Fixed #27159 -- Prevented pickling a query with an __in=inner_qs lookup from evaluating inner_qs.

django/db/models/fields/related_lookups.py

@@ -83,6 +83,25 @@ class RelatedIn(In):
         else:
             return super(RelatedIn, self).as_sql(compiler, connection)
 
+    def __getstate__(self):
+        """
+        Prevent pickling a query with an __in=inner_qs lookup from evaluating
+        inner_qs.
+        """
+        from django.db.models.query import QuerySet  # Avoid circular import
+        state = self.__dict__.copy()
+        if isinstance(self.rhs, QuerySet):
+            state['rhs'] = (self.rhs.__class__, self.rhs.query)
+        return state
+
+    def __setstate__(self, state):
+        self.__dict__.update(state)
+        if isinstance(self.rhs, tuple):
+            queryset_class, query = self.rhs
+            queryset = queryset_class()
+            queryset.query = query
+            self.rhs = queryset
+
 
 class RelatedLookupMixin(object):
     def get_prep_lookup(self):

tests/queryset_pickle/tests.py

@@ -153,3 +153,42 @@ class PickleabilityTestCase(TestCase):
         msg = "Pickled queryset instance's Django version 1.0 does not match the current version %s." % get_version()
         with self.assertRaisesMessage(RuntimeWarning, msg):
             pickle.loads(pickle.dumps(qs))
+
+
+class InLookupTests(TestCase):
+
+    @classmethod
+    def setUpTestData(cls):
+        for i in range(1, 3):
+            group = Group.objects.create(name='Group {}'.format(i))
+        cls.e1 = Event.objects.create(title='Event 1', group=group)
+
+    def test_in_lookup_queryset_evaluation(self):
+        """
+        Neither pickling nor unpickling a QuerySet.query with an __in=inner_qs
+        lookup should evaluate inner_qs.
+        """
+        events = Event.objects.filter(group__in=Group.objects.all())
+
+        with self.assertNumQueries(0):
+            dumped = pickle.dumps(events.query)
+
+        with self.assertNumQueries(0):
+            reloaded = pickle.loads(dumped)
+            reloaded_events = Event.objects.none()
+            reloaded_events.query = reloaded
+
+        self.assertSequenceEqual(reloaded_events, [self.e1])
+
+    def test_in_lookup_query_evaluation(self):
+        events = Event.objects.filter(group__in=Group.objects.values('id').query)
+
+        with self.assertNumQueries(0):
+            dumped = pickle.dumps(events.query)
+
+        with self.assertNumQueries(0):
+            reloaded = pickle.loads(dumped)
+            reloaded_events = Event.objects.none()
+            reloaded_events.query = reloaded
+
+        self.assertSequenceEqual(reloaded_events, [self.e1])