[1.6.x] Fixed #21410 -- prefetch_related() for ForeignKeys with related_name='+'

Regression introduced by commit 9777442.

Thanks to trac username troygrosfield for the report and test case.

Backpatch of cb83448891f2920c926f61826d8eae4051a3d8f2 from master.

Conflicts:

	tests/prefetch_related/models.py

1 files changed, 11 insertions, 1 deletions

diff --git a/django/db/models/fields/related.py b/django/db/models/fields/related.py
index 2813a39567..d50c72d66c 100644
--- a/django/db/models/fields/related.py
+++ b/django/db/models/fields/related.py
@@ -273,7 +273,17 @@ class ReverseSingleRelatedObjectDescriptor(six.with_metaclass(RenameRelatedObjec
         rel_obj_attr = self.field.get_foreign_related_value
         instance_attr = self.field.get_local_related_value
         instances_dict = dict((instance_attr(inst), inst) for inst in instances)
-        query = {'%s__in' % self.field.related_query_name(): instances}
+        related_field = self.field.foreign_related_fields[0]
+
+        # FIXME: This will need to be revisited when we introduce support for
+        # composite fields. In the meantime we take this practical approach to
+        # solve a regression on 1.6 when the reverse manager in hidden
+        # (related_name ends with a '+'). Refs #21410.
+        if self.field.rel.is_hidden():
+            query = {'%s__in' % related_field.name: set(instance_attr(inst)[0] for inst in instances)}
+        else:
+            query = {'%s__in' % self.field.related_query_name(): instances}
+
         qs = self.get_queryset(instance=instances[0]).filter(**query)
         # Since we're going to assign directly in the cache,
         # we must manage the reverse relation cache manually.