.proxied.local_attr).
+                join(Parent.proxied.remote_attr)
+            )
+
+        A future release may seek to provide a more succinct join pattern
+        for association proxy attributes.
+
+        .. seealso::
+
+            :attr:`.AssociationProxyInstance.local_attr`
+
+            :attr:`.AssociationProxyInstance.remote_attr`
+
+        """
+        return (self.local_attr, self.remote_attr)
+
+    @util.memoized_property
+    def scalar(self) -> bool:
+        """Return ``True`` if this :class:`.AssociationProxyInstance`
+        proxies a scalar relationship on the local side."""
+
+        scalar = not self._get_property().uselist
+        if scalar:
+            self._initialize_scalar_accessors()
+        return scalar
+
+    @util.memoized_property
+    def _value_is_scalar(self) -> bool:
+        return (
+            not self._get_property()
+            .mapper.get_property(self.value_attr)
+            .uselist
+        )
+
+    @property
+    def _target_is_object(self) -> bool:
+        raise NotImplementedError()
+
+    _scalar_get: _GetterProtocol[_T]
+    _scalar_set: _PlainSetterProtocol[_T]
+
+    def _initialize_scalar_accessors(self) -> None:
+        if self.parent.getset_factory:
+            get, set_ = self.parent.getset_factory(None, self)
+        else:
+            get, set_ = self.parent._default_getset(None)
+        self._scalar_get, self._scalar_set = get, cast(
+            "_PlainSetterProtocol[_T]", set_
+        )
+
+    def _default_getset(
+        self, collection_class: Any
+    ) -> Tuple[_GetterProtocol[Any], _SetterProtocol]:
+        attr = self.value_attr
+        _getter = operator.attrgetter(attr)
+
+        def getter(instance: Any) -> Optional[_T]:
+            return _getter(instance) if instance is not None else None
+
+        if collection_class is dict:
+
+            def dict_setter(instance: Any, k: Any, value: _T) -> None:
+                setattr(instance, attr, value)
+
+            return getter, dict_setter
+        else:
+
+            def plain_setter(o: Any, v: _T) -> None:
+                setattr(o, attr, v)
+
+            return getter, plain_setter
+
+    @util.ro_non_memoized_property
+    def info(self) -> _InfoType:
+        return self.parent.info
+
+    @overload
+    def get(self: _Self, obj: Literal[None]) -> _Self: ...
+
+    @overload
+    def get(self, obj: Any) -> _T: ...
+
+    def get(
+        self, obj: Any
+    ) -> Union[Optional[_T], AssociationProxyInstance[_T]]:
+        if obj is None:
+            return self
+
+        proxy: _T
+
+        if self.scalar:
+            target = getattr(obj, self.target_collection)
+            return self._scalar_get(target)
+        else:
+            try:
+                # If the owning instance is reborn (orm session resurrect,
+                # etc.), refresh the proxy cache.
+                creator_id, self_id, proxy = cast(
+                    "Tuple[int, int, _T]", getattr(obj, self.key)
+                )
+            except AttributeError:
+                pass
+            else:
+                if id(obj) == creator_id and id(self) == self_id:
+                    assert self.collection_class is not None
+                    return proxy
+
+            self.collection_class, proxy = self._new(
+                _lazy_collection(obj, self.target_collection)
+            )
+            setattr(obj, self.key, (id(obj), id(self), proxy))
+            return proxy
+
+    def set(self, obj: Any, values: _T) -> None:
+        if self.scalar:
+            creator = cast(
+                "_PlainCreatorProtocol[_T]",
+                (
+                    self.parent.creator
+                    if self.parent.creator
+                    else self.target_class
+                ),
+            )
+            target = getattr(obj, self.target_collection)
+            if target is None:
+                if (
+                    values is None
+                    and not self.parent.create_on_none_assignment
+                ):
+                    return
+                setattr(obj, self.target_collection, creator(values))
+            else:
+                self._scalar_set(target, values)
+                if values is None and self.parent.cascade_scalar_deletes:
+                    setattr(obj, self.target_collection, None)
+        else:
+            proxy = self.get(obj)
+            assert self.collection_class is not None
+            if proxy is not values:
+                proxy._bulk_replace(self, values)
+
+    def delete(self, obj: Any) -> None:
+        if self.owning_class is None:
+            self._calc_owner(obj, None)
+
+        if self.scalar:
+            target = getattr(obj, self.target_collection)
+            if target is not None:
+                delattr(target, self.value_attr)
+        delattr(obj, self.target_collection)
+
+    def _new(
+        self, lazy_collection: _LazyCollectionProtocol[_T]
+    ) -> Tuple[Type[Any], _T]:
+        creator = (
+            self.parent.creator
+            if self.parent.creator is not None
+            else cast("_CreatorProtocol", self.target_class)
+        )
+        collection_class = util.duck_type_collection(lazy_collection())
+
+        if collection_class is None:
+            raise exc.InvalidRequestError(
+                f"lazy collection factory did not return a "
+                f"valid collection type, got {collection_class}"
+            )
+        if self.parent.proxy_factory:
+            return (
+                collection_class,
+                self.parent.proxy_factory(
+                    lazy_collection, creator, self.value_attr, self
+                ),
+            )
+
+        if self.parent.getset_factory:
+            getter, setter = self.parent.getset_factory(collection_class, self)
+        else:
+            getter, setter = self.parent._default_getset(collection_class)
+
+        if collection_class is list:
+            return (
+                collection_class,
+                cast(
+                    _T,
+                    _AssociationList(
+                        lazy_collection, creator, getter, setter, self
+                    ),
+                ),
+            )
+        elif collection_class is dict:
+            return (
+                collection_class,
+                cast(
+                    _T,
+                    _AssociationDict(
+                        lazy_collection, creator, getter, setter, self
+                    ),
+                ),
+            )
+        elif collection_class is set:
+            return (
+                collection_class,
+                cast(
+                    _T,
+                    _AssociationSet(
+                        lazy_collection, creator, getter, setter, self
+                    ),
+                ),
+            )
+        else:
+            raise exc.ArgumentError(
+                "could not guess which interface to use for "
+                'collection_class "%s" backing "%s"; specify a '
+                "proxy_factory and proxy_bulk_set manually"
+                % (self.collection_class, self.target_collection)
+            )
+
+    def _set(
+        self, proxy: _AssociationCollection[Any], values: Iterable[Any]
+    ) -> None:
+        if self.parent.proxy_bulk_set:
+            self.parent.proxy_bulk_set(proxy, values)
+        elif self.collection_class is list:
+            cast("_AssociationList[Any]", proxy).extend(values)
+        elif self.collection_class is dict:
+            cast("_AssociationDict[Any, Any]", proxy).update(values)
+        elif self.collection_class is set:
+            cast("_AssociationSet[Any]", proxy).update(values)
+        else:
+            raise exc.ArgumentError(
+                "no proxy_bulk_set supplied for custom "
+                "collection_class implementation"
+            )
+
+    def _inflate(self, proxy: _AssociationCollection[Any]) -> None:
+        creator = (
+            self.parent.creator
+            and self.parent.creator
+            or cast(_CreatorProtocol, self.target_class)
+        )
+
+        if self.parent.getset_factory:
+            getter, setter = self.parent.getset_factory(
+                self.collection_class, self
+            )
+        else:
+            getter, setter = self.parent._default_getset(self.collection_class)
+
+        proxy.creator = creator
+        proxy.getter = getter
+        proxy.setter = setter
+
+    def _criterion_exists(
+        self,
+        criterion: Optional[_ColumnExpressionArgument[bool]] = None,
+        **kwargs: Any,
+    ) -> ColumnElement[bool]:
+        is_has = kwargs.pop("is_has", None)
+
+        target_assoc = self._unwrap_target_assoc_proxy
+        if target_assoc is not None:
+            inner = target_assoc._criterion_exists(
+                criterion=criterion, **kwargs
+            )
+            return self._comparator._criterion_exists(inner)
+
+        if self._target_is_object:
+            attr = getattr(self.target_class, self.value_attr)
+            value_expr = attr.comparator._criterion_exists(criterion, **kwargs)
+        else:
+            if kwargs:
+                raise exc.ArgumentError(
+                    "Can't apply keyword arguments to column-targeted "
+                    "association proxy; use =="
+                )
+            elif is_has and criterion is not None:
+                raise exc.ArgumentError(
+                    "Non-empty has() not allowed for "
+                    "column-targeted association proxy; use =="
+                )
+
+            value_expr = criterion
+
+        return self._comparator._criterion_exists(value_expr)
+
+    def any(
+        self,
+        criterion: Optional[_ColumnExpressionArgument[bool]] = None,
+        **kwargs: Any,
+    ) -> ColumnElement[bool]:
+        """Produce a proxied 'any' expression using EXISTS.
+
+        This expression will be a composed product
+        using the :meth:`.Relationship.Comparator.any`
+        and/or :meth:`.Relationship.Comparator.has`
+        operators of the underlying proxied attributes.
+
+        """
+        if self._unwrap_target_assoc_proxy is None and (
+            self.scalar
+            and (not self._target_is_object or self._value_is_scalar)
+        ):
+            raise exc.InvalidRequestError(
+                "'any()' not implemented for scalar attributes. Use has()."
+            )
+        return self._criterion_exists(
+            criterion=criterion, is_has=False, **kwargs
+        )
+
+    def has(
+        self,
+        criterion: Optional[_ColumnExpressionArgument[bool]] = None,
+        **kwargs: Any,
+    ) -> ColumnElement[bool]:
+        """Produce a proxied 'has' expression using EXISTS.
+
+        This expression will be a composed product
+        using the :meth:`.Relationship.Comparator.any`
+        and/or :meth:`.Relationship.Comparator.has`
+        operators of the underlying proxied attributes.
+
+        """
+        if self._unwrap_target_assoc_proxy is None and (
+            not self.scalar
+            or (self._target_is_object and not self._value_is_scalar)
+        ):
+            raise exc.InvalidRequestError(
+                "'has()' not implemented for collections. Use any()."
+            )
+        return self._criterion_exists(
+            criterion=criterion, is_has=True, **kwargs
+        )
+
+    def __repr__(self) -> str:
+        return "%s(%r)" % (self.__class__.__name__, self.parent)
+
+
+class AmbiguousAssociationProxyInstance(AssociationProxyInstance[_T]):
+    """an :class:`.AssociationProxyInstance` where we cannot determine
+    the type of target object.
+    """
+
+    _is_canonical = False
+
+    def _ambiguous(self) -> NoReturn:
+        raise AttributeError(
+            "Association proxy %s.%s refers to an attribute '%s' that is not "
+            "directly mapped on class %s; therefore this operation cannot "
+            "proceed since we don't know what type of object is referred "
+            "towards"
+            % (
+                self.owning_class.__name__,
+                self.target_collection,
+                self.value_attr,
+                self.target_class,
+            )
+        )
+
+    def get(self, obj: Any) -> Any:
+        if obj is None:
+            return self
+        else:
+            return super().get(obj)
+
+    def __eq__(self, obj: object) -> NoReturn:
+        self._ambiguous()
+
+    def __ne__(self, obj: object) -> NoReturn:
+        self._ambiguous()
+
+    def any(
+        self,
+        criterion: Optional[_ColumnExpressionArgument[bool]] = None,
+        **kwargs: Any,
+    ) -> NoReturn:
+        self._ambiguous()
+
+    def has(
+        self,
+        criterion: Optional[_ColumnExpressionArgument[bool]] = None,
+        **kwargs: Any,
+    ) -> NoReturn:
+        self._ambiguous()
+
+    @util.memoized_property
+    def _lookup_cache(self) -> Dict[Type[Any], AssociationProxyInstance[_T]]:
+        # mapping of <subclass>->AssociationProxyInstance.
+        # e.g. proxy is A-> A.b -> B -> B.b_attr, but B.b_attr doesn't exist;
+        # only B1(B) and B2(B) have "b_attr", keys in here would be B1, B2
+        return {}
+
+    def _non_canonical_get_for_object(
+        self, parent_instance: Any
+    ) -> AssociationProxyInstance[_T]:
+        if parent_instance is not None:
+            actual_obj = getattr(parent_instance, self.target_collection)
+            if actual_obj is not None:
+                try:
+                    insp = inspect(actual_obj)
+                except exc.NoInspectionAvailable:
+                    pass
+                else:
+                    mapper = insp.mapper
+                    instance_class = mapper.class_
+                    if instance_class not in self._lookup_cache:
+                        self._populate_cache(instance_class, mapper)
+
+                    try:
+                        return self._lookup_cache[instance_class]
+                    except KeyError:
+                        pass
+
+        # no object or ambiguous object given, so return "self", which
+        # is a proxy with generally only instance-level functionality
+        return self
+
+    def _populate_cache(
+        self, instance_class: Any, mapper: Mapper[Any]
+    ) -> None:
+        prop = orm.class_mapper(self.owning_class).get_property(
+            self.target_collection
+        )
+
+        if mapper.isa(prop.mapper):
+            target_class = instance_class
+            try:
+                target_assoc = self._cls_unwrap_target_assoc_proxy(
+                    target_class, self.value_attr
+                )
+            except AttributeError:
+                pass
+            else:
+                self._lookup_cache[instance_class] = self._construct_for_assoc(
+                    cast("AssociationProxyInstance[_T]", target_assoc),
+                    self.parent,
+                    self.owning_class,
+                    target_class,
+                    self.value_attr,
+                )
+
+
+class ObjectAssociationProxyInstance(AssociationProxyInstance[_T]):
+    """an :class:`.AssociationProxyInstance` that has an object as a target."""
+
+    _target_is_object: bool = True
+    _is_canonical = True
+
+    def contains(self, other: Any, **kw: Any) -> ColumnElement[bool]:
+        """Produce a proxied 'contains' expression using EXISTS.
+
+        This expression will be a composed product
+        using the :meth:`.Relationship.Comparator.any`,
+        :meth:`.Relationship.Comparator.has`,
+        and/or :meth:`.Relationship.Comparator.contains`
+        operators of the underlying proxied attributes.
