[1.5.x] Fixed Oracle failure caused by None converted to '' in select_related case

Backpatch of c159d9cec0baab7bbd04d5d51a92a51e354a722a

1 files changed, 9 insertions, 2 deletions

diff --git a/django/db/models/query.py b/django/db/models/query.py
index dc1ddf1606..da4c69f362 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -1418,8 +1418,15 @@ def get_cached_row(row, index_start, using,  klass_info, offset=0):
     fields = row[index_start : index_start + field_count]
     # If all the select_related columns are None, then the related
     # object must be non-existent - set the relation to None.
-    # Otherwise, construct the related object.
-    if fields == (None,) * field_count:
+    # Otherwise, construct the related object. Also, some backends treat ''
+    # and None equivalently for char fields, so we have to be prepared for
+    # '' values.
+    if connections[using].features.interprets_empty_strings_as_nulls:
+        vals = tuple([None if f == '' else f for f in fields])
+    else:
+        vals = fields
+
+    if vals == (None,) * field_count:
         obj = None
     else:
         if field_names: