From 4276b5197b2acc2c15ef719b1f1308c41f704725 Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Wed, 17 Nov 2010 02:57:14 +0000
Subject: [PATCH] Fixed #12687 -- fixed an issue with aggregates and counts in
 conjunction with annotations where the QuerySet was provably empty.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14586 bcc190cf-cafb-0310-a4f2-bffc1f526a37
---
 django/db/models/sql/aggregates.py            |  1 +
 django/db/models/sql/query.py                 | 20 +++++++++++++++----
 django/db/models/sql/subqueries.py            |  1 +
 .../aggregation_regress/tests.py              | 18 +++++++++++++++++
 4 files changed, 36 insertions(+), 4 deletions(-)

diff --git a/django/db/models/sql/aggregates.py b/django/db/models/sql/aggregates.py
index 8a14bdf2df..207bc0c6c8 100644
--- a/django/db/models/sql/aggregates.py
+++ b/django/db/models/sql/aggregates.py
@@ -8,6 +8,7 @@ class AggregateField(object):
     """
     def __init__(self, internal_type):
         self.internal_type = internal_type
+
     def get_internal_type(self):
         return self.internal_type
 
diff --git a/django/db/models/sql/query.py b/django/db/models/sql/query.py
index ec477447f3..c0449e7047 100644
--- a/django/db/models/sql/query.py
+++ b/django/db/models/sql/query.py
@@ -337,7 +337,7 @@ class Query(object):
         # information but retrieves only the first row. Aggregate
         # over the subquery instead.
         if self.group_by is not None:
-            from subqueries import AggregateQuery
+            from django.db.models.sql.subqueries import AggregateQuery
             query = AggregateQuery(self.model)
 
             obj = self.clone()
@@ -349,7 +349,13 @@ class Query(object):
                     query.aggregate_select[alias] = aggregate
                     del obj.aggregate_select[alias]
 
-            query.add_subquery(obj, using)
+            try:
+                query.add_subquery(obj, using)
+            except EmptyResultSet:
+                return dict(
+                    (alias, None)
+                    for alias in query.aggregate_select
+                )
         else:
             query = self
             self.select = []
@@ -382,13 +388,19 @@ class Query(object):
             # If a select clause exists, then the query has already started to
             # specify the columns that are to be returned.
             # In this case, we need to use a subquery to evaluate the count.
-            from subqueries import AggregateQuery
+            from django.db.models.sql.subqueries import AggregateQuery
             subquery = obj
             subquery.clear_ordering(True)
             subquery.clear_limits()
 
             obj = AggregateQuery(obj.model)
-            obj.add_subquery(subquery, using=using)
+            try:
+                obj.add_subquery(subquery, using=using)
+            except EmptyResultSet:
+                # add_subquery evaluates the query, if it's an EmptyResultSet
+                # then there are can be no results, and therefore there the
+                # count is obviously 0
+                return 0
 
         obj.add_count_column()
         number = obj.get_aggregation(using=using)[None]
diff --git a/django/db/models/sql/subqueries.py b/django/db/models/sql/subqueries.py
index a62adfe0fc..003bf432c0 100644
--- a/django/db/models/sql/subqueries.py
+++ b/django/db/models/sql/subqueries.py
@@ -11,6 +11,7 @@ from django.db.models.sql.expressions import SQLEvaluator
 from django.db.models.sql.query import Query
 from django.db.models.sql.where import AND, Constraint
 
+
 __all__ = ['DeleteQuery', 'UpdateQuery', 'InsertQuery', 'DateQuery',
         'AggregateQuery']
 
diff --git a/tests/regressiontests/aggregation_regress/tests.py b/tests/regressiontests/aggregation_regress/tests.py
index c82fd996fd..813cc4839d 100644
--- a/tests/regressiontests/aggregation_regress/tests.py
+++ b/tests/regressiontests/aggregation_regress/tests.py
@@ -622,6 +622,24 @@ class AggregationTests(TestCase):
             lambda: Book.objects.annotate(mean_age=Avg('authors__age')).annotate(Avg('mean_age'))
         )
 
+    def test_empty_filter_count(self):
+        self.assertEqual(
+            Author.objects.filter(id__in=[]).annotate(Count("friends")).count(),
+            0
+        )
+
+    def test_empty_filter_aggregate(self):
+        self.assertEqual(
+            Author.objects.filter(id__in=[]).annotate(Count("friends")).aggregate(Count("pk")),
+            {"pk__count": None}
+        )
+
+    def test_annotate_and_join(self):
+        self.assertEqual(
+            Author.objects.annotate(c=Count("friends__name")).exclude(friends__name="Joe").count(),
+            Author.objects.count()
+        )
+
     @skipUnlessDBFeature('supports_stddev')
     def test_stddev(self):
         self.assertEqual(