From ddb9b7d57a1da6b8715a62376cbb8605e6b2351b Mon Sep 17 00:00:00 2001
From: Russell Keith-Magee <russell@keith-magee.com>
Date: Thu, 4 Jan 2007 04:00:16 +0000
Subject: [PATCH] Fixed #2473 -- Added special case for '__in=[]' (empty set)
 queries, because 'WHERE attr IN ()' is invalid SQL on many backends. Thanks,
 Gary Wilson.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@4283 bcc190cf-cafb-0310-a4f2-bffc1f526a37
---
 django/db/models/query.py             | 10 +++++++++-
 tests/modeltests/or_lookups/models.py | 15 +++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/django/db/models/query.py b/django/db/models/query.py
index 53ed63ae5b..f42e8cfd42 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -641,7 +641,15 @@ def get_where_clause(lookup_type, table_prefix, field_name, value):
     except KeyError:
         pass
     if lookup_type == 'in':
-        return '%s%s IN (%s)' % (table_prefix, field_name, ','.join(['%s' for v in value]))
+        in_string = ','.join(['%s' for id in value])
+        if in_string:
+            return '%s%s IN (%s)' % (table_prefix, field_name, in_string)
+        else:
+            # Most backends do not accept an empty string inside the IN
+            # expression, i.e. cannot do "WHERE ... IN ()".  Since there are
+            # also some backends that do not accept "WHERE false", we instead
+            # use an expression that always evaluates to False.
+            return '0=1'
     elif lookup_type == 'range':
         return '%s%s BETWEEN %%s AND %%s' % (table_prefix, field_name)
     elif lookup_type in ('year', 'month', 'day'):
diff --git a/tests/modeltests/or_lookups/models.py b/tests/modeltests/or_lookups/models.py
index 2de18edc1f..9f926a7373 100644
--- a/tests/modeltests/or_lookups/models.py
+++ b/tests/modeltests/or_lookups/models.py
@@ -69,6 +69,21 @@ __test__ = {'API_TESTS':"""
 >>> Article.objects.filter(Q(pk=1) | Q(pk=2) | Q(pk=3))
 [<Article: Hello>, <Article: Goodbye>, <Article: Hello and goodbye>]
 
+# You could also use "in" to accomplish the same as above.
+>>> Article.objects.filter(pk__in=[1,2,3])
+[<Article: Hello>, <Article: Goodbye>, <Article: Hello and goodbye>]
+
+>>> Article.objects.filter(pk__in=[1,2,3,4])
+[<Article: Hello>, <Article: Goodbye>, <Article: Hello and goodbye>]
+
+# Passing "in" an empty list returns no results ...
+>>> Article.objects.filter(pk__in=[])
+[]
+
+# ... but can return results if we OR it with another query.
+>>> Article.objects.filter(Q(pk__in=[]) | Q(headline__icontains='goodbye'))
+[<Article: Goodbye>, <Article: Hello and goodbye>]
+
 # Q arg objects are ANDed
 >>> Article.objects.filter(Q(headline__startswith='Hello'), Q(headline__contains='bye'))
 [<Article: Hello and goodbye>]