Merge "More efficient db resources-per-stack count"

heat/db/sqlalchemy/api.py

@@ -741,10 +741,9 @@ def stack_get_root_id(context, stack_id):
 
 def stack_count_total_resources(context, stack_id):
     # count all resources which belong to the root stack
-    results = context.session.query(
-        models.Resource
-    ).filter(models.Resource.root_stack_id == stack_id).count()
-    return results
+    return context.session.query(
+        func.count(models.Resource.id)
+    ).filter_by(root_stack_id=stack_id).scalar()
 
 
 def user_creds_create(context):