selectin polymorphic loading

Added a new style of mapper-level inheritance loading
"polymorphic selectin".  This style of loading
emits queries for each subclass in an inheritance
hierarchy subsequent to the load of the base
object type, using IN to specify the desired
primary key values.

Fixes: #3948

Change-Id: I59e071c6142354a3f95730046e3dcdfc0e2c4de5

1 files changed, 21 insertions, 0 deletions

diff --git a/lib/sqlalchemy/orm/util.py b/lib/sqlalchemy/orm/util.py
index 9a397ccf3..4267b79fb 100644
--- a/lib/sqlalchemy/orm/util.py
+++ b/lib/sqlalchemy/orm/util.py
@@ -1043,7 +1043,13 @@ def was_deleted(object):
     state = attributes.instance_state(object)
     return state.was_deleted
 
+
 def _entity_corresponds_to(given, entity):
+    """determine if 'given' corresponds to 'entity', in terms
+    of an entity passed to Query that would match the same entity
+    being referred to elsewhere in the query.
+
+    """
     if entity.is_aliased_class:
         if given.is_aliased_class:
             if entity._base_alias is given._base_alias:
@@ -1057,6 +1063,21 @@ def _entity_corresponds_to(given, entity):
 
     return entity.common_parent(given)
 
+
+def _entity_isa(given, mapper):
+    """determine if 'given' "is a" mapper, in terms of the given
+    would load rows of type 'mapper'.
+
+    """
+    if given.is_aliased_class:
+        return mapper in given.with_polymorphic_mappers or \
+            given.mapper.isa(mapper)
+    elif given.with_polymorphic_mappers:
+        return mapper in given.with_polymorphic_mappers
+    else:
+        return given.isa(mapper)
+
+
 def randomize_unitofwork():
     """Use random-ordering sets within the unit of work in order
     to detect unit of work sorting issues.