Fixed #19816: pre-evaluate queryset on m2m set

In ReverseManyRelatedObjectsDescriptor.__set__, evaluate possible
queryset to avoid problems when clear() would touch data this queryset
returns.

1 files changed, 14 insertions, 1 deletions

diff --git a/tests/regressiontests/m2m_regress/tests.py b/tests/regressiontests/m2m_regress/tests.py
index 3dc1d2417c..90aab5e2a5 100644
--- a/tests/regressiontests/m2m_regress/tests.py
+++ b/tests/regressiontests/m2m_regress/tests.py
@@ -5,7 +5,7 @@ from django.test import TestCase
 from django.utils import six
 
 from .models import (SelfRefer, Tag, TagCollection, Entry, SelfReferChild,
-    SelfReferChildSibling, Worksheet, RegressionModelSplit)
+    SelfReferChildSibling, Worksheet, RegressionModelSplit, Line)
 
 
 class M2MRegressionTests(TestCase):
@@ -96,3 +96,16 @@ class M2MRegressionTests(TestCase):
         # causes a TypeError in add_lazy_relation
         m1 = RegressionModelSplit(name='1')
         m1.save()
+
+    def test_m2m_filter(self):
+        worksheet = Worksheet.objects.create(id=1)
+        line_hi = Line.objects.create(name="hi")
+        line_bye = Line.objects.create(name="bye")
+
+        worksheet.lines = [line_hi, line_bye]
+        hi = worksheet.lines.filter(name="hi")
+
+        worksheet.lines = hi
+        self.assertEquals(1, worksheet.lines.count())
+        self.assertEquals(1, hi.count())
+