Ticket #10929: 10929-aggregates-default-r17029.diff

tests/modeltests/aggregation/tests.py

@@ -565 +565 @@
                 (Decimal('82.8'), 1),
             ]
         )
+
+    def test_default(self):
+        p = Publisher.objects.create(name='publisher', num_awards=0)
+        # return None if there's no default and no data to aggregate.
+        publisher = Publisher.objects.annotate(avg_book_rating=Avg("book__rating")).get(pk=p.pk)
+        self.assertEqual(publisher.avg_book_rating, None)
+        # return the default if one is specified and no data to aggregate.
+        publisher = Publisher.objects.annotate(avg_book_rating=Avg("book__rating", 0)).get(pk=p.pk)
+        self.assertEqual(publisher.avg_book_rating, 0.0)

django/db/models/sql/aggregates.py

@@ -89 +89 @@
         }
         params.update(self.extra)
 
-        return self.sql_template % params
+        template = self.sql_template
+        if 'default' in params:
+            template = 'COALESCE(%s, %%(default)s)' % template
 
+        return template % params
 
+
 class Avg(Aggregate):
     is_computed = True
     sql_function = 'AVG'

django/db/models/aggregates.py

@@ -6 +6 @@
     """
     Default Aggregate definition.
     """
-    def __init__(self, lookup, **extra):
+    def __init__(self, lookup, default=None, **extra):
         """Instantiate a new aggregate.
 
          * lookup is the field on which the aggregate operates.
@@ -16 +16 @@
         Also utilizes the class variables:
          * name, the identifier for this aggregate function.
         """
+        if default is not None:
+            extra.setdefault('default', default)
         self.lookup = lookup
         self.extra = extra