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+# orm/strategy_options.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
+# mypy: allow-untyped-defs, allow-untyped-calls
+
+"""
+
+"""
+
+from __future__ import annotations
+
+import typing
+from typing import Any
+from typing import Callable
+from typing import cast
+from typing import Dict
+from typing import Iterable
+from typing import Optional
+from typing import overload
+from typing import Sequence
+from typing import Tuple
+from typing import Type
+from typing import TypeVar
+from typing import Union
+
+from . import util as orm_util
+from ._typing import insp_is_aliased_class
+from ._typing import insp_is_attribute
+from ._typing import insp_is_mapper
+from ._typing import insp_is_mapper_property
+from .attributes import QueryableAttribute
+from .base import InspectionAttr
+from .interfaces import LoaderOption
+from .path_registry import _DEFAULT_TOKEN
+from .path_registry import _StrPathToken
+from .path_registry import _WILDCARD_TOKEN
+from .path_registry import AbstractEntityRegistry
+from .path_registry import path_is_property
+from .path_registry import PathRegistry
+from .path_registry import TokenRegistry
+from .util import _orm_full_deannotate
+from .util import AliasedInsp
+from .. import exc as sa_exc
+from .. import inspect
+from .. import util
+from ..sql import and_
+from ..sql import cache_key
+from ..sql import coercions
+from ..sql import roles
+from ..sql import traversals
+from ..sql import visitors
+from ..sql.base import _generative
+from ..util.typing import Final
+from ..util.typing import Literal
+from ..util.typing import Self
+
+_RELATIONSHIP_TOKEN: Final[Literal["relationship"]] = "relationship"
+_COLUMN_TOKEN: Final[Literal["column"]] = "column"
+
+_FN = TypeVar("_FN", bound="Callable[..., Any]")
+
+if typing.TYPE_CHECKING:
+    from ._typing import _EntityType
+    from ._typing import _InternalEntityType
+    from .context import _MapperEntity
+    from .context import ORMCompileState
+    from .context import QueryContext
+    from .interfaces import _StrategyKey
+    from .interfaces import MapperProperty
+    from .interfaces import ORMOption
+    from .mapper import Mapper
+    from .path_registry import _PathRepresentation
+    from ..sql._typing import _ColumnExpressionArgument
+    from ..sql._typing import _FromClauseArgument
+    from ..sql.cache_key import _CacheKeyTraversalType
+    from ..sql.cache_key import CacheKey
+
+
+_AttrType = Union[Literal["*"], "QueryableAttribute[Any]"]
+
+_WildcardKeyType = Literal["relationship", "column"]
+_StrategySpec = Dict[str, Any]
+_OptsType = Dict[str, Any]
+_AttrGroupType = Tuple[_AttrType, ...]
+
+
+class _AbstractLoad(traversals.GenerativeOnTraversal, LoaderOption):
+    __slots__ = ("propagate_to_loaders",)
+
+    _is_strategy_option = True
+    propagate_to_loaders: bool
+
+    def contains_eager(
+        self,
+        attr: _AttrType,
+        alias: Optional[_FromClauseArgument] = None,
+        _is_chain: bool = False,
+    ) -> Self:
+        r"""Indicate that the given attribute should be eagerly loaded from
+        columns stated manually in the query.
+
+        This function is part of the :class:`_orm.Load` interface and supports
+        both method-chained and standalone operation.
+
+        The option is used in conjunction with an explicit join that loads
+        the desired rows, i.e.::
+
+            sess.query(Order).join(Order.user).options(
+                contains_eager(Order.user)
+            )
+
+        The above query would join from the ``Order`` entity to its related
+        ``User`` entity, and the returned ``Order`` objects would have the
+        ``Order.user`` attribute pre-populated.
+
+        It may also be used for customizing the entries in an eagerly loaded
+        collection; queries will normally want to use the
+        :ref:`orm_queryguide_populate_existing` execution option assuming the
+        primary collection of parent objects may already have been loaded::
+
+            sess.query(User).join(User.addresses).filter(
+                Address.email_address.like("%@aol.com")
+            ).options(contains_eager(User.addresses)).populate_existing()
+
+        See the section :ref:`contains_eager` for complete usage details.
+
+        .. seealso::
+
+            :ref:`loading_toplevel`
+
+            :ref:`contains_eager`
+
+        """
+        if alias is not None:
+            if not isinstance(alias, str):
+                coerced_alias = coercions.expect(roles.FromClauseRole, alias)
+            else:
+                util.warn_deprecated(
+                    "Passing a string name for the 'alias' argument to "
+                    "'contains_eager()` is deprecated, and will not work in a "
+                    "future release.  Please use a sqlalchemy.alias() or "
+                    "sqlalchemy.orm.aliased() construct.",
+                    version="1.4",
+                )
+                coerced_alias = alias
+
+        elif getattr(attr, "_of_type", None):
+            assert isinstance(attr, QueryableAttribute)
+            ot: Optional[_InternalEntityType[Any]] = inspect(attr._of_type)
+            assert ot is not None
+            coerced_alias = ot.selectable
+        else:
+            coerced_alias = None
+
+        cloned = self._set_relationship_strategy(
+            attr,
+            {"lazy": "joined"},
+            propagate_to_loaders=False,
+            opts={"eager_from_alias": coerced_alias},
+            _reconcile_to_other=True if _is_chain else None,
+        )
+        return cloned
+
+    def load_only(self, *attrs: _AttrType, raiseload: bool = False) -> Self:
+        r"""Indicate that for a particular entity, only the given list
+        of column-based attribute names should be loaded; all others will be
+        deferred.
+
+        This function is part of the :class:`_orm.Load` interface and supports
+        both method-chained and standalone operation.
+
+        Example - given a class ``User``, load only the ``name`` and
+        ``fullname`` attributes::
+
+            session.query(User).options(load_only(User.name, User.fullname))
+
+        Example - given a relationship ``User.addresses -> Address``, specify
+        subquery loading for the ``User.addresses`` collection, but on each
+        ``Address`` object load only the ``email_address`` attribute::
+
+            session.query(User).options(
+                subqueryload(User.addresses).load_only(Address.email_address)
+            )
+
+        For a statement that has multiple entities,
+        the lead entity can be
+        specifically referred to using the :class:`_orm.Load` constructor::
+
+            stmt = (
+                select(User, Address)
+                .join(User.addresses)
+                .options(
+                    Load(User).load_only(User.name, User.fullname),
+                    Load(Address).load_only(Address.email_address),
+                )
+            )
+
+        When used together with the
+        :ref:`populate_existing <orm_queryguide_populate_existing>`
+        execution option only the attributes listed will be refreshed.
+
+        :param \*attrs: Attributes to be loaded, all others will be deferred.
+
+        :param raiseload: raise :class:`.InvalidRequestError` rather than
+         lazy loading a value when a deferred attribute is accessed. Used
+         to prevent unwanted SQL from being emitted.
+
+         .. versionadded:: 2.0
+
+        .. seealso::
+
+            :ref:`orm_queryguide_column_deferral` - in the
+            :ref:`queryguide_toplevel`
+
+        :param \*attrs: Attributes to be loaded, all others will be deferred.
+
+        :param raiseload: raise :class:`.InvalidRequestError` rather than
+         lazy loading a value when a deferred attribute is accessed. Used
+         to prevent unwanted SQL from being emitted.
+
+         .. versionadded:: 2.0
+
+        """
+        cloned = self._set_column_strategy(
+            attrs,
+            {"deferred": False, "instrument": True},
+        )
+
+        wildcard_strategy = {"deferred": True, "instrument": True}
+        if raiseload:
+            wildcard_strategy["raiseload"] = True
+
+        cloned = cloned._set_column_strategy(
+            ("*",),
+            wildcard_strategy,
+        )
+        return cloned
+
+    def joinedload(
+        self,
+        attr: _AttrType,
+        innerjoin: Optional[bool] = None,
+    ) -> Self:
+        """Indicate that the given attribute should be loaded using joined
+        eager loading.
+
+        This function is part of the :class:`_orm.Load` interface and supports
+        both method-chained and standalone operation.
+
+        examples::
+
+            # joined-load the "orders" collection on "User"
+            select(User).options(joinedload(User.orders))
+
+            # joined-load Order.items and then Item.keywords
+            select(Order).options(
+                joinedload(Order.items).joinedload(Item.keywords)
+            )
+
+            # lazily load Order.items, but when Items are loaded,
+            # joined-load the keywords collection
+            select(Order).options(
+                lazyload(Order.items).joinedload(Item.keywords)
+            )
+
+        :param innerjoin: if ``True``, indicates that the joined eager load
+         should use an inner join instead of the default of left outer join::
+
+            select(Order).options(joinedload(Order.user, innerjoin=True))
+
+        In order to chain multiple eager joins together where some may be
+        OUTER and others INNER, right-nested joins are used to link them::
+
+            select(A).options(
+                joinedload(A.bs, innerjoin=False).joinedload(
+                    B.cs, innerjoin=True
+                )
+            )
+
+        The above query, linking A.bs via "outer" join and B.cs via "inner"
+        join would render the joins as "a LEFT OUTER JOIN (b JOIN c)". When
+        using older versions of SQLite (< 3.7.16), this form of JOIN is
+        translated to use full subqueries as this syntax is otherwise not
+        directly supported.
+
+        The ``innerjoin`` flag can also be stated with the term ``"unnested"``.
+        This indicates that an INNER JOIN should be used, *unless* the join
+        is linked to a LEFT OUTER JOIN to the left, in which case it
+        will render as LEFT OUTER JOIN.  For example, supposing ``A.bs``
+        is an outerjoin::
+
+            select(A).options(
+                joinedload(A.bs).joinedload(B.cs, innerjoin="unnested")
+            )
+
+
+        The above join will render as "a LEFT OUTER JOIN b LEFT OUTER JOIN c",
+        rather than as "a LEFT OUTER JOIN (b JOIN c)".
