Raise for unexpected polymorphic identity

A query that is against an mapped inheritance subclass which also uses
:meth:`.Query.select_entity_from` or a similar technique in order  to
provide an existing subquery to SELECT from, will now raise an error if the
given subquery returns entities that do not correspond to the given
subclass, that is, they are sibling or superclasses in the same hierarchy.
Previously, these would be returned without error.  Additionally, if the
inheritance mapping is a single-inheritance mapping, the given subquery
must apply the appropriate filtering against the polymorphic discriminator
column in order to avoid this error; previously, the :class:`.Query` would
add this criteria to the outside query however this interferes with some
kinds of query that return other kinds of entities as well.

Fixes: #5122
Change-Id: I60cf8c1300d5bb279ad99f0f01fefe7e008a159b

1 files changed, 4 insertions, 4 deletions

diff --git a/lib/sqlalchemy/orm/query.py b/lib/sqlalchemy/orm/query.py
index 55b569bcd..15319e049 100644
--- a/lib/sqlalchemy/orm/query.py
+++ b/lib/sqlalchemy/orm/query.py
@@ -260,6 +260,7 @@ class Query(Generative):
             self._from_obj_alias = sql_util.ColumnAdapter(
                 self._from_obj[0], equivs
             )
+            self._enable_single_crit = False
         elif (
             set_base_alias
             and len(self._from_obj) == 1
@@ -267,6 +268,7 @@ class Query(Generative):
             and info.is_aliased_class
         ):
             self._from_obj_alias = info._adapter
+            self._enable_single_crit = False
 
     def _reset_polymorphic_adapter(self, mapper):
         for m2 in mapper._with_polymorphic_mappers:
@@ -1379,7 +1381,6 @@ class Query(Generative):
             ._anonymous_fromclause()
         )
         q = self._from_selectable(fromclause)
-        q._enable_single_crit = False
         q._select_from_entity = self._entity_zero()
         if entities:
             q._set_entities(entities)
@@ -1407,6 +1408,7 @@ class Query(Generative):
         ):
             self.__dict__.pop(attr, None)
         self._set_select_from([fromclause], True)
+        self._enable_single_crit = False
 
         # this enables clause adaptation for non-ORM
         # expressions.
@@ -1875,9 +1877,7 @@ class Query(Generative):
             self._having = criterion
 
     def _set_op(self, expr_fn, *q):
-        return self._from_selectable(
-            expr_fn(*([self] + list(q))).subquery()
-        )._set_enable_single_crit(False)
+        return self._from_selectable(expr_fn(*([self] + list(q))).subquery())
 
     def union(self, *q):
         """Produce a UNION of this Query against one or more queries.