resolve synonyms in dictionary form of Session.get()

Improved "dictionary mode" for :meth:`_orm.Session.get` so that synonym
names which refer to primary key attribute names may be indicated in the
named dictionary.

Fixes: #8753
Change-Id: I56112564a5c23b51b26e01c64087cbf4399cd951

2 files changed, 34 insertions, 1 deletions

diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py
index 890728738..5f7ff43e4 100644
--- a/lib/sqlalchemy/orm/mapper.py
+++ b/lib/sqlalchemy/orm/mapper.py
@@ -2910,6 +2910,24 @@ class Mapper(
 
     @HasMemoized.memoized_attribute
     @util.preload_module("sqlalchemy.orm.descriptor_props")
+    def _pk_synonyms(self) -> Dict[str, str]:
+        """return a dictionary of {syn_attribute_name: pk_attr_name} for
+        all synonyms that refer to primary key columns
+
+        """
+        descriptor_props = util.preloaded.orm_descriptor_props
+
+        pk_keys = {prop.key for prop in self._identity_key_props}
+
+        return {
+            syn.key: syn.name
+            for k, syn in self._props.items()
+            if isinstance(syn, descriptor_props.SynonymProperty)
+            and syn.name in pk_keys
+        }
+
+    @HasMemoized.memoized_attribute
+    @util.preload_module("sqlalchemy.orm.descriptor_props")
     def synonyms(self) -> util.ReadOnlyProperties[SynonymProperty[Any]]:
         """Return a namespace of all :class:`.Synonym`
         properties maintained by this :class:`_orm.Mapper`.
diff --git a/lib/sqlalchemy/orm/session.py b/lib/sqlalchemy/orm/session.py
index 540e64e7d..849d37ab2 100644
--- a/lib/sqlalchemy/orm/session.py
+++ b/lib/sqlalchemy/orm/session.py
@@ -3399,6 +3399,21 @@ class Session(_SessionClassMethods, EventTarget):
             )
 
         if is_dict:
+
+            pk_synonyms = mapper._pk_synonyms
+
+            if pk_synonyms:
+                correct_keys = set(pk_synonyms).intersection(
+                    primary_key_identity
+                )
+
+                if correct_keys:
+                    primary_key_identity = dict(primary_key_identity)
+                    for k in correct_keys:
+                        primary_key_identity[
+                            pk_synonyms[k]
+                        ] = primary_key_identity[k]
+
             try:
                 primary_key_identity = list(
                     primary_key_identity[prop.key]
@@ -3409,7 +3424,7 @@ class Session(_SessionClassMethods, EventTarget):
                 raise sa_exc.InvalidRequestError(
                     "Incorrect names of values in identifier to formulate "
                     "primary key for session.get(); primary key attribute "
-                    "names are %s"
+                    "names are %s (synonym names are also accepted)"
                     % ",".join(
                         "'%s'" % prop.key
                         for prop in mapper._identity_key_props