suppport with_loader_criteria pickling w/ fixed callable

Fixed issue where a :func:`_orm.with_loader_criteria` option could not be
pickled, as is necessary when it is carried along for propagation to lazy
loaders in conjunction with a caching scheme. Currently, the only form that
is supported as picklable is to pass the "where criteria" as a fixed
module-level callable function that produces a SQL expression. An ad-hoc
"lambda" can't be pickled, and a SQL expression object is usually not fully
picklable directly.

Fixes: #8109
Change-Id: I49fe69088b0c7e58a0f22c67d2ea4e33752a5a73

1 files changed, 28 insertions, 0 deletions

diff --git a/lib/sqlalchemy/orm/util.py b/lib/sqlalchemy/orm/util.py
index e1e78c99d..14a6bccb0 100644
--- a/lib/sqlalchemy/orm/util.py
+++ b/lib/sqlalchemy/orm/util.py
@@ -1138,6 +1138,8 @@ class _WrapUserEntity:
 
     """
 
+    __slots__ = ("subject",)
+
     def __init__(self, subject):
         self.subject = subject
 
@@ -1171,6 +1173,7 @@ class LoaderCriteriaOption(CriteriaOption):
         "entity",
         "deferred_where_criteria",
         "where_criteria",
+        "_where_crit_orig",
         "include_aliases",
         "propagate_to_loaders",
     )
@@ -1190,6 +1193,8 @@ class LoaderCriteriaOption(CriteriaOption):
     include_aliases: bool
     propagate_to_loaders: bool
 
+    _where_crit_orig: Any
+
     def __init__(
         self,
         entity_or_base: _EntityType[Any],
@@ -1210,6 +1215,7 @@ class LoaderCriteriaOption(CriteriaOption):
             self.root_entity = None
             self.entity = entity
 
+        self._where_crit_orig = where_criteria
         if callable(where_criteria):
             if self.root_entity is not None:
                 wrap_entity = self.root_entity
@@ -1235,6 +1241,28 @@ class LoaderCriteriaOption(CriteriaOption):
         self.include_aliases = include_aliases
         self.propagate_to_loaders = propagate_to_loaders
 
+    @classmethod
+    def _unreduce(
+        cls, entity, where_criteria, include_aliases, propagate_to_loaders
+    ):
+        return LoaderCriteriaOption(
+            entity,
+            where_criteria,
+            include_aliases=include_aliases,
+            propagate_to_loaders=propagate_to_loaders,
+        )
+
+    def __reduce__(self):
+        return (
+            LoaderCriteriaOption._unreduce,
+            (
+                self.entity.class_ if self.entity else None,
+                self._where_crit_orig,
+                self.include_aliases,
+                self.propagate_to_loaders,
+            ),
+        )
+
     def _all_mappers(self) -> Iterator[Mapper[Any]]:
 
         if self.entity: