- [feature] *Very limited* support for

    inheriting mappers to be GC'ed when the
    class itself is deferenced.  The mapper
    must not have its own table (i.e.
    single table inh only) without polymorphic
    attributes in place.
    This allows for the use case of
    creating a temporary subclass of a declarative
    mapped class, with no table or mapping
    directives of its own, to be garbage collected
    when dereferenced by a unit test.
    [ticket:2526]

1 files changed, 7 insertions, 6 deletions

diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py
index 76d6b1165..57c8de498 100644
--- a/lib/sqlalchemy/orm/mapper.py
+++ b/lib/sqlalchemy/orm/mapper.py
@@ -431,7 +431,7 @@ class Mapper(object):
         being present."""
 
         # a set of all mappers which inherit from this one.
-        self._inheriting_mappers = set()
+        self._inheriting_mappers = util.WeakSet()
 
         if self.inherits:
             if isinstance(self.inherits, type):
@@ -1308,7 +1308,6 @@ class Mapper(object):
             tables = set(sql_util.find_tables(selectable,
                             include_aliases=True))
             mappers = [m for m in mappers if m.local_table in tables]
-
         return mappers
 
     def _selectable_from_mappers(self, mappers, innerjoin):
@@ -1383,7 +1382,7 @@ class Mapper(object):
 
     @_memoized_configured_property
     def _polymorphic_properties(self):
-        return tuple(self._iterate_polymorphic_properties(
+        return list(self._iterate_polymorphic_properties(
             self._with_polymorphic_mappers))
 
     def _iterate_polymorphic_properties(self, mappers=None):
@@ -1401,8 +1400,10 @@ class Mapper(object):
             # from other mappers, as these are sometimes dependent on that
             # mapper's polymorphic selectable (which we don't want rendered)
             for c in util.unique_list(
-                chain(*[list(mapper.iterate_properties) for mapper in [self] +
-                        mappers])
+                chain(*[
+                        list(mapper.iterate_properties) for mapper in
+                        [self] + mappers
+                    ])
             ):
                 if getattr(c, '_is_polymorphic_discriminator', False) and \
                         (self.polymorphic_on is None or
@@ -1587,7 +1588,7 @@ class Mapper(object):
             item = stack.popleft()
             descendants.append(item)
             stack.extend(item._inheriting_mappers)
-        return tuple(descendants)
+        return util.WeakSequence(descendants)
 
     def polymorphic_iterator(self):
         """Iterate through the collection including this mapper and