+
+        .. note:: The "unnested" flag does **not** affect the JOIN rendered
+            from a many-to-many association table, e.g. a table configured as
+            :paramref:`_orm.relationship.secondary`, to the target table; for
+            correctness of results, these joins are always INNER and are
+            therefore right-nested if linked to an OUTER join.
+
+        .. note::
+
+            The joins produced by :func:`_orm.joinedload` are **anonymously
+            aliased**. The criteria by which the join proceeds cannot be
+            modified, nor can the ORM-enabled :class:`_sql.Select` or legacy
+            :class:`_query.Query` refer to these joins in any way, including
+            ordering. See :ref:`zen_of_eager_loading` for further detail.
+
+            To produce a specific SQL JOIN which is explicitly available, use
+            :meth:`_sql.Select.join` and :meth:`_query.Query.join`. To combine
+            explicit JOINs with eager loading of collections, use
+            :func:`_orm.contains_eager`; see :ref:`contains_eager`.
+
+        .. seealso::
+
+            :ref:`loading_toplevel`
+
+            :ref:`joined_eager_loading`
+
+        """
+        loader = self._set_relationship_strategy(
+            attr,
+            {"lazy": "joined"},
+            opts=(
+                {"innerjoin": innerjoin}
+                if innerjoin is not None
+                else util.EMPTY_DICT
+            ),
+        )
+        return loader
+
+    def subqueryload(self, attr: _AttrType) -> Self:
+        """Indicate that the given attribute should be loaded using
+        subquery eager loading.
+
+        This function is part of the :class:`_orm.Load` interface and supports
+        both method-chained and standalone operation.
+
+        examples::
+
+            # subquery-load the "orders" collection on "User"
+            select(User).options(subqueryload(User.orders))
+
+            # subquery-load Order.items and then Item.keywords
+            select(Order).options(
+                subqueryload(Order.items).subqueryload(Item.keywords)
+            )
+
+            # lazily load Order.items, but when Items are loaded,
+            # subquery-load the keywords collection
+            select(Order).options(
+                lazyload(Order.items).subqueryload(Item.keywords)
+            )
+
+
+        .. seealso::
+
+            :ref:`loading_toplevel`
+
+            :ref:`subquery_eager_loading`
+
+        """
+        return self._set_relationship_strategy(attr, {"lazy": "subquery"})
+
+    def selectinload(
+        self,
+        attr: _AttrType,
+        recursion_depth: Optional[int] = None,
+    ) -> Self:
+        """Indicate that the given attribute should be loaded using
+        SELECT IN eager loading.
+
+        This function is part of the :class:`_orm.Load` interface and supports
+        both method-chained and standalone operation.
+
+        examples::
+
+            # selectin-load the "orders" collection on "User"
+            select(User).options(selectinload(User.orders))
+
+            # selectin-load Order.items and then Item.keywords
+            select(Order).options(
+                selectinload(Order.items).selectinload(Item.keywords)
+            )
+
+            # lazily load Order.items, but when Items are loaded,
+            # selectin-load the keywords collection
+            select(Order).options(
+                lazyload(Order.items).selectinload(Item.keywords)
+            )
+
+        :param recursion_depth: optional int; when set to a positive integer
+         in conjunction with a self-referential relationship,
+         indicates "selectin" loading will continue that many levels deep
+         automatically until no items are found.
+
+         .. note:: The :paramref:`_orm.selectinload.recursion_depth` option
+            currently supports only self-referential relationships.  There
+            is not yet an option to automatically traverse recursive structures
+            with more than one relationship involved.
+
+            Additionally, the :paramref:`_orm.selectinload.recursion_depth`
+            parameter is new and experimental and should be treated as "alpha"
+            status for the 2.0 series.
+
+         .. versionadded:: 2.0 added
+            :paramref:`_orm.selectinload.recursion_depth`
+
+
+        .. seealso::
+
+            :ref:`loading_toplevel`
+
+            :ref:`selectin_eager_loading`
+
+        """
+        return self._set_relationship_strategy(
+            attr,
+            {"lazy": "selectin"},
+            opts={"recursion_depth": recursion_depth},
+        )
+
+    def lazyload(self, attr: _AttrType) -> Self:
+        """Indicate that the given attribute should be loaded using "lazy"
+        loading.
+
+        This function is part of the :class:`_orm.Load` interface and supports
+        both method-chained and standalone operation.
+
+        .. seealso::
+
+            :ref:`loading_toplevel`
+
+            :ref:`lazy_loading`
+
+        """
+        return self._set_relationship_strategy(attr, {"lazy": "select"})
+
+    def immediateload(
+        self,
+        attr: _AttrType,
+        recursion_depth: Optional[int] = None,
+    ) -> Self:
+        """Indicate that the given attribute should be loaded using
+        an immediate load with a per-attribute SELECT statement.
+
+        The load is achieved using the "lazyloader" strategy and does not
+        fire off any additional eager loaders.
+
+        The :func:`.immediateload` option is superseded in general
+        by the :func:`.selectinload` option, which performs the same task
+        more efficiently by emitting a SELECT for all loaded objects.
+
+        This function is part of the :class:`_orm.Load` interface and supports
+        both method-chained and standalone operation.
+
+        :param recursion_depth: optional int; when set to a positive integer
+         in conjunction with a self-referential relationship,
+         indicates "selectin" loading will continue that many levels deep
+         automatically until no items are found.
+
+         .. note:: The :paramref:`_orm.immediateload.recursion_depth` option
+            currently supports only self-referential relationships.  There
+            is not yet an option to automatically traverse recursive structures
+            with more than one relationship involved.
+
+         .. warning:: This parameter is new and experimental and should be
+            treated as "alpha" status
+
+         .. versionadded:: 2.0 added
+            :paramref:`_orm.immediateload.recursion_depth`
+
+
+        .. seealso::
+
+            :ref:`loading_toplevel`
+
+            :ref:`selectin_eager_loading`
+
+        """
+        loader = self._set_relationship_strategy(
+            attr,
+            {"lazy": "immediate"},
+            opts={"recursion_depth": recursion_depth},
+        )
+        return loader
+
+    def noload(self, attr: _AttrType) -> Self:
+        """Indicate that the given relationship attribute should remain
+        unloaded.
+
+        The relationship attribute will return ``None`` when accessed without
+        producing any loading effect.
+
+        This function is part of the :class:`_orm.Load` interface and supports
+        both method-chained and standalone operation.
+
+        :func:`_orm.noload` applies to :func:`_orm.relationship` attributes
+        only.
+
+        .. note:: Setting this loading strategy as the default strategy
+            for a relationship using the :paramref:`.orm.relationship.lazy`
+            parameter may cause issues with flushes, such if a delete operation
+            needs to load related objects and instead ``None`` was returned.
+
+        .. seealso::
+
+            :ref:`loading_toplevel`
+
+        """
+
+        return self._set_relationship_strategy(attr, {"lazy": "noload"})
+
+    def raiseload(self, attr: _AttrType, sql_only: bool = False) -> Self:
+        """Indicate that the given attribute should raise an error if accessed.
+
+        A relationship attribute configured with :func:`_orm.raiseload` will
+        raise an :exc:`~sqlalchemy.exc.InvalidRequestError` upon access. The
+        typical way this is useful is when an application is attempting to
+        ensure that all relationship attributes that are accessed in a
+        particular context would have been already loaded via eager loading.
+        Instead of having to read through SQL logs to ensure lazy loads aren't
+        occurring, this strategy will cause them to raise immediately.
+
+        :func:`_orm.raiseload` applies to :func:`_orm.relationship` attributes
+        only. In order to apply raise-on-SQL behavior to a column-based
+        attribute, use the :paramref:`.orm.defer.raiseload` parameter on the
+        :func:`.defer` loader option.
+
+        :param sql_only: if True, raise only if the lazy load would emit SQL,
+         but not if it is only checking the identity map, or determining that
+         the related value should just be None due to missing keys. When False,
+         the strategy will raise for all varieties of relationship loading.
+
+        This function is part of the :class:`_orm.Load` interface and supports
+        both method-chained and standalone operation.
+
+        .. seealso::
+
+            :ref:`loading_toplevel`
+
+            :ref:`prevent_lazy_with_raiseload`
+
+            :ref:`orm_queryguide_deferred_raiseload`
+
+        """
+
+        return self._set_relationship_strategy(
+            attr, {"lazy": "raise_on_sql" if sql_only else "raise"}
+        )
+
+    def defaultload(self, attr: _AttrType) -> Self:
+        """Indicate an attribute should load using its predefined loader style.
+
+        The behavior of this loading option is to not change the current
+        loading style of the attribute, meaning that the previously configured
+        one is used or, if no previous style was selected, the default
+        loading will be used.
+
+        This method is used to link to other loader options further into
+        a chain of attributes without altering the loader style of the links
+        along the chain.  For example, to set joined eager loading for an
+        element of an element::
+
+            session.query(MyClass).options(
+                defaultload(MyClass.someattribute).joinedload(
+                    MyOtherClass.someotherattribute
+                )
+            )
+
+        :func:`.defaultload` is also useful for setting column-level options on
+        a related class, namely that of :func:`.defer` and :func:`.undefer`::
+
+            session.scalars(
+                select(MyClass).options(
+                    defaultload(MyClass.someattribute)
+                    .defer("some_column")
+                    .undefer("some_other_column")
+                )
+            )
+
+        .. seealso::
+
+            :ref:`orm_queryguide_relationship_sub_options`
+
+            :meth:`_orm.Load.options`
+
+        """
+        return self._set_relationship_strategy(attr, None)
+
+    def defer(self, key: _AttrType, raiseload: bool = False) -> Self:
+        r"""Indicate that the given column-oriented attribute should be
+        deferred, e.g. not loaded until accessed.
+
+        This function is part of the :class:`_orm.Load` interface and supports
+        both method-chained and standalone operation.
