1 files changed, 39 insertions, 0 deletions
diff --git a/tests/modeltests/expressions/tests.py b/tests/modeltests/expressions/tests.py
index 99eb07e370..ca47521ccd 100644
--- a/tests/modeltests/expressions/tests.py
+++ b/tests/modeltests/expressions/tests.py
@@ -219,3 +219,42 @@ class ExpressionsTests(TestCase):
         )
         acme.num_employees = F("num_employees") + 16
         self.assertRaises(TypeError, acme.save)
+
+    def test_ticket_18375_join_reuse(self):
+        # Test that reverse multijoin F() references and the lookup target
+        # the same join. Pre #18375 the F() join was generated first, and the
+        # lookup couldn't reuse that join.
+        qs = Employee.objects.filter(
+            company_ceo_set__num_chairs=F('company_ceo_set__num_employees'))
+        self.assertEqual(str(qs.query).count('JOIN'), 1)
+
+    def test_ticket_18375_kwarg_ordering(self):
+        # The next query was dict-randomization dependent - if the "gte=1"
+        # was seen first, then the F() will reuse the join generated by the
+        # gte lookup, if F() was seen first, then it generated a join the
+        # other lookups could not reuse.
+        qs = Employee.objects.filter(
+            company_ceo_set__num_chairs=F('company_ceo_set__num_employees'),
+            company_ceo_set__num_chairs__gte=1)
+        self.assertEqual(str(qs.query).count('JOIN'), 1)
+
+    def test_ticket_18375_kwarg_ordering_2(self):
+        # Another similar case for F() than above. Now we have the same join
+        # in two filter kwargs, one in the lhs lookup, one in F. Here pre
+        # #18375 the amount of joins generated was random if dict
+        # randomization was enabled, that is the generated query dependend
+        # on which clause was seen first.
+        qs = Employee.objects.filter(
+            company_ceo_set__num_employees=F('pk'),
+            pk=F('company_ceo_set__num_employees')
+        )
+        self.assertEqual(str(qs.query).count('JOIN'), 1)
+
+    def test_ticket_18375_chained_filters(self):
+        # Test that F() expressions do not reuse joins from previous filter.
+        qs = Employee.objects.filter(
+            company_ceo_set__num_employees=F('pk')
+        ).filter(
+            company_ceo_set__num_employees=F('company_ceo_set__num_employees')
+        )
+        self.assertEqual(str(qs.query).count('JOIN'), 2)