Added a new exception to detect the case where two

subclasses are being loaded using with_polymorphic(),
each subclass contains a relationship attribute of the same
name, and eager loading is being applied to one or both.
This is an ongoing bug which can't be immediately fixed,
so since the results are usually wrong in any case it raises an
exception for now.   0.7 has the same issue, so an exception
raise here probably means the code was returning the wrong
data in 0.7.  [ticket:2614]

2 files changed, 23 insertions, 2 deletions

diff --git a/lib/sqlalchemy/orm/strategies.py b/lib/sqlalchemy/orm/strategies.py
index 39329f9b1..586ec4b4e 100644
--- a/lib/sqlalchemy/orm/strategies.py
+++ b/lib/sqlalchemy/orm/strategies.py
@@ -303,6 +303,17 @@ class AbstractRelationshipLoader(LoaderStrategy):
         self.uselist = self.parent_property.uselist
 
 
+    def _warn_existing_path(self):
+        raise sa_exc.InvalidRequestError(
+            "Eager loading cannot currently function correctly when two or "
+            "more "
+            "same-named attributes associated with multiple polymorphic "
+            "classes "
+            "of the same base are present.   Encountered more than one "
+            r"eager path for attribute '%s' on mapper '%s'." %
+            (self.key, self.parent.base_mapper, ))
+
+
 class NoLoader(AbstractRelationshipLoader):
     """Provide loading behavior for a :class:`.RelationshipProperty`
     with "lazy=None".
@@ -746,7 +757,9 @@ class SubqueryLoader(AbstractRelationshipLoader):
 
         # add new query to attributes to be picked up
         # by create_row_processor
-        path.set(context, "subquery", q)
+        existing = path.replace(context, "subquery", q)
+        if existing:
+            self._warn_existing_path()
 
     def _get_leftmost(self, subq_path):
         subq_path = subq_path.path
@@ -1091,7 +1104,9 @@ class JoinedLoader(AbstractRelationshipLoader):
         )
 
         add_to_collection = context.secondary_columns
-        path.set(context, "eager_row_processor", clauses)
+        existing = path.replace(context, "eager_row_processor", clauses)
+        if existing:
+            self._warn_existing_path()
         return clauses, adapter, add_to_collection, allow_innerjoin
 
     def _create_eager_join(self, context, entity,
diff --git a/lib/sqlalchemy/orm/util.py b/lib/sqlalchemy/orm/util.py
index 97baffc9a..e5e725138 100644
--- a/lib/sqlalchemy/orm/util.py
+++ b/lib/sqlalchemy/orm/util.py
@@ -279,6 +279,12 @@ class PathRegistry(object):
     def set(self, reg, key, value):
         reg._attributes[(key, self.reduced_path)] = value
 
+    def replace(self, reg, key, value):
+        path_key = (key, self.reduced_path)
+        existing = reg._attributes.get(path_key, None)
+        reg._attributes[path_key] = value
+        return existing
+
     def setdefault(self, reg, key, value):
         reg._attributes.setdefault((key, self.reduced_path), value)