Fixed #3566 -- Added support for aggregation to the ORM. See the documentation for details on usage.

Many thanks to:
 * Nicolas Lara, who worked on this feature during the 2008 Google Summer of Code.
 * Alex Gaynor for his help debugging and fixing a number of issues.
 * Justin Bronn for his help integrating with contrib.gis.
 * Karen Tracey for her help with cross-platform testing.
 * Ian Kelly for his help testing and fixing Oracle support.
 * Malcolm Tredinnick for his invaluable review notes.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@9742 bcc190cf-cafb-0310-a4f2-bffc1f526a37

1 files changed, 20 insertions, 10 deletions

diff --git a/django/db/models/sql/subqueries.py b/django/db/models/sql/subqueries.py
index 524b0894c5..0a59b403c8 100644
--- a/django/db/models/sql/subqueries.py
+++ b/django/db/models/sql/subqueries.py
@@ -9,7 +9,7 @@ from django.db.models.sql.query import Query
 from django.db.models.sql.where import AND, Constraint
 
 __all__ = ['DeleteQuery', 'UpdateQuery', 'InsertQuery', 'DateQuery',
-        'CountQuery']
+        'AggregateQuery']
 
 class DeleteQuery(Query):
     """
@@ -400,15 +400,25 @@ class DateQuery(Query):
         self.distinct = True
         self.order_by = order == 'ASC' and [1] or [-1]
 
-class CountQuery(Query):
+class AggregateQuery(Query):
     """
-    A CountQuery knows how to take a normal query which would select over
-    multiple distinct columns and turn it into SQL that can be used on a
-    variety of backends (it requires a select in the FROM clause).
+    An AggregateQuery takes another query as a parameter to the FROM
+    clause and only selects the elements in the provided list.
     """
-    def get_from_clause(self):
-        result, params = self._query.as_sql()
-        return ['(%s) A1' % result], params
+    def add_subquery(self, query):
+        self.subquery, self.sub_params = query.as_sql(with_col_aliases=True)
 
-    def get_ordering(self):
-        return ()
+    def as_sql(self, quote_func=None):
+        """
+        Creates the SQL for this query. Returns the SQL string and list of
+        parameters.
+        """
+        sql = ('SELECT %s FROM (%s) subquery' % (
+            ', '.join([
+                aggregate.as_sql()
+                for aggregate in self.aggregate_select.values()
+            ]),
+            self.subquery)
+        )
+        params = self.sub_params
+        return (sql, params)