Ticket #17668: 17668.diff

django/db/models/query.py

@@ -82 +82 @@
             if self._iter:
                 self._result_cache = list(self._iter)
             else:
-                self._result_cache = list(self.iterator())
+                self._result_cache = list(self.iterator(_check_prefetch=False))
         elif self._iter:
             self._result_cache.extend(self._iter)
         if self._prefetch_related_lookups and not self._prefetch_done:
@@ -228 +228 @@
     # METHODS THAT DO DATABASE QUERIES #
     ####################################
 
-    def iterator(self):
+    def iterator(self, _check_prefetch=True):
         """
         An iterator over the results from applying this QuerySet to the
         database.
+
+        Calling this method with _check_prefetch=True will cause an error
+        if there are prefetches defined for the qs. Internal methods can
+        skip prefetch_related checks by defining _check_prefetch=False.
         """
+        if _check_prefetch and self._prefetch_related_lookups:
+            raise ValueError("Using iterator() when prefetch_related is used "
+                             "is not supported")
         fill_cache = False
         if connections[self.db].features.supports_select_related:
             fill_cache = self.query.select_related
@@ -485 +492 @@
         qs = self._clone()
         qs.query.add_filter(('pk__in', id_list))
         qs.query.clear_ordering(force_empty=True)
-        return dict([(obj._get_pk_val(), obj) for obj in qs.iterator()])
+        # Populate the query, making sure prefetch_related etc. are handled
+        # properly.
+        objs = list(self)
+        return dict([(obj._get_pk_val(), obj) for obj in objs])
 
     def delete(self):
         """

docs/ref/models/querysets.txt

@@ -1430 +1430 @@
 Note that using ``iterator()`` on a ``QuerySet`` which has already been
 evaluated will force it to evaluate again, repeating the query.
 
+It is an error to use ``iterator()`` when ``prefetch_related`` is also used
+in the same ``QuerySet``.
+
 latest
 ~~~~~~
 

tests/modeltests/prefetch_related/tests.py

@@ -470 +470 @@
                         for e in qs2]
 
         self.assertEqual(co_serfs, co_serfs2)
+
+class TestIterator(TestCase):
+
+    def test_iterator_raises_error(self):
+        """
+        Using an iterator when prefetch_related is defined is an error.
+        """
+        def raises():
+            list(Employee.objects.prefetch_related('boss').iterator())
+        self.assertRaises(ValueError, raises)
+
+    def test_in_bulk(self):
+        """
+        In-bulk does correctly prefetch objects by not using .iterator()
+        directly.
+        """
+        boss = Employee.objects.create(name="Peter")
+        boss = Employee.objects.create(name="Jack")
+        with self.assertNumQueries(2):
+            # Check that prefetch is done and it does not cause any errors.
+            bulk = Employee.objects.prefetch_related('serfs').in_bulk([boss.pk])
+            for b in bulk.values():
+                list(b.serfs.all())