+        """
+
+        target_assoc = self._unwrap_target_assoc_proxy
+        if target_assoc is not None:
+            return self._comparator._criterion_exists(
+                target_assoc.contains(other)
+                if not target_assoc.scalar
+                else target_assoc == other
+            )
+        elif (
+            self._target_is_object
+            and self.scalar
+            and not self._value_is_scalar
+        ):
+            return self._comparator.has(
+                getattr(self.target_class, self.value_attr).contains(other)
+            )
+        elif self._target_is_object and self.scalar and self._value_is_scalar:
+            raise exc.InvalidRequestError(
+                "contains() doesn't apply to a scalar object endpoint; use =="
+            )
+        else:
+            return self._comparator._criterion_exists(
+                **{self.value_attr: other}
+            )
+
+    def __eq__(self, obj: Any) -> ColumnElement[bool]:  # type: ignore[override]  # noqa: E501
+        # note the has() here will fail for collections; eq_()
+        # is only allowed with a scalar.
+        if obj is None:
+            return or_(
+                self._comparator.has(**{self.value_attr: obj}),
+                self._comparator == None,
+            )
+        else:
+            return self._comparator.has(**{self.value_attr: obj})
+
+    def __ne__(self, obj: Any) -> ColumnElement[bool]:  # type: ignore[override]  # noqa: E501
+        # note the has() here will fail for collections; eq_()
+        # is only allowed with a scalar.
+        return self._comparator.has(
+            getattr(self.target_class, self.value_attr) != obj
+        )
+
+
+class ColumnAssociationProxyInstance(AssociationProxyInstance[_T]):
+    """an :class:`.AssociationProxyInstance` that has a database column as a
+    target.
+    """
+
+    _target_is_object: bool = False
+    _is_canonical = True
+
+    def __eq__(self, other: Any) -> ColumnElement[bool]:  # type: ignore[override]  # noqa: E501
+        # special case "is None" to check for no related row as well
+        expr = self._criterion_exists(
+            self.remote_attr.operate(operators.eq, other)
+        )
+        if other is None:
+            return or_(expr, self._comparator == None)
+        else:
+            return expr
+
+    def operate(
+        self, op: operators.OperatorType, *other: Any, **kwargs: Any
+    ) -> ColumnElement[Any]:
+        return self._criterion_exists(
+            self.remote_attr.operate(op, *other, **kwargs)
+        )
+
+
+class _lazy_collection(_LazyCollectionProtocol[_T]):
+    def __init__(self, obj: Any, target: str):
+        self.parent = obj
+        self.target = target
+
+    def __call__(
+        self,
+    ) -> Union[MutableSet[_T], MutableMapping[Any, _T], MutableSequence[_T]]:
+        return getattr(self.parent, self.target)  # type: ignore[no-any-return]
+
+    def __getstate__(self) -> Any:
+        return {"obj": self.parent, "target": self.target}
+
+    def __setstate__(self, state: Any) -> None:
+        self.parent = state["obj"]
+        self.target = state["target"]
+
+
+_IT = TypeVar("_IT", bound="Any")
+"""instance type - this is the type of object inside a collection.
+
+this is not the same as the _T of AssociationProxy and
+AssociationProxyInstance itself, which will often refer to the
+collection[_IT] type.
+
+"""
+
+
+class _AssociationCollection(Generic[_IT]):
+    getter: _GetterProtocol[_IT]
+    """A function.  Given an associated object, return the 'value'."""
+
+    creator: _CreatorProtocol
+    """
+    A function that creates new target entities.  Given one parameter:
+    value.  This assertion is assumed::
+
+    obj = creator(somevalue)
+    assert getter(obj) == somevalue
+    """
+
+    parent: AssociationProxyInstance[_IT]
+    setter: _SetterProtocol
+    """A function.  Given an associated object and a value, store that
+        value on the object.
+    """
+
+    lazy_collection: _LazyCollectionProtocol[_IT]
+    """A callable returning a list-based collection of entities (usually an
+          object attribute managed by a SQLAlchemy relationship())"""
+
+    def __init__(
+        self,
+        lazy_collection: _LazyCollectionProtocol[_IT],
+        creator: _CreatorProtocol,
+        getter: _GetterProtocol[_IT],
+        setter: _SetterProtocol,
+        parent: AssociationProxyInstance[_IT],
+    ):
+        """Constructs an _AssociationCollection.
+
+        This will always be a subclass of either _AssociationList,
+        _AssociationSet, or _AssociationDict.