+
+        e.g.::
+
+            from sqlalchemy.orm import defer
+
+            session.query(MyClass).options(
+                defer(MyClass.attribute_one),
+                defer(MyClass.attribute_two)
+            )
+
+        To specify a deferred load of an attribute on a related class,
+        the path can be specified one token at a time, specifying the loading
+        style for each link along the chain.  To leave the loading style
+        for a link unchanged, use :func:`_orm.defaultload`::
+
+            session.query(MyClass).options(
+                defaultload(MyClass.someattr).defer(RelatedClass.some_column)
+            )
+
+        Multiple deferral options related to a relationship can be bundled
+        at once using :meth:`_orm.Load.options`::
+
+
+            select(MyClass).options(
+                defaultload(MyClass.someattr).options(
+                    defer(RelatedClass.some_column),
+                    defer(RelatedClass.some_other_column),
+                    defer(RelatedClass.another_column)
+                )
+            )
+
+        :param key: Attribute to be deferred.
+
+        :param raiseload: raise :class:`.InvalidRequestError` rather than
+         lazy loading a value when the deferred attribute is accessed. Used
+         to prevent unwanted SQL from being emitted.
+
+        .. versionadded:: 1.4
+
+        .. seealso::
+
+            :ref:`orm_queryguide_column_deferral` - in the
+            :ref:`queryguide_toplevel`
+
+            :func:`_orm.load_only`
+
+            :func:`_orm.undefer`
+
+        """
+        strategy = {"deferred": True, "instrument": True}
+        if raiseload:
+            strategy["raiseload"] = True
+        return self._set_column_strategy((key,), strategy)
+
+    def undefer(self, key: _AttrType) -> Self:
+        r"""Indicate that the given column-oriented attribute should be
+        undeferred, e.g. specified within the SELECT statement of the entity
+        as a whole.
+
+        The column being undeferred is typically set up on the mapping as a
+        :func:`.deferred` attribute.
+
+        This function is part of the :class:`_orm.Load` interface and supports
+        both method-chained and standalone operation.
+
+        Examples::
+
+            # undefer two columns
+            session.query(MyClass).options(
+                undefer(MyClass.col1), undefer(MyClass.col2)
+            )
+
+            # undefer all columns specific to a single class using Load + *
+            session.query(MyClass, MyOtherClass).options(
+                Load(MyClass).undefer("*")
+            )
+
+            # undefer a column on a related object
+            select(MyClass).options(
+                defaultload(MyClass.items).undefer(MyClass.text)
+            )
+
+        :param key: Attribute to be undeferred.
+
+        .. seealso::
+
+            :ref:`orm_queryguide_column_deferral` - in the
+            :ref:`queryguide_toplevel`
+
+            :func:`_orm.defer`
+
+            :func:`_orm.undefer_group`
+
+        """
+        return self._set_column_strategy(
+            (key,), {"deferred": False, "instrument": True}
+        )
+
+    def undefer_group(self, name: str) -> Self:
+        """Indicate that columns within the given deferred group name should be
+        undeferred.
+
+        The columns being undeferred are set up on the mapping as
+        :func:`.deferred` attributes and include a "group" name.
+
+        E.g::
+
+            session.query(MyClass).options(undefer_group("large_attrs"))
+
+        To undefer a group of attributes on a related entity, the path can be
+        spelled out using relationship loader options, such as
+        :func:`_orm.defaultload`::
+
+            select(MyClass).options(
+                defaultload("someattr").undefer_group("large_attrs")
+            )
+
+        .. seealso::
+
+            :ref:`orm_queryguide_column_deferral` - in the
+            :ref:`queryguide_toplevel`
+
+            :func:`_orm.defer`
+
+            :func:`_orm.undefer`
+
+        """
+        return self._set_column_strategy(
+            (_WILDCARD_TOKEN,), None, {f"undefer_group_{name}": True}
+        )
+
+    def with_expression(
+        self,
+        key: _AttrType,
+        expression: _ColumnExpressionArgument[Any],
+    ) -> Self:
+        r"""Apply an ad-hoc SQL expression to a "deferred expression"
+        attribute.
+
+        This option is used in conjunction with the
+        :func:`_orm.query_expression` mapper-level construct that indicates an
+        attribute which should be the target of an ad-hoc SQL expression.
+
+        E.g.::
+
+            stmt = select(SomeClass).options(
+                with_expression(SomeClass.x_y_expr, SomeClass.x + SomeClass.y)
+            )
+
+        .. versionadded:: 1.2
+
+        :param key: Attribute to be populated
+
+        :param expr: SQL expression to be applied to the attribute.
+
+        .. seealso::
+
+            :ref:`orm_queryguide_with_expression` - background and usage
+            examples
+
+        """
+
+        expression = _orm_full_deannotate(
+            coercions.expect(roles.LabeledColumnExprRole, expression)
+        )
+
+        return self._set_column_strategy(
+            (key,), {"query_expression": True}, extra_criteria=(expression,)
+        )
+
+    def selectin_polymorphic(self, classes: Iterable[Type[Any]]) -> Self:
+        """Indicate an eager load should take place for all attributes
+        specific to a subclass.
+
+        This uses an additional SELECT with IN against all matched primary
+        key values, and is the per-query analogue to the ``"selectin"``
+        setting on the :paramref:`.mapper.polymorphic_load` parameter.
+
+        .. versionadded:: 1.2
+
+        .. seealso::
+
+            :ref:`polymorphic_selectin`
+
+        """
+        self = self._set_class_strategy(
+            {"selectinload_polymorphic": True},
+            opts={
+                "entities": tuple(
+                    sorted((inspect(cls) for cls in classes), key=id)
+                )
+            },
+        )
+        return self
+
+    @overload
+    def _coerce_strat(self, strategy: _StrategySpec) -> _StrategyKey: ...
+
+    @overload
+    def _coerce_strat(self, strategy: Literal[None]) -> None: ...
+
+    def _coerce_strat(
+        self, strategy: Optional[_StrategySpec]
+    ) -> Optional[_StrategyKey]:
+        if strategy is not None:
+            strategy_key = tuple(sorted(strategy.items()))
+        else:
+            strategy_key = None
+        return strategy_key
+
+    @_generative
+    def _set_relationship_strategy(
+        self,
+        attr: _AttrType,
+        strategy: Optional[_StrategySpec],
+        propagate_to_loaders: bool = True,
+        opts: Optional[_OptsType] = None,
+        _reconcile_to_other: Optional[bool] = None,
+    ) -> Self:
+        strategy_key = self._coerce_strat(strategy)
+
+        self._clone_for_bind_strategy(
+            (attr,),
+            strategy_key,
+            _RELATIONSHIP_TOKEN,
+            opts=opts,
+            propagate_to_loaders=propagate_to_loaders,
+            reconcile_to_other=_reconcile_to_other,
+        )
+        return self
+
+    @_generative
+    def _set_column_strategy(
+        self,
+        attrs: Tuple[_AttrType, ...],
+        strategy: Optional[_StrategySpec],
+        opts: Optional[_OptsType] = None,
+        extra_criteria: Optional[Tuple[Any, ...]] = None,
+    ) -> Self:
+        strategy_key = self._coerce_strat(strategy)
+
+        self._clone_for_bind_strategy(
+            attrs,
+            strategy_key,
+            _COLUMN_TOKEN,
+            opts=opts,
+            attr_group=attrs,
+            extra_criteria=extra_criteria,
+        )
+        return self
+
+    @_generative
+    def _set_generic_strategy(
+        self,
+        attrs: Tuple[_AttrType, ...],
+        strategy: _StrategySpec,
+        _reconcile_to_other: Optional[bool] = None,
+    ) -> Self:
+        strategy_key = self._coerce_strat(strategy)
+        self._clone_for_bind_strategy(
+            attrs,
+            strategy_key,
+            None,
+            propagate_to_loaders=True,
+            reconcile_to_other=_reconcile_to_other,
+        )
+        return self
+
+    @_generative
+    def _set_class_strategy(
+        self, strategy: _StrategySpec, opts: _OptsType
+    ) -> Self:
+        strategy_key = self._coerce_strat(strategy)
+
+        self._clone_for_bind_strategy(None, strategy_key, None, opts=opts)
+        return self
+
+    def _apply_to_parent(self, parent: Load) -> None:
+        """apply this :class:`_orm._AbstractLoad` object as a sub-option o
+        a :class:`_orm.Load` object.
+
+        Implementation is provided by subclasses.
+
+        """
+        raise NotImplementedError()
+
+    def options(self, *opts: _AbstractLoad) -> Self:
+        r"""Apply a series of options as sub-options to this
+        :class:`_orm._AbstractLoad` object.
+
+        Implementation is provided by subclasses.
+
+        """
+        raise NotImplementedError()
+
+    def _clone_for_bind_strategy(
+        self,
+        attrs: Optional[Tuple[_AttrType, ...]],
+        strategy: Optional[_StrategyKey],
+        wildcard_key: Optional[_WildcardKeyType],
+        opts: Optional[_OptsType] = None,
+        attr_group: Optional[_AttrGroupType] = None,
+        propagate_to_loaders: bool = True,
+        reconcile_to_other: Optional[bool] = None,
+        extra_criteria: Optional[Tuple[Any, ...]] = None,
+    ) -> Self:
+        raise NotImplementedError()
+
+    def process_compile_state_replaced_entities(
+        self,
+        compile_state: ORMCompileState,
+        mapper_entities: Sequence[_MapperEntity],
+    ) -> None:
+        if not compile_state.compile_options._enable_eagerloads:
+            return
+
+        # process is being run here so that the options given are validated
+        # against what the lead entities were, as well as to accommodate
+        # for the entities having been replaced with equivalents
+        self._process(
+            compile_state,
+            mapper_entities,
+            not bool(compile_state.current_path),
+        )
+
+    def process_compile_state(self, compile_state: ORMCompileState) -> None:
+        if not compile_state.compile_options._enable_eagerloads:
+            return
+
+        self._process(
+            compile_state,
+            compile_state._lead_mapper_entities,
+            not bool(compile_state.current_path)
+            and not compile_state.compile_options._for_refresh_state,
+        )
+
+    def _process(
+        self,
+        compile_state: ORMCompileState,
+        mapper_entities: Sequence[_MapperEntity],
+        raiseerr: bool,
+    ) -> None:
+        """implemented by subclasses"""
+        raise NotImplementedError()
+
+    @classmethod
+    def _chop_path(
+        cls,
+        to_chop: _PathRepresentation,
+        path: PathRegistry,
+        debug: bool = False,
+    ) -> Optional[_PathRepresentation]:
+        i = -1
+
+        for i, (c_token, p_token) in enumerate(
+            zip(to_chop, path.natural_path)
+        ):
+            if isinstance(c_token, str):
+                if i == 0 and (
+                    c_token.endswith(f":{_DEFAULT_TOKEN}")
+                    or c_token.endswith(f":{_WILDCARD_TOKEN}")
+                ):
+                    return to_chop
+                elif (
+                    c_token != f"{_RELATIONSHIP_TOKEN}:{_WILDCARD_TOKEN}"
+                    and c_token != p_token.key  # type: ignore
+                ):
+                    return None
+
+            if c_token is p_token:
+                continue
+            elif (
+                isinstance(c_token, InspectionAttr)
+                and insp_is_mapper(c_token)
+                and insp_is_mapper(p_token)
+                and c_token.isa(p_token)
+            ):
+                continue
+
+            else:
+                return None
+        return to_chop[i + 1 :]
+
+
+class Load(_AbstractLoad):
+    """Represents loader options which modify the state of a
+    ORM-enabled :class:`_sql.Select` or a legacy :class:`_query.Query` in
+    order to affect how various mapped attributes are loaded.
