Cache polymorphic_iterator in UOWTask; substantial savings for polymorphism-heavy workloads.

2 files changed, 18 insertions, 1 deletions

diff --git a/lib/sqlalchemy/orm/unitofwork.py b/lib/sqlalchemy/orm/unitofwork.py
index 8412887a4..52bf1578e 100644
--- a/lib/sqlalchemy/orm/unitofwork.py
+++ b/lib/sqlalchemy/orm/unitofwork.py
@@ -342,6 +342,10 @@ class UOWTask(object):
         self.dependencies = set()
         self.cyclical_dependencies = set()
 
+    @util.lazy_property
+    def inheriting_mappers(self):
+        return list(self.mapper.polymorphic_iterator())
+
     @property
     def polymorphic_tasks(self):
         """Return an iterator of UOWTask objects corresponding to the
@@ -372,7 +376,7 @@ class UOWTask(object):
         those mappers.
 
         """
-        for mapper in self.mapper.polymorphic_iterator():
+        for mapper in self.inheriting_mappers:
             t = self.base_task._inheriting_tasks.get(mapper, None)
             if t is not None:
                 yield t
diff --git a/lib/sqlalchemy/util.py b/lib/sqlalchemy/util.py
index 88245945e..770b48796 100644
--- a/lib/sqlalchemy/util.py
+++ b/lib/sqlalchemy/util.py
@@ -395,6 +395,19 @@ def iterate_attributes(cls):
                 yield (key, c.__dict__[key])
                 break
 
+class lazy_property(object):
+    """A read-only @property that is only evaluated once."""
+    def __init__(self, fget, doc=None):
+        self.fget = fget
+        self.__doc__ = doc or fget.__doc__
+        self.__name__ = fget.__name__
+
+    def __get__(self, obj, cls):
+        if obj is None:
+            return None
+        obj.__dict__[self.__name__] = result = self.fget(obj)
+        return result
+
 # from paste.deploy.converters
 def asbool(obj):
     if isinstance(obj, (str, unicode)):