+
+        """
+        self.lazy_collection = lazy_collection
+        self.creator = creator
+        self.getter = getter
+        self.setter = setter
+        self.parent = parent
+
+    if typing.TYPE_CHECKING:
+        col: Collection[_IT]
+    else:
+        col = property(lambda self: self.lazy_collection())
+
+    def __len__(self) -> int:
+        return len(self.col)
+
+    def __bool__(self) -> bool:
+        return bool(self.col)
+
+    def __getstate__(self) -> Any:
+        return {"parent": self.parent, "lazy_collection": self.lazy_collection}
+
+    def __setstate__(self, state: Any) -> None:
+        self.parent = state["parent"]
+        self.lazy_collection = state["lazy_collection"]
+        self.parent._inflate(self)
+
+    def clear(self) -> None:
+        raise NotImplementedError()
+
+
+class _AssociationSingleItem(_AssociationCollection[_T]):
+    setter: _PlainSetterProtocol[_T]
+    creator: _PlainCreatorProtocol[_T]
+
+    def _create(self, value: _T) -> Any:
+        return self.creator(value)
+
+    def _get(self, object_: Any) -> _T:
+        return self.getter(object_)
+
+    def _bulk_replace(
+        self, assoc_proxy: AssociationProxyInstance[Any], values: Iterable[_IT]
+    ) -> None:
+        self.clear()
+        assoc_proxy._set(self, values)
+
+
+class _AssociationList(_AssociationSingleItem[_T], MutableSequence[_T]):
+    """Generic, converting, list-to-list proxy."""
+
+    col: MutableSequence[_T]
+
+    def _set(self, object_: Any, value: _T) -> None:
+        self.setter(object_, value)
+
+    @overload
+    def __getitem__(self, index: int) -> _T: ...
+
+    @overload
+    def __getitem__(self, index: slice) -> MutableSequence[_T]: ...
+
+    def __getitem__(
+        self, index: Union[int, slice]
+    ) -> Union[_T, MutableSequence[_T]]:
+        if not isinstance(index, slice):
+            return self._get(self.col[index])
+        else:
+            return [self._get(member) for member in self.col[index]]
+
+    @overload
+    def __setitem__(self, index: int, value: _T) -> None: ...
+
+    @overload
+    def __setitem__(self, index: slice, value: Iterable[_T]) -> None: ...
+
+    def __setitem__(
+        self, index: Union[int, slice], value: Union[_T, Iterable[_T]]
+    ) -> None:
+        if not isinstance(index, slice):
+            self._set(self.col[index], cast("_T", value))
+        else:
+            if index.stop is None:
+                stop = len(self)
+            elif index.stop < 0:
+                stop = len(self) + index.stop
+            else:
+                stop = index.stop
+            step = index.step or 1
+
+            start = index.start or 0
+            rng = list(range(index.start or 0, stop, step))
+
+            sized_value = list(value)
+
+            if step == 1:
+                for i in rng:
+                    del self[start]
+                i = start
+                for item in sized_value:
+                    self.insert(i, item)
+                    i += 1
+            else:
+                if len(sized_value) != len(rng):
+                    raise ValueError(
+                        "attempt to assign sequence of size %s to "
+                        "extended slice of size %s"
+                        % (len(sized_value), len(rng))
+                    )
+                for i, item in zip(rng, value):
+                    self._set(self.col[i], item)
+
+    @overload
+    def __delitem__(self, index: int) -> None: ...
+
+    @overload
+    def __delitem__(self, index: slice) -> None: ...
+
+    def __delitem__(self, index: Union[slice, int]) -> None:
+        del self.col[index]
+
+    def __contains__(self, value: object) -> bool:
+        for member in self.col:
+            # testlib.pragma exempt:__eq__
+            if self._get(member) == value:
+                return True
+        return False
+
+    def __iter__(self) -> Iterator[_T]:
+        """Iterate over proxied values.
+
+        For the actual domain objects, iterate over .col instead or
+        just use the underlying collection directly from its property
+        on the parent.
+        """
+
+        for member in self.col:
+            yield self._get(member)
+        return
+
+    def append(self, value: _T) -> None:
+        col = self.col
+        item = self._create(value)
+        col.append(item)
+
+    def count(self, value: Any) -> int:
+        count = 0
+        for v in self:
+            if v == value:
+                count += 1
+        return count
+
+    def extend(self, values: Iterable[_T]) -> None:
+        for v in values:
+            self.append(v)
+
+    def insert(self, index: int, value: _T) -> None:
+        self.col[index:index] = [self._create(value)]
+
+    def pop(self, index: int = -1) -> _T:
+        return self.getter(self.col.pop(index))
+
+    def remove(self, value: _T) -> None:
+        for i, val in enumerate(self):
+            if val == value:
+                del self.col[i]
+                return
+        raise ValueError("value not in list")
+
+    def reverse(self) -> NoReturn:
+        """Not supported, use reversed(mylist)"""
+
+        raise NotImplementedError()
+
+    def sort(self) -> NoReturn:
+        """Not supported, use sorted(mylist)"""
+
+        raise NotImplementedError()
+
+    def clear(self) -> None:
+        del self.col[0 : len(self.col)]
+
+    def __eq__(self, other: object) -> bool:
+        return list(self) == other
+
+    def __ne__(self, other: object) -> bool:
+        return list(self) != other
+
+    def __lt__(self, other: List[_T]) -> bool:
+        return list(self) < other
+
+    def __le__(self, other: List[_T]) -> bool:
+        return list(self) <= other
+
+    def __gt__(self, other: List[_T]) -> bool:
+        return list(self) > other
+
+    def __ge__(self, other: List[_T]) -> bool:
+        return list(self) >= other
+
+    def __add__(self, other: List[_T]) -> List[_T]:
+        try:
+            other = list(other)
+        except TypeError:
+            return NotImplemented
+        return list(self) + other
+
+    def __radd__(self, other: List[_T]) -> List[_T]:
+        try:
+            other = list(other)
+        except TypeError:
+            return NotImplemented
+        return other + list(self)
+
+    def __mul__(self, n: SupportsIndex) -> List[_T]:
+        if not isinstance(n, int):
+            return NotImplemented
+        return list(self) * n
+
+    def __rmul__(self, n: SupportsIndex) -> List[_T]:
+        if not isinstance(n, int):
+            return NotImplemented
+        return n * list(self)
+
+    def __iadd__(self, iterable: Iterable[_T]) -> Self:
+        self.extend(iterable)
+        return self
+
+    def __imul__(self, n: SupportsIndex) -> Self:
+        # unlike a regular list *=, proxied __imul__ will generate unique
+        # backing objects for each copy.  *= on proxied lists is a bit of
+        # a stretch anyhow, and this interpretation of the __imul__ contract
+        # is more plausibly useful than copying the backing objects.
+        if not isinstance(n, int):
+            raise NotImplementedError()
+        if n == 0:
+            self.clear()
+        elif n > 1:
+            self.extend(list(self) * (n - 1))
+        return self
+
+    if typing.TYPE_CHECKING:
+        # TODO: no idea how to do this without separate "stub"
+        def index(
+            self, value: Any, start: int = ..., stop: int = ...
+        ) -> int: ...
+
+    else:
+
+        def index(self, value: Any, *arg) -> int:
+            ls = list(self)
+            return ls.index(value, *arg)
+
+    def copy(self) -> List[_T]:
+        return list(self)
+
+    def __repr__(self) -> str:
+        return repr(list(self))
+
+    def __hash__(self) -> NoReturn:
+        raise TypeError("%s objects are unhashable" % type(self).__name__)
+
+    if not typing.TYPE_CHECKING:
+        for func_name, func in list(locals().items()):
+            if (
+                callable(func)
+                and func.__name__ == func_name
+                and not func.__doc__
+                and hasattr(list, func_name)
+            ):
+                func.__doc__ = getattr(list, func_name).__doc__
+        del func_name, func
+
+
+class _AssociationDict(_AssociationCollection[_VT], MutableMapping[_KT, _VT]):
+    """Generic, converting, dict-to-dict proxy."""
+
+    setter: _DictSetterProtocol[_VT]
+    creator: _KeyCreatorProtocol[_VT]
+    col: MutableMapping[_KT, Optional[_VT]]
+
+    def _create(self, key: _KT, value: Optional[_VT]) -> Any:
+        return self.creator(key, value)
+
+    def _get(self, object_: Any) -> _VT:
+        return self.getter(object_)
+
+    def _set(self, object_: Any, key: _KT, value: _VT) -> None:
+        return self.setter(object_, key, value)
+
+    def __getitem__(self, key: _KT) -> _VT:
+        return self._get(self.col[key])
+
+    def __setitem__(self, key: _KT, value: _VT) -> None:
+        if key in self.col:
+            self._set(self.col[key], key, value)
+        else:
+            self.col[key] = self._create(key, value)
+
+    def __delitem__(self, key: _KT) -> None:
+        del self.col[key]
+
+    def __contains__(self, key: object) -> bool:
+        return key in self.col
+
+    def __iter__(self) -> Iterator[_KT]:
+        return iter(self.col.keys())
+
+    def clear(self) -> None:
+        self.col.clear()
+
+    def __eq__(self, other: object) -> bool:
+        return dict(self) == other
+
+    def __ne__(self, other: object) -> bool:
+        return dict(self) != other
+
+    def __repr__(self) -> str:
+        return repr(dict(self))
+
+    @overload
+    def get(self, __key: _KT) -> Optional[_VT]: ...
+
+    @overload
+    def get(self, __key: _KT, default: Union[_VT, _T]) -> Union[_VT, _T]: ...
+
+    def get(
+        self, key: _KT, default: Optional[Union[_VT, _T]] = None
+    ) -> Union[_VT, _T, None]:
+        try:
+            return self[key]
+        except KeyError:
+            return default
+
+    def setdefault(self, key: _KT, default: Optional[_VT] = None) -> _VT:
+        # TODO: again, no idea how to create an actual MutableMapping.