+
+    The :class:`_orm.Load` object is in most cases used implicitly behind the
+    scenes when one makes use of a query option like :func:`_orm.joinedload`,
+    :func:`_orm.defer`, or similar.   It typically is not instantiated directly
+    except for in some very specific cases.
+
+    .. seealso::
+
+        :ref:`orm_queryguide_relationship_per_entity_wildcard` - illustrates an
+        example where direct use of :class:`_orm.Load` may be useful
+
+    """
+
+    __slots__ = (
+        "path",
+        "context",
+        "additional_source_entities",
+    )
+
+    _traverse_internals = [
+        ("path", visitors.ExtendedInternalTraversal.dp_has_cache_key),
+        (
+            "context",
+            visitors.InternalTraversal.dp_has_cache_key_list,
+        ),
+        ("propagate_to_loaders", visitors.InternalTraversal.dp_boolean),
+        (
+            "additional_source_entities",
+            visitors.InternalTraversal.dp_has_cache_key_list,
+        ),
+    ]
+    _cache_key_traversal = None
+
+    path: PathRegistry
+    context: Tuple[_LoadElement, ...]
+    additional_source_entities: Tuple[_InternalEntityType[Any], ...]
+
+    def __init__(self, entity: _EntityType[Any]):
+        insp = cast("Union[Mapper[Any], AliasedInsp[Any]]", inspect(entity))
+        insp._post_inspect
+
+        self.path = insp._path_registry
+        self.context = ()
+        self.propagate_to_loaders = False
+        self.additional_source_entities = ()
+
+    def __str__(self) -> str:
+        return f"Load({self.path[0]})"
+
+    @classmethod
+    def _construct_for_existing_path(
+        cls, path: AbstractEntityRegistry
+    ) -> Load:
+        load = cls.__new__(cls)
+        load.path = path
+        load.context = ()
+        load.propagate_to_loaders = False
+        load.additional_source_entities = ()
+        return load
+
+    def _adapt_cached_option_to_uncached_option(
+        self, context: QueryContext, uncached_opt: ORMOption
+    ) -> ORMOption:
+        if uncached_opt is self:
+            return self
+        return self._adjust_for_extra_criteria(context)
+
+    def _prepend_path(self, path: PathRegistry) -> Load:
+        cloned = self._clone()
+        cloned.context = tuple(
+            element._prepend_path(path) for element in self.context
+        )
+        return cloned
+
+    def _adjust_for_extra_criteria(self, context: QueryContext) -> Load:
+        """Apply the current bound parameters in a QueryContext to all
+        occurrences "extra_criteria" stored within this ``Load`` object,
+        returning a new instance of this ``Load`` object.
+
+        """
+
+        # avoid generating cache keys for the queries if we don't
+        # actually have any extra_criteria options, which is the
+        # common case
+        for value in self.context:
+            if value._extra_criteria:
+                break
+        else:
+            return self
+
+        replacement_cache_key = context.query._generate_cache_key()
+
+        if replacement_cache_key is None:
+            return self
+
+        orig_query = context.compile_state.select_statement
+        orig_cache_key = orig_query._generate_cache_key()
+        assert orig_cache_key is not None
+
+        def process(
+            opt: _LoadElement,
+            replacement_cache_key: CacheKey,
+            orig_cache_key: CacheKey,
+        ) -> _LoadElement:
+            cloned_opt = opt._clone()
+
+            cloned_opt._extra_criteria = tuple(
+                replacement_cache_key._apply_params_to_element(
+                    orig_cache_key, crit
+                )
+                for crit in cloned_opt._extra_criteria
+            )
+
+            return cloned_opt
+
+        cloned = self._clone()
+        cloned.context = tuple(
+            (
+                process(value, replacement_cache_key, orig_cache_key)
+                if value._extra_criteria
+                else value
+            )
+            for value in self.context
+        )
+        return cloned
+
+    def _reconcile_query_entities_with_us(self, mapper_entities, raiseerr):
+        """called at process time to allow adjustment of the root
+        entity inside of _LoadElement objects.
+
+        """
+        path = self.path
+
+        ezero = None
+        for ent in mapper_entities:
+            ezero = ent.entity_zero
+            if ezero and orm_util._entity_corresponds_to(
+                # technically this can be a token also, but this is
+                # safe to pass to _entity_corresponds_to()
+                ezero,
+                cast("_InternalEntityType[Any]", path[0]),
+            ):
+                return ezero
+
+        return None
+
+    def _process(
+        self,
+        compile_state: ORMCompileState,
+        mapper_entities: Sequence[_MapperEntity],
+        raiseerr: bool,
+    ) -> None:
+        reconciled_lead_entity = self._reconcile_query_entities_with_us(
+            mapper_entities, raiseerr
+        )
+
+        for loader in self.context:
+            loader.process_compile_state(
+                self,
+                compile_state,
+                mapper_entities,
+                reconciled_lead_entity,
+                raiseerr,
+            )
+
+    def _apply_to_parent(self, parent: Load) -> None:
+        """apply this :class:`_orm.Load` object as a sub-option of another
+        :class:`_orm.Load` object.
+
+        This method is used by the :meth:`_orm.Load.options` method.
+
+        """
+        cloned = self._generate()
+
+        assert cloned.propagate_to_loaders == self.propagate_to_loaders
+
+        if not any(
+            orm_util._entity_corresponds_to_use_path_impl(
+                elem, cloned.path.odd_element(0)
+            )
+            for elem in (parent.path.odd_element(-1),)
+            + parent.additional_source_entities
+        ):
+            if len(cloned.path) > 1:
+                attrname = cloned.path[1]
+                parent_entity = cloned.path[0]
+            else:
+                attrname = cloned.path[0]
+                parent_entity = cloned.path[0]
+            _raise_for_does_not_link(parent.path, attrname, parent_entity)
+
+        cloned.path = PathRegistry.coerce(parent.path[0:-1] + cloned.path[:])
+
+        if self.context:
+            cloned.context = tuple(
+                value._prepend_path_from(parent) for value in self.context
+            )
+
+        if cloned.context:
+            parent.context += cloned.context
+            parent.additional_source_entities += (
+                cloned.additional_source_entities
+            )
+
+    @_generative
+    def options(self, *opts: _AbstractLoad) -> Self:
+        r"""Apply a series of options as sub-options to this
+        :class:`_orm.Load`
+        object.
+
+        E.g.::
+
+            query = session.query(Author)
+            query = query.options(
+                        joinedload(Author.book).options(
+                            load_only(Book.summary, Book.excerpt),
+                            joinedload(Book.citations).options(
+                                joinedload(Citation.author)
+                            )
+                        )
+                    )
+
+        :param \*opts: A series of loader option objects (ultimately
+         :class:`_orm.Load` objects) which should be applied to the path
+         specified by this :class:`_orm.Load` object.
+
+        .. versionadded:: 1.3.6
+
+        .. seealso::
+
+            :func:`.defaultload`
+
+            :ref:`orm_queryguide_relationship_sub_options`
+
+        """
+        for opt in opts:
+            try:
+                opt._apply_to_parent(self)
+            except AttributeError as ae:
+                if not isinstance(opt, _AbstractLoad):
+                    raise sa_exc.ArgumentError(
+                        f"Loader option {opt} is not compatible with the "
+                        "Load.options() method."
+                    ) from ae
+                else:
+                    raise
+        return self
+
+    def _clone_for_bind_strategy(
+        self,
+        attrs: Optional[Tuple[_AttrType, ...]],
+        strategy: Optional[_StrategyKey],
+        wildcard_key: Optional[_WildcardKeyType],
+        opts: Optional[_OptsType] = None,
+        attr_group: Optional[_AttrGroupType] = None,
+        propagate_to_loaders: bool = True,
+        reconcile_to_other: Optional[bool] = None,
+        extra_criteria: Optional[Tuple[Any, ...]] = None,
+    ) -> Self:
+        # for individual strategy that needs to propagate, set the whole
+        # Load container to also propagate, so that it shows up in
+        # InstanceState.load_options
+        if propagate_to_loaders:
+            self.propagate_to_loaders = True
+
+        if self.path.is_token:
+            raise sa_exc.ArgumentError(
+                "Wildcard token cannot be followed by another entity"
+            )
+
+        elif path_is_property(self.path):
+            # re-use the lookup which will raise a nicely formatted
+            # LoaderStrategyException
+            if strategy:
+                self.path.prop._strategy_lookup(self.path.prop, strategy[0])
+            else:
+                raise sa_exc.ArgumentError(
+                    f"Mapped attribute '{self.path.prop}' does not "
+                    "refer to a mapped entity"
+                )
+
+        if attrs is None:
+            load_element = _ClassStrategyLoad.create(
+                self.path,
+                None,
+                strategy,
+                wildcard_key,
+                opts,
+                propagate_to_loaders,
+                attr_group=attr_group,
+                reconcile_to_other=reconcile_to_other,
+                extra_criteria=extra_criteria,
+            )
+            if load_element:
+                self.context += (load_element,)
+                assert opts is not None
+                self.additional_source_entities += cast(
+                    "Tuple[_InternalEntityType[Any]]", opts["entities"]
+                )
+
+        else:
+            for attr in attrs:
+                if isinstance(attr, str):
+                    load_element = _TokenStrategyLoad.create(
+                        self.path,
+                        attr,
+                        strategy,
+                        wildcard_key,
+                        opts,
+                        propagate_to_loaders,
+                        attr_group=attr_group,
+                        reconcile_to_other=reconcile_to_other,
+                        extra_criteria=extra_criteria,
+                    )
+                else:
+                    load_element = _AttributeStrategyLoad.create(
+                        self.path,
+                        attr,
+                        strategy,
+                        wildcard_key,
+                        opts,
+                        propagate_to_loaders,
+                        attr_group=attr_group,
+                        reconcile_to_other=reconcile_to_other,
+                        extra_criteria=extra_criteria,
+                    )
+
+                if load_element:
+                    # for relationship options, update self.path on this Load
+                    # object with the latest path.
+                    if wildcard_key is _RELATIONSHIP_TOKEN:
+                        self.path = load_element.path
+                    self.context += (load_element,)
+
+                    # this seems to be effective for selectinloader,
+                    # giving the extra match to one more level deep.
+                    # but does not work for immediateloader, which still
+                    # must add additional options at load time
+                    if load_element.local_opts.get("recursion_depth", False):
+                        r1 = load_element._recurse()
+                        self.context += (r1,)
+
+        return self
+
+    def __getstate__(self):
+        d = self._shallow_to_dict()
+        d["path"] = self.path.serialize()
+        return d
+
+    def __setstate__(self, state):
+        state["path"] = PathRegistry.deserialize(state["path"])
+        self._shallow_from_dict(state)
+
+
+class _WildcardLoad(_AbstractLoad):
+    """represent a standalone '*' load operation"""
+
+    __slots__ = ("strategy", "path", "local_opts")
+
+    _traverse_internals = [
+        ("strategy", visitors.ExtendedInternalTraversal.dp_plain_obj),
+        ("path", visitors.ExtendedInternalTraversal.dp_plain_obj),
+        (
+            "local_opts",
+            visitors.ExtendedInternalTraversal.dp_string_multi_dict,
+        ),
+    ]
+    cache_key_traversal: _CacheKeyTraversalType = None
+
+    strategy: Optional[Tuple[Any, ...]]
+    local_opts: _OptsType
+    path: Union[Tuple[()], Tuple[str]]
+    propagate_to_loaders = False
+
+    def __init__(self) -> None:
+        self.path = ()
+        self.strategy = None
+        self.local_opts = util.EMPTY_DICT
+
+    def _clone_for_bind_strategy(
+        self,
+        attrs,
+        strategy,
+        wildcard_key,
+        opts=None,
+        attr_group=None,
+        propagate_to_loaders=True,
+        reconcile_to_other=None,
+        extra_criteria=None,
+    ):
+        assert attrs is not None
+        attr = attrs[0]
+        assert (
+            wildcard_key
+            and isinstance(attr, str)
+            and attr in (_WILDCARD_TOKEN, _DEFAULT_TOKEN)
+        )
+
+        attr = f"{wildcard_key}:{attr}"
+
+        self.strategy = strategy
+        self.path = (attr,)
+        if opts:
+            self.local_opts = util.immutabledict(opts)
+
+        assert extra_criteria is None
+
+    def options(self, *opts: _AbstractLoad) -> Self:
+        raise NotImplementedError("Star option does not support sub-options")
+
+    def _apply_to_parent(self, parent: Load) -> None:
+        """apply this :class:`_orm._WildcardLoad` object as a sub-option of
+        a :class:`_orm.Load` object.
+
+        This method is used by the :meth:`_orm.Load.options` method.   Note
+        that :class:`_orm.WildcardLoad` itself can't have sub-options, but
+        it may be used as the sub-option of a :class:`_orm.Load` object.
+
+        """
+        assert self.path
+        attr = self.path[0]
+        if attr.endswith(_DEFAULT_TOKEN):
+            attr = f"{attr.split(':')[0]}:{_WILDCARD_TOKEN}"
+
+        effective_path = cast(AbstractEntityRegistry, parent.path).token(attr)
+
+        assert effective_path.is_token
+
+        loader = _TokenStrategyLoad.create(
+            effective_path,
+            None,
+            self.strategy,
+            None,
+            self.local_opts,
+            self.propagate_to_loaders,
+        )
+
+        parent.context += (loader,)
+
+    def _process(self, compile_state, mapper_entities, raiseerr):
+        is_refresh = compile_state.compile_options._for_refresh_state
+
+        if is_refresh and not self.propagate_to_loaders:
+            return
+
+        entities = [ent.entity_zero for ent in mapper_entities]
+        current_path = compile_state.current_path
+
+        start_path: _PathRepresentation = self.path
+
+        if current_path:
+            # TODO: no cases in test suite where we actually get
+            # None back here
+            new_path = self._chop_path(start_path, current_path)
+            if new_path is None:
+                return
+
+            # chop_path does not actually "chop" a wildcard token path,
+            # just returns it
+            assert new_path == start_path
+
+        # start_path is a single-token tuple
+        assert start_path and len(start_path) == 1
+
+        token = start_path[0]
+        assert isinstance(token, str)
+        entity = self._find_entity_basestring(entities, token, raiseerr)
+
+        if not entity:
+            return
+
+        path_element = entity
+
+        # transfer our entity-less state into a Load() object
+        # with a real entity path.  Start with the lead entity
+        # we just located, then go through the rest of our path
+        # tokens and populate into the Load().
+
+        assert isinstance(token, str)
+        loader = _TokenStrategyLoad.create(
+            path_element._path_registry,
+            token,
+            self.strategy,
+            None,
+            self.local_opts,
+            self.propagate_to_loaders,
+            raiseerr=raiseerr,
+        )
+        if not loader:
+            return
+
+        assert loader.path.is_token
+
+        # don't pass a reconciled lead entity here
+        loader.process_compile_state(
+            self, compile_state, mapper_entities, None, raiseerr
+        )
+
+        return loader
+
+    def _find_entity_basestring(
+        self,
+        entities: Iterable[_InternalEntityType[Any]],
+        token: str,
+        raiseerr: bool,
+    ) -> Optional[_InternalEntityType[Any]]:
+        if token.endswith(f":{_WILDCARD_TOKEN}"):
+            if len(list(entities)) != 1:
+                if raiseerr:
+                    raise sa_exc.ArgumentError(
+                        "Can't apply wildcard ('*') or load_only() "
+                        f"loader option to multiple entities "
+                        f"{', '.join(str(ent) for ent in entities)}. Specify "
+                        "loader options for each entity individually, such as "
+                        f"""{
+                            ", ".join(
+                                f"Load({ent}).some_option('*')"
+                                for ent in entities
+                            )
+                        }."""
+                    )
+        elif token.endswith(_DEFAULT_TOKEN):
+            raiseerr = False
+
+        for ent in entities:
+            # return only the first _MapperEntity when searching
+            # based on string prop name.   Ideally object
+            # attributes are used to specify more exactly.
+            return ent
+        else:
+            if raiseerr:
+                raise sa_exc.ArgumentError(
+                    "Query has only expression-based entities - "
+                    f'can\'t find property named "{token}".'
+                )
+            else:
+                return None
+
+    def __getstate__(self) -> Dict[str, Any]:
+        d = self._shallow_to_dict()
+        return d
+
+    def __setstate__(self, state: Dict[str, Any]) -> None:
+        self._shallow_from_dict(state)
+
+
+class _LoadElement(
+    cache_key.HasCacheKey, traversals.HasShallowCopy, visitors.Traversible
+):
+    """represents strategy information to select for a LoaderStrategy
+    and pass options to it.
+
+    :class:`._LoadElement` objects provide the inner datastructure
+    stored by a :class:`_orm.Load` object and are also the object passed
+    to methods like :meth:`.LoaderStrategy.setup_query`.
+
+    .. versionadded:: 2.0
+
+    """
+
+    __slots__ = (
+        "path",
+        "strategy",
+        "propagate_to_loaders",
+        "local_opts",
+        "_extra_criteria",
+        "_reconcile_to_other",
+    )
+    __visit_name__ = "load_element"
+
+    _traverse_internals = [
+        ("path", visitors.ExtendedInternalTraversal.dp_has_cache_key),
+        ("strategy", visitors.ExtendedInternalTraversal.dp_plain_obj),
+        (
+            "local_opts",
+            visitors.ExtendedInternalTraversal.dp_string_multi_dict,
+        ),
+        ("_extra_criteria", visitors.InternalTraversal.dp_clauseelement_list),
+        ("propagate_to_loaders", visitors.InternalTraversal.dp_plain_obj),
+        ("_reconcile_to_other", visitors.InternalTraversal.dp_plain_obj),
+    ]
+    _cache_key_traversal = None
+
+    _extra_criteria: Tuple[Any, ...]
