queryset-refactor: Added caching for reverse-one-to-one lookups.

This is the only type of reverse lookup where caching makes sense might make
some kinds of model inheritance interactions more database friendly.


git-svn-id: http://code.djangoproject.com/svn/django/branches/queryset-refactor@7171 bcc190cf-cafb-0310-a4f2-bffc1f526a37

1 files changed, 8 insertions, 3 deletions

diff --git a/django/db/models/fields/related.py b/django/db/models/fields/related.py
index f6594d617a..20b35cc3d8 100644
--- a/django/db/models/fields/related.py
+++ b/django/db/models/fields/related.py
@@ -125,14 +125,19 @@ class SingleRelatedObjectDescriptor(object):
     # SingleRelatedObjectDescriptor instance.
     def __init__(self, related):
         self.related = related
+        self.cache_name = '_%s_cache' % related.field.name
 
     def __get__(self, instance, instance_type=None):
         if instance is None:
             raise AttributeError, "%s must be accessed via instance" % self.related.opts.object_name
 
-        params = {'%s__pk' % self.related.field.name: instance._get_pk_val()}
-        rel_obj = self.related.model._default_manager.get(**params)
-        return rel_obj
+        try:
+            return getattr(instance, self.cache_name)
+        except AttributeError:
+            params = {'%s__pk' % self.related.field.name: instance._get_pk_val()}
+            rel_obj = self.related.model._default_manager.get(**params)
+            setattr(instance, self.cache_name, rel_obj)
+            return rel_obj
 
     def __set__(self, instance, value):
         if instance is None: