Ticket #16043: 16043-testcase.patch

modeltests/select_related/tests.py

@@ +1 @@
+from __future__ import with_statement
+
 from django.test import TestCase
 
 from models import Domain, Kingdom, Phylum, Klass, Order, Family, Genus, Species
+from models import KingdomOnPlanet
 
 class SelectRelatedTests(TestCase):
 
@@ -166 +169 @@
             Species.objects.select_related,
             'genus__family__order', depth=4
         )
+
+    def test_issue_16043(self):
+        """
+        Regression test for #16043.
+        If the parent class has a foreign key to another object, make sure
+        that the target of the foreign key is cached for both the parent and
+        the child.
+        """
+        related = Domain.objects.create(name='Eukaryota')
+        child = KingdomOnPlanet.objects.create(name='Protista', planet='Earth',
+                domain=related)
+        # 1 SQL request needed
+        with self.assertNumQueries(1):
+            parent = Kingdom.objects.select_related('domain').get(name='Protista')
+        # no SQL needed, thanks to select_related
+        with self.assertNumQueries(0):
+            parent.domain
+        # 1 SQL request needed to obtain the specialization
+        with self.assertNumQueries(1):
+            child = parent.kingdomonplanet
+        # no SQL needed, the related object was cached at step 2
+        with self.assertNumQueries(0):
+            child.domain

modeltests/select_related/models.py

@@ -56 +56 @@
     name = models.CharField(max_length=50)
     genus = models.ForeignKey(Genus)
     def __unicode__(self):
-        return self.name
- No newline at end of file
+        return self.name
+
+# Sorry, we need some science-fiction too.
+
+class KingdomOnPlanet(Kingdom):
+    planet = models.CharField(max_length=50)