+
+    _reconcile_to_other: Optional[bool]
+    strategy: Optional[_StrategyKey]
+    path: PathRegistry
+    propagate_to_loaders: bool
+
+    local_opts: util.immutabledict[str, Any]
+
+    is_token_strategy: bool
+    is_class_strategy: bool
+
+    def __hash__(self) -> int:
+        return id(self)
+
+    def __eq__(self, other):
+        return traversals.compare(self, other)
+
+    @property
+    def is_opts_only(self) -> bool:
+        return bool(self.local_opts and self.strategy is None)
+
+    def _clone(self, **kw: Any) -> _LoadElement:
+        cls = self.__class__
+        s = cls.__new__(cls)
+
+        self._shallow_copy_to(s)
+        return s
+
+    def _update_opts(self, **kw: Any) -> _LoadElement:
+        new = self._clone()
+        new.local_opts = new.local_opts.union(kw)
+        return new
+
+    def __getstate__(self) -> Dict[str, Any]:
+        d = self._shallow_to_dict()
+        d["path"] = self.path.serialize()
+        return d
+
+    def __setstate__(self, state: Dict[str, Any]) -> None:
+        state["path"] = PathRegistry.deserialize(state["path"])
+        self._shallow_from_dict(state)
+
+    def _raise_for_no_match(self, parent_loader, mapper_entities):
+        path = parent_loader.path
+
+        found_entities = False
+        for ent in mapper_entities:
+            ezero = ent.entity_zero
+            if ezero:
+                found_entities = True
+                break
+
+        if not found_entities:
+            raise sa_exc.ArgumentError(
+                "Query has only expression-based entities; "
+                f"attribute loader options for {path[0]} can't "
+                "be applied here."
+            )
+        else:
+            raise sa_exc.ArgumentError(
+                f"Mapped class {path[0]} does not apply to any of the "
+                f"root entities in this query, e.g. "
+                f"""{
+                    ", ".join(
+                        str(x.entity_zero)
+                        for x in mapper_entities if x.entity_zero
+                    )}. Please """
+                "specify the full path "
+                "from one of the root entities to the target "
+                "attribute. "
+            )
+
+    def _adjust_effective_path_for_current_path(
+        self, effective_path: PathRegistry, current_path: PathRegistry
+    ) -> Optional[PathRegistry]:
+        """receives the 'current_path' entry from an :class:`.ORMCompileState`
+        instance, which is set during lazy loads and secondary loader strategy
+        loads, and adjusts the given path to be relative to the
+        current_path.
+
+        E.g. given a loader path and current path::
+
+            lp: User -> orders -> Order -> items -> Item -> keywords -> Keyword
+
+            cp: User -> orders -> Order -> items
+
+        The adjusted path would be::
+
+            Item -> keywords -> Keyword
+
+
+        """
+        chopped_start_path = Load._chop_path(
+            effective_path.natural_path, current_path
+        )
+        if not chopped_start_path:
+            return None
+
+        tokens_removed_from_start_path = len(effective_path) - len(
+            chopped_start_path
+        )
+
+        loader_lead_path_element = self.path[tokens_removed_from_start_path]
+
+        effective_path = PathRegistry.coerce(
+            (loader_lead_path_element,) + chopped_start_path[1:]
+        )
+
+        return effective_path
+
+    def _init_path(
+        self, path, attr, wildcard_key, attr_group, raiseerr, extra_criteria
+    ):
+        """Apply ORM attributes and/or wildcard to an existing path, producing
+        a new path.
+
+        This method is used within the :meth:`.create` method to initialize
+        a :class:`._LoadElement` object.
+
+        """
+        raise NotImplementedError()
+
+    def _prepare_for_compile_state(
+        self,
+        parent_loader,
+        compile_state,
+        mapper_entities,
+        reconciled_lead_entity,
+        raiseerr,
+    ):
+        """implemented by subclasses."""
+        raise NotImplementedError()
+
+    def process_compile_state(
+        self,
+        parent_loader,
+        compile_state,
+        mapper_entities,
+        reconciled_lead_entity,
+        raiseerr,
+    ):
+        """populate ORMCompileState.attributes with loader state for this
+        _LoadElement.
+
+        """
+        keys = self._prepare_for_compile_state(
+            parent_loader,
+            compile_state,
+            mapper_entities,
+            reconciled_lead_entity,
+            raiseerr,
+        )
+        for key in keys:
+            if key in compile_state.attributes:
+                compile_state.attributes[key] = _LoadElement._reconcile(
+                    self, compile_state.attributes[key]
+                )
+            else:
+                compile_state.attributes[key] = self
+
+    @classmethod
+    def create(
+        cls,
+        path: PathRegistry,
+        attr: Union[_AttrType, _StrPathToken, None],
+        strategy: Optional[_StrategyKey],
+        wildcard_key: Optional[_WildcardKeyType],
+        local_opts: Optional[_OptsType],
+        propagate_to_loaders: bool,
+        raiseerr: bool = True,
+        attr_group: Optional[_AttrGroupType] = None,
+        reconcile_to_other: Optional[bool] = None,
+        extra_criteria: Optional[Tuple[Any, ...]] = None,
+    ) -> _LoadElement:
+        """Create a new :class:`._LoadElement` object."""
+
+        opt = cls.__new__(cls)
+        opt.path = path
+        opt.strategy = strategy
+        opt.propagate_to_loaders = propagate_to_loaders
+        opt.local_opts = (
+            util.immutabledict(local_opts) if local_opts else util.EMPTY_DICT
+        )
+        opt._extra_criteria = ()
+
+        if reconcile_to_other is not None:
+            opt._reconcile_to_other = reconcile_to_other
+        elif strategy is None and not local_opts:
+            opt._reconcile_to_other = True
+        else:
+            opt._reconcile_to_other = None
+
+        path = opt._init_path(
+            path, attr, wildcard_key, attr_group, raiseerr, extra_criteria
+        )
+
+        if not path:
+            return None  # type: ignore
+
+        assert opt.is_token_strategy == path.is_token
+
+        opt.path = path
+        return opt
+
+    def __init__(self) -> None:
+        raise NotImplementedError()
+
+    def _recurse(self) -> _LoadElement:
+        cloned = self._clone()
+        cloned.path = PathRegistry.coerce(self.path[:] + self.path[-2:])
+
+        return cloned
+
+    def _prepend_path_from(self, parent: Load) -> _LoadElement:
+        """adjust the path of this :class:`._LoadElement` to be
+        a subpath of that of the given parent :class:`_orm.Load` object's
+        path.
+
+        This is used by the :meth:`_orm.Load._apply_to_parent` method,
+        which is in turn part of the :meth:`_orm.Load.options` method.
+
+        """
+
+        if not any(
+            orm_util._entity_corresponds_to_use_path_impl(
+                elem,
+                self.path.odd_element(0),
+            )
+            for elem in (parent.path.odd_element(-1),)
+            + parent.additional_source_entities
+        ):
+            raise sa_exc.ArgumentError(
+                f'Attribute "{self.path[1]}" does not link '
+                f'from element "{parent.path[-1]}".'
+            )
+
+        return self._prepend_path(parent.path)
+
+    def _prepend_path(self, path: PathRegistry) -> _LoadElement:
+        cloned = self._clone()
+
+        assert cloned.strategy == self.strategy
+        assert cloned.local_opts == self.local_opts
+        assert cloned.is_class_strategy == self.is_class_strategy
+
+        cloned.path = PathRegistry.coerce(path[0:-1] + cloned.path[:])
+
+        return cloned
+
+    @staticmethod
+    def _reconcile(
+        replacement: _LoadElement, existing: _LoadElement
+    ) -> _LoadElement:
+        """define behavior for when two Load objects are to be put into
+        the context.attributes under the same key.
+
+        :param replacement: ``_LoadElement`` that seeks to replace the
+         existing one
+
+        :param existing: ``_LoadElement`` that is already present.
+
+        """
+        # mapper inheritance loading requires fine-grained "block other
+        # options" / "allow these options to be overridden" behaviors
+        # see test_poly_loading.py
+
+        if replacement._reconcile_to_other:
+            return existing
+        elif replacement._reconcile_to_other is False:
+            return replacement
+        elif existing._reconcile_to_other:
+            return replacement
+        elif existing._reconcile_to_other is False:
+            return existing
+
+        if existing is replacement:
+            return replacement
+        elif (
+            existing.strategy == replacement.strategy
+            and existing.local_opts == replacement.local_opts
+        ):
+            return replacement
+        elif replacement.is_opts_only:
+            existing = existing._clone()
+            existing.local_opts = existing.local_opts.union(
+                replacement.local_opts
+            )
+            existing._extra_criteria += replacement._extra_criteria
+            return existing
+        elif existing.is_opts_only:
+            replacement = replacement._clone()
+            replacement.local_opts = replacement.local_opts.union(
+                existing.local_opts
+            )
+            replacement._extra_criteria += existing._extra_criteria
+            return replacement
+        elif replacement.path.is_token:
+            # use 'last one wins' logic for wildcard options.  this is also
+            # kind of inconsistent vs. options that are specific paths which
+            # will raise as below
+            return replacement
+
+        raise sa_exc.InvalidRequestError(
+            f"Loader strategies for {replacement.path} conflict"
+        )
+
+
+class _AttributeStrategyLoad(_LoadElement):
+    """Loader strategies against specific relationship or column paths.
+
+    e.g.::
+
+        joinedload(User.addresses)
+        defer(Order.name)
+        selectinload(User.orders).lazyload(Order.items)
+
+    """
+
+    __slots__ = ("_of_type", "_path_with_polymorphic_path")
+
+    __visit_name__ = "attribute_strategy_load_element"
+
+    _traverse_internals = _LoadElement._traverse_internals + [
+        ("_of_type", visitors.ExtendedInternalTraversal.dp_multi),
+        (
+            "_path_with_polymorphic_path",
+            visitors.ExtendedInternalTraversal.dp_has_cache_key,
+        ),
+    ]
+
+    _of_type: Union[Mapper[Any], AliasedInsp[Any], None]
+    _path_with_polymorphic_path: Optional[PathRegistry]
+
+    is_class_strategy = False
+    is_token_strategy = False
+
+    def _init_path(
+        self, path, attr, wildcard_key, attr_group, raiseerr, extra_criteria
+    ):
+        assert attr is not None
+        self._of_type = None
+        self._path_with_polymorphic_path = None
+        insp, _, prop = _parse_attr_argument(attr)
+
+        if insp.is_property:
+            # direct property can be sent from internal strategy logic
+            # that sets up specific loaders, such as
+            # emit_lazyload->_lazyload_reverse
+            # prop = found_property = attr
+            prop = attr
+            path = path[prop]
+
+            if path.has_entity:
+                path = path.entity_path
+            return path
+
+        elif not insp.is_attribute:
+            # should not reach here;
+            assert False
+
+        # here we assume we have user-passed InstrumentedAttribute
+        if not orm_util._entity_corresponds_to_use_path_impl(
+            path[-1], attr.parent
+        ):
+            if raiseerr:
+                if attr_group and attr is not attr_group[0]:
+                    raise sa_exc.ArgumentError(
+                        "Can't apply wildcard ('*') or load_only() "
+                        "loader option to multiple entities in the "
+                        "same option. Use separate options per entity."
+                    )
+                else:
+                    _raise_for_does_not_link(path, str(attr), attr.parent)
+            else:
+                return None
+
+        # note the essential logic of this attribute was very different in
+        # 1.4, where there were caching failures in e.g.
+        # test_relationship_criteria.py::RelationshipCriteriaTest::
+        # test_selectinload_nested_criteria[True] if an existing
+        # "_extra_criteria" on a Load object were replaced with that coming
+        # from an attribute.   This appears to have been an artifact of how
+        # _UnboundLoad / Load interacted together, which was opaque and
+        # poorly defined.
+        if extra_criteria:
+            assert not attr._extra_criteria
+            self._extra_criteria = extra_criteria
+        else:
+            self._extra_criteria = attr._extra_criteria
+
+        if getattr(attr, "_of_type", None):
+            ac = attr._of_type
+            ext_info = inspect(ac)
+            self._of_type = ext_info
+
+            self._path_with_polymorphic_path = path.entity_path[prop]
+
+            path = path[prop][ext_info]
+
+        else:
+            path = path[prop]
+
+        if path.has_entity:
+            path = path.entity_path
+
+        return path
+
+    def _generate_extra_criteria(self, context):
+        """Apply the current bound parameters in a QueryContext to the
+        immediate "extra_criteria" stored with this Load object.
+
+        Load objects are typically pulled from the cached version of
+        the statement from a QueryContext.  The statement currently being
+        executed will have new values (and keys) for bound parameters in the
+        extra criteria which need to be applied by loader strategies when
+        they handle this criteria for a result set.
+
+        """
+
+        assert (
+            self._extra_criteria
+        ), "this should only be called if _extra_criteria is present"
+
+        orig_query = context.compile_state.select_statement
+        current_query = context.query
+
+        # NOTE: while it seems like we should not do the "apply" operation
+        # here if orig_query is current_query, skipping it in the "optimized"
+        # case causes the query to be different from a cache key perspective,
+        # because we are creating a copy of the criteria which is no longer
+        # the same identity of the _extra_criteria in the loader option
+        # itself.  cache key logic produces a different key for
+        # (A, copy_of_A) vs. (A, A), because in the latter case it shortens
+        # the second part of the key to just indicate on identity.
+
+        # if orig_query is current_query:
+        # not cached yet.   just do the and_()
+        #    return and_(*self._extra_criteria)
+
+        k1 = orig_query._generate_cache_key()
+        k2 = current_query._generate_cache_key()
+
+        return k2._apply_params_to_element(k1, and_(*self._extra_criteria))
+
+    def _set_of_type_info(self, context, current_path):
+        assert self._path_with_polymorphic_path
+
+        pwpi = self._of_type
+        assert pwpi
+        if not pwpi.is_aliased_class:
+            pwpi = inspect(
+                orm_util.AliasedInsp._with_polymorphic_factory(
+                    pwpi.mapper.base_mapper,
+                    (pwpi.mapper,),
+                    aliased=True,
+                    _use_mapper_path=True,
+                )
+            )
+        start_path = self._path_with_polymorphic_path
+        if current_path:
+            new_path = self._adjust_effective_path_for_current_path(
+                start_path, current_path
+            )
+            if new_path is None:
+                return
+            start_path = new_path
+
+        key = ("path_with_polymorphic", start_path.natural_path)
+        if key in context:
+            existing_aliased_insp = context[key]
+            this_aliased_insp = pwpi
+            new_aliased_insp = existing_aliased_insp._merge_with(
+                this_aliased_insp
+            )
+            context[key] = new_aliased_insp
+        else:
+            context[key] = pwpi
+
+    def _prepare_for_compile_state(
+        self,
+        parent_loader,
+        compile_state,
+        mapper_entities,
+        reconciled_lead_entity,
+        raiseerr,
+    ):
+        # _AttributeStrategyLoad
+
+        current_path = compile_state.current_path
+        is_refresh = compile_state.compile_options._for_refresh_state
+        assert not self.path.is_token
+
+        if is_refresh and not self.propagate_to_loaders:
+            return []
+
+        if self._of_type:
+            # apply additional with_polymorphic alias that may have been
+            # generated.  this has to happen even if this is a defaultload
+            self._set_of_type_info(compile_state.attributes, current_path)
+
+        # omit setting loader attributes for a "defaultload" type of option
+        if not self.strategy and not self.local_opts:
+            return []
+
+        if raiseerr and not reconciled_lead_entity:
+            self._raise_for_no_match(parent_loader, mapper_entities)
+
+        if self.path.has_entity:
+            effective_path = self.path.parent
+        else:
+            effective_path = self.path
+
+        if current_path:
+            assert effective_path is not None
+            effective_path = self._adjust_effective_path_for_current_path(
+                effective_path, current_path
+            )
+            if effective_path is None:
+                return []
+
+        return [("loader", cast(PathRegistry, effective_path).natural_path)]
+
+    def __getstate__(self):
+        d = super().__getstate__()
+
+        # can't pickle this.  See
+        # test_pickled.py -> test_lazyload_extra_criteria_not_supported
+        # where we should be emitting a warning for the usual case where this
+        # would be non-None
+        d["_extra_criteria"] = ()
+
+        if self._path_with_polymorphic_path:
+            d["_path_with_polymorphic_path"] = (
+                self._path_with_polymorphic_path.serialize()
+            )
+
+        if self._of_type:
+            if self._of_type.is_aliased_class:
+                d["_of_type"] = None
+            elif self._of_type.is_mapper:
+                d["_of_type"] = self._of_type.class_
+            else:
+                assert False, "unexpected object for _of_type"
+
+        return d
+
+    def __setstate__(self, state):
+        super().__setstate__(state)
+
+        if state.get("_path_with_polymorphic_path", None):
+            self._path_with_polymorphic_path = PathRegistry.deserialize(
+                state["_path_with_polymorphic_path"]
+            )
+        else:
+            self._path_with_polymorphic_path = None
+
+        if state.get("_of_type", None):
+            self._of_type = inspect(state["_of_type"])
+        else:
+            self._of_type = None
+
+
+class _TokenStrategyLoad(_LoadElement):
+    """Loader strategies against wildcard attributes
+
+    e.g.::
+
+        raiseload('*')
+        Load(User).lazyload('*')
+        defer('*')
+        load_only(User.name, User.email)  # will create a defer('*')
+        joinedload(User.addresses).raiseload('*')
+
+    """
+
+    __visit_name__ = "token_strategy_load_element"
+
+    inherit_cache = True
+    is_class_strategy = False
+    is_token_strategy = True
+
+    def _init_path(
+        self, path, attr, wildcard_key, attr_group, raiseerr, extra_criteria
+    ):
+        # assert isinstance(attr, str) or attr is None
+        if attr is not None:
+            default_token = attr.endswith(_DEFAULT_TOKEN)
+            if attr.endswith(_WILDCARD_TOKEN) or default_token:
+                if wildcard_key:
+                    attr = f"{wildcard_key}:{attr}"
+
+                path = path.token(attr)
+                return path
+            else:
+                raise sa_exc.ArgumentError(
+                    "Strings are not accepted for attribute names in loader "
+                    "options; please use class-bound attributes directly."
+                )
+        return path
+
+    def _prepare_for_compile_state(
+        self,
+        parent_loader,
+        compile_state,
+        mapper_entities,
+        reconciled_lead_entity,
+        raiseerr,
+    ):
+        # _TokenStrategyLoad
+
+        current_path = compile_state.current_path
+        is_refresh = compile_state.compile_options._for_refresh_state
+
+        assert self.path.is_token
+
+        if is_refresh and not self.propagate_to_loaders:
+            return []
+
+        # omit setting attributes for a "defaultload" type of option
+        if not self.strategy and not self.local_opts:
+            return []
+
+        effective_path = self.path
+        if reconciled_lead_entity:
+            effective_path = PathRegistry.coerce(
+                (reconciled_lead_entity,) + effective_path.path[1:]
+            )
+
+        if current_path:
+            new_effective_path = self._adjust_effective_path_for_current_path(
+                effective_path, current_path
+            )
+            if new_effective_path is None:
+                return []
+            effective_path = new_effective_path
+
+        # for a wildcard token, expand out the path we set
+        # to encompass everything from the query entity on
+        # forward.  not clear if this is necessary when current_path
+        # is set.
+
+        return [
+            ("loader", natural_path)
+            for natural_path in (
+                cast(
+                    TokenRegistry, effective_path
+                )._generate_natural_for_superclasses()
+            )
+        ]
+
+
+class _ClassStrategyLoad(_LoadElement):
+    """Loader strategies that deals with a class as a target, not
+    an attribute path
+
+    e.g.::
+
+        q = s.query(Person).options(
+            selectin_polymorphic(Person, [Engineer, Manager])
+        )
+
+    """
+
+    inherit_cache = True
+    is_class_strategy = True
+    is_token_strategy = False
+
+    __visit_name__ = "class_strategy_load_element"
+
+    def _init_path(
+        self, path, attr, wildcard_key, attr_group, raiseerr, extra_criteria
+    ):
+        return path
+
+    def _prepare_for_compile_state(
+        self,
+        parent_loader,
+        compile_state,
+        mapper_entities,
+        reconciled_lead_entity,
+        raiseerr,
+    ):
+        # _ClassStrategyLoad
+
+        current_path = compile_state.current_path
+        is_refresh = compile_state.compile_options._for_refresh_state
+
+        if is_refresh and not self.propagate_to_loaders:
+            return []
+
+        # omit setting attributes for a "defaultload" type of option
+        if not self.strategy and not self.local_opts:
+            return []
+
+        effective_path = self.path
+
+        if current_path:
+            new_effective_path = self._adjust_effective_path_for_current_path(
+                effective_path, current_path
+            )
+            if new_effective_path is None:
+                return []
+            effective_path = new_effective_path
+
+        return [("loader", effective_path.natural_path)]
+
+
+def _generate_from_keys(
+    meth: Callable[..., _AbstractLoad],
+    keys: Tuple[_AttrType, ...],
+    chained: bool,
+    kw: Any,
+) -> _AbstractLoad:
+    lead_element: Optional[_AbstractLoad] = None
+
+    attr: Any
+    for is_default, _keys in (True, keys[0:-1]), (False, keys[-1:]):
+        for attr in _keys:
+            if isinstance(attr, str):
+                if attr.startswith("." + _WILDCARD_TOKEN):
+                    util.warn_deprecated(
+                        "The undocumented `.{WILDCARD}` format is "
+                        "deprecated "
+                        "and will be removed in a future version as "
+                        "it is "
+                        "believed to be unused. "
+                        "If you have been using this functionality, "
+                        "please "
+                        "comment on Issue #4390 on the SQLAlchemy project "
+                        "tracker.",
+                        version="1.4",
+                    )
+                    attr = attr[1:]
+
+                if attr == _WILDCARD_TOKEN:
+                    if is_default:
+                        raise sa_exc.ArgumentError(
+                            "Wildcard token cannot be followed by "
+                            "another entity",
+                        )
+
+                    if lead_element is None:
+                        lead_element = _WildcardLoad()
+
+                    lead_element = meth(lead_element, _DEFAULT_TOKEN, **kw)
+
+                else:
+                    raise sa_exc.ArgumentError(
+                        "Strings are not accepted for attribute names in "
+                        "loader options; please use class-bound "
+                        "attributes directly.",
+                    )
+            else:
+                if lead_element is None:
+                    _, lead_entity, _ = _parse_attr_argument(attr)
+                    lead_element = Load(lead_entity)
+
+                if is_default:
+                    if not chained:
+                        lead_element = lead_element.defaultload(attr)
+                    else:
+                        lead_element = meth(
+                            lead_element, attr, _is_chain=True, **kw
+                        )
+                else:
+                    lead_element = meth(lead_element, attr, **kw)
+
+    assert lead_element
+    return lead_element
+
+
+def _parse_attr_argument(
+    attr: _AttrType,
+) -> Tuple[InspectionAttr, _InternalEntityType[Any], MapperProperty[Any]]:
+    """parse an attribute or wildcard argument to produce an
+    :class:`._AbstractLoad` instance.
+
+    This is used by the standalone loader strategy functions like
+    ``joinedload()``, ``defer()``, etc. to produce :class:`_orm.Load` or
+    :class:`._WildcardLoad` objects.
+
+    """
+    try:
+        # TODO: need to figure out this None thing being returned by
+        # inspect(), it should not have None as an option in most cases
+        # if at all
+        insp: InspectionAttr = inspect(attr)  # type: ignore
+    except sa_exc.NoInspectionAvailable as err:
+        raise sa_exc.ArgumentError(
+            "expected ORM mapped attribute for loader strategy argument"
+        ) from err
+
+    lead_entity: _InternalEntityType[Any]
+
+    if insp_is_mapper_property(insp):
+        lead_entity = insp.parent
+        prop = insp
+    elif insp_is_attribute(insp):
+        lead_entity = insp.parent
+        prop = insp.prop
+    else:
+        raise sa_exc.ArgumentError(
+            "expected ORM mapped attribute for loader strategy argument"
+        )
+
+    return insp, lead_entity, prop
+
+
+def loader_unbound_fn(fn: _FN) -> _FN:
+    """decorator that applies docstrings between standalone loader functions
+    and the loader methods on :class:`._AbstractLoad`.
+
+    """
+    bound_fn = getattr(_AbstractLoad, fn.__name__)
+    fn_doc = bound_fn.__doc__
+    bound_fn.__doc__ = f"""Produce a new :class:`_orm.Load` object with the
+:func:`_orm.{fn.__name__}` option applied.
+
+See :func:`_orm.{fn.__name__}` for usage examples.
+
+"""
+
+    fn.__doc__ = fn_doc
+    return fn
+
+
+# standalone functions follow.  docstrings are filled in
+# by the ``@loader_unbound_fn`` decorator.
+
+
+@loader_unbound_fn
+def contains_eager(*keys: _AttrType, **kw: Any) -> _AbstractLoad:
+    return _generate_from_keys(Load.contains_eager, keys, True, kw)
+
+
+@loader_unbound_fn
+def load_only(*attrs: _AttrType, raiseload: bool = False) -> _AbstractLoad:
+    # TODO: attrs against different classes.  we likely have to
+    # add some extra state to Load of some kind
+    _, lead_element, _ = _parse_attr_argument(attrs[0])
+    return Load(lead_element).load_only(*attrs, raiseload=raiseload)
+
+
+@loader_unbound_fn
+def joinedload(*keys: _AttrType, **kw: Any) -> _AbstractLoad:
+    return _generate_from_keys(Load.joinedload, keys, False, kw)
+
+
+@loader_unbound_fn
+def subqueryload(*keys: _AttrType) -> _AbstractLoad:
+    return _generate_from_keys(Load.subqueryload, keys, False, {})
+
+
+@loader_unbound_fn
+def selectinload(
+    *keys: _AttrType, recursion_depth: Optional[int] = None
+) -> _AbstractLoad:
+    return _generate_from_keys(
+        Load.selectinload, keys, False, {"recursion_depth": recursion_depth}
+    )
+
+
+@loader_unbound_fn
+def lazyload(*keys: _AttrType) -> _AbstractLoad:
+    return _generate_from_keys(Load.lazyload, keys, False, {})
+
+
+@loader_unbound_fn
+def immediateload(
+    *keys: _AttrType, recursion_depth: Optional[int] = None
+) -> _AbstractLoad:
+    return _generate_from_keys(
+        Load.immediateload, keys, False, {"recursion_depth": recursion_depth}
+    )
+
+
+@loader_unbound_fn
+def noload(*keys: _AttrType) -> _AbstractLoad:
+    return _generate_from_keys(Load.noload, keys, False, {})
+
+
+@loader_unbound_fn
+def raiseload(*keys: _AttrType, **kw: Any) -> _AbstractLoad:
+    return _generate_from_keys(Load.raiseload, keys, False, kw)
+
+
+@loader_unbound_fn
+def defaultload(*keys: _AttrType) -> _AbstractLoad:
+    return _generate_from_keys(Load.defaultload, keys, False, {})
+
+
+@loader_unbound_fn
+def defer(
+    key: _AttrType, *addl_attrs: _AttrType, raiseload: bool = False
+) -> _AbstractLoad:
+    if addl_attrs:
+        util.warn_deprecated(
+            "The *addl_attrs on orm.defer is deprecated.  Please use "
+            "method chaining in conjunction with defaultload() to "
+            "indicate a path.",
+            version="1.3",
+        )
+
+    if raiseload:
+        kw = {"raiseload": raiseload}
+    else:
+        kw = {}
+
+    return _generate_from_keys(Load.defer, (key,) + addl_attrs, False, kw)
+
+
+@loader_unbound_fn
+def undefer(key: _AttrType, *addl_attrs: _AttrType) -> _AbstractLoad:
+    if addl_attrs:
+        util.warn_deprecated(
+            "The *addl_attrs on orm.undefer is deprecated.  Please use "
+            "method chaining in conjunction with defaultload() to "
+            "indicate a path.",
+            version="1.3",
+        )
+    return _generate_from_keys(Load.undefer, (key,) + addl_attrs, False, {})
+
+
+@loader_unbound_fn
+def undefer_group(name: str) -> _AbstractLoad:
+    element = _WildcardLoad()
+    return element.undefer_group(name)
+
+
+@loader_unbound_fn
+def with_expression(
+    key: _AttrType, expression: _ColumnExpressionArgument[Any]
+) -> _AbstractLoad:
+    return _generate_from_keys(
+        Load.with_expression, (key,), False, {"expression": expression}
+    )
+
+
+@loader_unbound_fn
+def selectin_polymorphic(
+    base_cls: _EntityType[Any], classes: Iterable[Type[Any]]
+) -> _AbstractLoad:
+    ul = Load(base_cls)
+    return ul.selectin_polymorphic(classes)
+
+
+def _raise_for_does_not_link(path, attrname, parent_entity):
+    if len(path) > 1:
+        path_is_of_type = path[-1].entity is not path[-2].mapper.class_
+        if insp_is_aliased_class(parent_entity):
+            parent_entity_str = str(parent_entity)
+        else:
+            parent_entity_str = parent_entity.class_.__name__
+
+        raise sa_exc.ArgumentError(
+            f'ORM mapped entity or attribute "{attrname}" does not '
+            f'link from relationship "{path[-2]}%s".%s'
+            % (
+                f".of_type({path[-1]})" if path_is_of_type else "",
+                (
+                    "  Did you mean to use "
+                    f'"{path[-2]}'
+                    f'.of_type({parent_entity_str})" or "loadopt.options('
+                    f"selectin_polymorphic({path[-2].mapper.class_.__name__}, "
+                    f'[{parent_entity_str}]), ...)" ?'
+                    if not path_is_of_type
+                    and not path[-1].is_aliased_class
+                    and orm_util._entity_corresponds_to(
+                        path.entity, inspect(parent_entity).mapper
+                    )
+                    else ""
+                ),
+            )
+        )
+    else:
+        raise sa_exc.ArgumentError(
+            f'ORM mapped attribute "{attrname}" does not '
+            f'link mapped class "{path[-1]}"'
+        )