+        # default must allow None, return type can't include None,
+        # the stub explicitly allows for default of None with a cryptic message
+        # "This overload should be allowed only if the value type is
+        # compatible with None.".
+        if key not in self.col:
+            self.col[key] = self._create(key, default)
+            return default  # type: ignore
+        else:
+            return self[key]
+
+    def keys(self) -> KeysView[_KT]:
+        return self.col.keys()
+
+    def items(self) -> ItemsView[_KT, _VT]:
+        return ItemsView(self)
+
+    def values(self) -> ValuesView[_VT]:
+        return ValuesView(self)
+
+    @overload
+    def pop(self, __key: _KT) -> _VT: ...
+
+    @overload
+    def pop(
+        self, __key: _KT, default: Union[_VT, _T] = ...
+    ) -> Union[_VT, _T]: ...
+
+    def pop(self, __key: _KT, *arg: Any, **kw: Any) -> Union[_VT, _T]:
+        member = self.col.pop(__key, *arg, **kw)
+        return self._get(member)
+
+    def popitem(self) -> Tuple[_KT, _VT]:
+        item = self.col.popitem()
+        return (item[0], self._get(item[1]))
+
+    @overload
+    def update(
+        self, __m: SupportsKeysAndGetItem[_KT, _VT], **kwargs: _VT
+    ) -> None: ...
+
+    @overload
+    def update(
+        self, __m: Iterable[tuple[_KT, _VT]], **kwargs: _VT
+    ) -> None: ...
+
+    @overload
+    def update(self, **kwargs: _VT) -> None: ...
+
+    def update(self, *a: Any, **kw: Any) -> None:
+        up: Dict[_KT, _VT] = {}
+        up.update(*a, **kw)
+
+        for key, value in up.items():
+            self[key] = value
+
+    def _bulk_replace(
+        self,
+        assoc_proxy: AssociationProxyInstance[Any],
+        values: Mapping[_KT, _VT],
+    ) -> None:
+        existing = set(self)
+        constants = existing.intersection(values or ())
+        additions = set(values or ()).difference(constants)
+        removals = existing.difference(constants)
+
+        for key, member in values.items() or ():
+            if key in additions:
+                self[key] = member
+            elif key in constants:
+                self[key] = member
+
+        for key in removals:
+            del self[key]
+
+    def copy(self) -> Dict[_KT, _VT]:
+        return dict(self.items())
+
+    def __hash__(self) -> NoReturn:
+        raise TypeError("%s objects are unhashable" % type(self).__name__)
+
+    if not typing.TYPE_CHECKING:
+        for func_name, func in list(locals().items()):
+            if (
+                callable(func)
+                and func.__name__ == func_name
+                and not func.__doc__
+                and hasattr(dict, func_name)
+            ):
+                func.__doc__ = getattr(dict, func_name).__doc__
+        del func_name, func
+
+
+class _AssociationSet(_AssociationSingleItem[_T], MutableSet[_T]):
+    """Generic, converting, set-to-set proxy."""
+
+    col: MutableSet[_T]
+
+    def __len__(self) -> int:
+        return len(self.col)
+
+    def __bool__(self) -> bool:
+        if self.col:
+            return True
+        else:
+            return False
+
+    def __contains__(self, __o: object) -> bool:
+        for member in self.col:
+            if self._get(member) == __o:
+                return True
+        return False
+
+    def __iter__(self) -> Iterator[_T]:
+        """Iterate over proxied values.
+
+        For the actual domain objects, iterate over .col instead or just use
+        the underlying collection directly from its property on the parent.
+
+        """
+        for member in self.col:
+            yield self._get(member)
+        return
+
+    def add(self, __element: _T) -> None:
+        if __element not in self:
+            self.col.add(self._create(__element))
+
+    # for discard and remove, choosing a more expensive check strategy rather
+    # than call self.creator()
+    def discard(self, __element: _T) -> None:
+        for member in self.col:
+            if self._get(member) == __element:
+                self.col.discard(member)
+                break
+
+    def remove(self, __element: _T) -> None:
+        for member in self.col:
+            if self._get(member) == __element:
+                self.col.discard(member)
+                return
+        raise KeyError(__element)
+
+    def pop(self) -> _T:
+        if not self.col:
+            raise KeyError("pop from an empty set")
+        member = self.col.pop()
+        return self._get(member)
+
+    def update(self, *s: Iterable[_T]) -> None:
+        for iterable in s:
+            for value in iterable:
+                self.add(value)
+
+    def _bulk_replace(self, assoc_proxy: Any, values: Iterable[_T]) -> None:
+        existing = set(self)
+        constants = existing.intersection(values or ())
+        additions = set(values or ()).difference(constants)
+        removals = existing.difference(constants)
+
+        appender = self.add
+        remover = self.remove
+
+        for member in values or ():
+            if member in additions:
+                appender(member)
+            elif member in constants:
+                appender(member)
+
+        for member in removals:
+            remover(member)
+
+    def __ior__(  # type: ignore
+        self, other: AbstractSet[_S]
+    ) -> MutableSet[Union[_T, _S]]:
+        if not collections._set_binops_check_strict(self, other):
+            raise NotImplementedError()
+        for value in other:
+            self.add(value)
+        return self
+
+    def _set(self) -> Set[_T]:
+        return set(iter(self))
+
+    def union(self, *s: Iterable[_S]) -> MutableSet[Union[_T, _S]]:
+        return set(self).union(*s)
+
+    def __or__(self, __s: AbstractSet[_S]) -> MutableSet[Union[_T, _S]]:
+        return self.union(__s)
+
+    def difference(self, *s: Iterable[Any]) -> MutableSet[_T]:
+        return set(self).difference(*s)
+
+    def __sub__(self, s: AbstractSet[Any]) -> MutableSet[_T]:
+        return self.difference(s)
+
+    def difference_update(self, *s: Iterable[Any]) -> None:
+        for other in s:
+            for value in other:
+                self.discard(value)
+
+    def __isub__(self, s: AbstractSet[Any]) -> Self:
+        if not collections._set_binops_check_strict(self, s):
+            raise NotImplementedError()
+        for value in s:
+            self.discard(value)
+        return self
+
+    def intersection(self, *s: Iterable[Any]) -> MutableSet[_T]:
+        return set(self).intersection(*s)
+
+    def __and__(self, s: AbstractSet[Any]) -> MutableSet[_T]:
+        return self.intersection(s)
+
+    def intersection_update(self, *s: Iterable[Any]) -> None:
+        for other in s:
+            want, have = self.intersection(other), set(self)
+
+            remove, add = have - want, want - have
+
+            for value in remove:
+                self.remove(value)
+            for value in add:
+                self.add(value)
+
+    def __iand__(self, s: AbstractSet[Any]) -> Self:
+        if not collections._set_binops_check_strict(self, s):
+            raise NotImplementedError()
+        want = self.intersection(s)
+        have: Set[_T] = set(self)
+
+        remove, add = have - want, want - have
+
+        for value in remove:
+            self.remove(value)
+        for value in add:
+            self.add(value)
+        return self
+
+    def symmetric_difference(self, __s: Iterable[_T]) -> MutableSet[_T]:
+        return set(self).symmetric_difference(__s)
+
+    def __xor__(self, s: AbstractSet[_S]) -> MutableSet[Union[_T, _S]]:
+        return self.symmetric_difference(s)
+
+    def symmetric_difference_update(self, other: Iterable[Any]) -> None:
+        want, have = self.symmetric_difference(other), set(self)
+
+        remove, add = have - want, want - have
+
+        for value in remove:
+            self.remove(value)
+        for value in add:
+            self.add(value)
+
+    def __ixor__(self, other: AbstractSet[_S]) -> MutableSet[Union[_T, _S]]:  # type: ignore  # noqa: E501
+        if not collections._set_binops_check_strict(self, other):
+            raise NotImplementedError()
+
+        self.symmetric_difference_update(other)
+        return self
+
+    def issubset(self, __s: Iterable[Any]) -> bool:
+        return set(self).issubset(__s)
+
+    def issuperset(self, __s: Iterable[Any]) -> bool:
+        return set(self).issuperset(__s)
+
+    def clear(self) -> None:
+        self.col.clear()
+
+    def copy(self) -> AbstractSet[_T]:
+        return set(self)
+
+    def __eq__(self, other: object) -> bool:
+        return set(self) == other
+
+    def __ne__(self, other: object) -> bool:
+        return set(self) != other
+
+    def __lt__(self, other: AbstractSet[Any]) -> bool:
+        return set(self) < other
+
+    def __le__(self, other: AbstractSet[Any]) -> bool:
+        return set(self) <= other
+
+    def __gt__(self, other: AbstractSet[Any]) -> bool:
+        return set(self) > other
+
+    def __ge__(self, other: AbstractSet[Any]) -> bool:
+        return set(self) >= other
+
+    def __repr__(self) -> str:
+        return repr(set(self))
+
+    def __hash__(self) -> NoReturn:
+        raise TypeError("%s objects are unhashable" % type(self).__name__)
+
+    if not typing.TYPE_CHECKING:
+        for func_name, func in list(locals().items()):
+            if (
+                callable(func)
+                and func.__name__ == func_name
+                and not func.__doc__
+                and hasattr(set, func_name)
+            ):
+                func.__doc__ = getattr(set, func_name).__doc__
+        del func_name, func