gh-62.patch

=== modified file 'mptt/managers.py'
--- mptt/managers.py	2008-12-05 01:37:34 +0000
+++ mptt/managers.py	2008-12-05 19:08:24 +0000
@@ -11,15 +11,11 @@
 qn = connection.ops.quote_name
 
 COUNT_SUBQUERY = """(
-    SELECT COUNT(*)
-    FROM %(rel_table)s
-    WHERE %(mptt_fk)s = %(mptt_table)s.%(mptt_pk)s
+    %(mptt_fk)s = %(mptt_table)s.%(mptt_pk)s
 )"""
 
 CUMULATIVE_COUNT_SUBQUERY = """(
-    SELECT COUNT(*)
-    FROM %(rel_table)s
-    WHERE %(mptt_fk)s IN
+    %(mptt_fk)s IN
     (
         SELECT m2.%(mptt_pk)s
         FROM %(mptt_table)s m2
@@ -29,6 +25,7 @@
     )
 )"""
 
+
 class TreeManager(models.Manager):
     """
     A manager for working with trees of objects.
@@ -47,7 +44,7 @@
         self.tree_id_attr = tree_id_attr
         self.level_attr = level_attr
 
-    def add_related_count(self, queryset, rel_model, rel_field, count_attr,
+    def add_related_count(self, queryset, rel_queryset, rel_field, count_attr,
                           cumulative=False):
         """
         Adds a related item count to a given ``QuerySet`` using its
@@ -56,9 +53,8 @@
 
         Arguments:
 
-        ``rel_model``
-           A ``Model`` class which has a relation to this `Manager``'s
-           ``Model`` class.
+        ``rel_queryset``
+           A ``QuerySet`` class for related model.
 
         ``rel_field``
            The name of the field in ``rel_model`` which holds the
@@ -74,24 +70,24 @@
            descendants, otherwise it will be for each item itself.
         """
         opts = self.model._meta
+        rel_model = rel_queryset.model
         if cumulative:
-            subquery = CUMULATIVE_COUNT_SUBQUERY % {
-                'rel_table': qn(rel_model._meta.db_table),
+            rel_queryset = rel_queryset.extra(where=[CUMULATIVE_COUNT_SUBQUERY % {
                 'mptt_fk': qn(rel_model._meta.get_field(rel_field).column),
                 'mptt_table': qn(opts.db_table),
                 'mptt_pk': qn(opts.pk.column),
                 'tree_id': qn(opts.get_field(self.tree_id_attr).column),
                 'left': qn(opts.get_field(self.left_attr).column),
                 'right': qn(opts.get_field(self.right_attr).column),
-            }
+            }])
         else:
-            subquery = COUNT_SUBQUERY % {
-                'rel_table': qn(rel_model._meta.db_table),
+            rel_queryset = rel_queryset.extra(where=[COUNT_SUBQUERY % {
                 'mptt_fk': qn(rel_model._meta.get_field(rel_field).column),
                 'mptt_table': qn(opts.db_table),
                 'mptt_pk': qn(opts.pk.column),
-            }
-        return queryset.extra(select={count_attr: subquery})
+            }])
+        rel_queryset.query.add_count_column()
+        return queryset.extra(select={count_attr: rel_queryset.query})
 
     def get_query_set(self):
         """