Fixed #10089 -- Corrected handling of aggregates when the query set contains no items (and the cursor returns None). Thanks to Kyle Fox for the report, and david for the initial patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@9786 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/sql/query.py

@@ -217,6 +217,8 @@ class BaseQuery(object):
         to return Decimal and long types when they are not needed.
         """
         if value is None:
+            if aggregate.is_ordinal:
+                return 0
             # Return None as-is
             return value
         elif aggregate.is_ordinal:
@@ -295,10 +297,14 @@ class BaseQuery(object):
         query.related_select_cols = []
         query.related_select_fields = []
 
+        result = query.execute_sql(SINGLE)
+        if result is None:
+            result = [None for q in query.aggregate_select.items()]
+
         return dict([
             (alias, self.resolve_aggregate(val, aggregate))
             for (alias, aggregate), val
-            in zip(query.aggregate_select.items(), query.execute_sql(SINGLE))
+            in zip(query.aggregate_select.items(), result)
         ])
 
     def get_count(self):

tests/modeltests/aggregation/fixtures/initial_data.json

@@ -31,6 +31,14 @@
             "num_awards": 9
         }
     },
+    {
+        "pk": 5,
+        "model": "aggregation.publisher",
+        "fields": {
+            "name": "Jonno's House of Books",
+            "num_awards": 0
+        }
+    },
     {
         "pk": 1,
         "model": "aggregation.book",

tests/modeltests/aggregation/models.py

@@ -194,7 +194,7 @@ u'The Definitive Guide to Django: Web Development Done Right'
 # Annotate each publisher with the sum of the price of all books sold
 >>> publishers = Publisher.objects.all().annotate(Sum('book__price'))
 >>> sorted([(p.name, p.book__price__sum) for p in publishers])
-[(u'Apress', Decimal("59.69")), (u'Morgan Kaufmann', Decimal("75.00")), (u'Prentice Hall', Decimal("112.49")), (u'Sams', Decimal("23.09"))]
+[(u'Apress', Decimal("59.69")), (u"Jonno's House of Books", None), (u'Morgan Kaufmann', Decimal("75.00")), (u'Prentice Hall', Decimal("112.49")), (u'Sams', Decimal("23.09"))]
 
 # Calls to values() are not commutative over annotate().
 
@@ -356,7 +356,7 @@ True
 []
 
 # Aggregates also work on dates, times and datetimes
->>> Publisher.objects.annotate(earliest_book=Min('book__pubdate')).order_by('earliest_book').values()
+>>> Publisher.objects.annotate(earliest_book=Min('book__pubdate')).exclude(earliest_book=None).order_by('earliest_book').values()
 [{'earliest_book': datetime.date(1991, 10, 15), 'num_awards': 9, 'id': 4, 'name': u'Morgan Kaufmann'}, {'earliest_book': datetime.date(1995, 1, 15), 'num_awards': 7, 'id': 3, 'name': u'Prentice Hall'}, {'earliest_book': datetime.date(2007, 12, 6), 'num_awards': 3, 'id': 1, 'name': u'Apress'}, {'earliest_book': datetime.date(2008, 3, 3), 'num_awards': 1, 'id': 2, 'name': u'Sams'}]
 
 >>> Store.objects.aggregate(Max('friday_night_closing'), Min("original_opening"))

tests/regressiontests/aggregation_regress/fixtures/initial_data.json

@@ -31,6 +31,14 @@
             "num_awards": 9
         }
     },
+    {
+        "pk": 5,
+        "model": "aggregation_regress.publisher",
+        "fields": {
+            "name": "Jonno's House of Books",
+            "num_awards": 0
+        }
+    },
     {
         "pk": 1,
         "model": "aggregation_regress.book",

tests/regressiontests/aggregation_regress/models.py

@@ -164,6 +164,16 @@ FieldError: Cannot resolve keyword 'foo' into field. Choices are: authors, id, i
 >>> len(Book.objects.annotate(num_authors=Count('authors')).exclude(num_authors__lt=2).filter(num_authors__lt=3))
 2
 
+# Regression for #10089: Check handling of empty result sets with aggregates
+>>> Book.objects.filter(id__in=[]).count()
+0
+
+>>> Book.objects.filter(id__in=[]).aggregate(num_authors=Count('authors'), avg_authors=Avg('authors'), max_authors=Max('authors'), max_price=Max('price'), max_rating=Max('rating'))
+{'max_authors': None, 'max_rating': None, 'num_authors': 0, 'avg_authors': None, 'max_price': None}
+
+>>> Publisher.objects.filter(pk=5).annotate(num_authors=Count('book__authors'), avg_authors=Avg('book__authors'), max_authors=Max('book__authors'), max_price=Max('book__price'), max_rating=Max('book__rating')).values()
+[{'max_authors': None, 'name': u"Jonno's House of Books", 'num_awards': 0, 'max_price': None, 'num_authors': 0, 'max_rating': None, 'id': 5, 'avg_authors': None}]
+
 """
 }