Fixed #12663 -- Formalized the Model._meta API for retrieving fields.

Thanks to Russell Keith-Magee for mentoring this Google Summer of
Code 2014 project and everyone else who helped with the patch!

1 files changed, 4 insertions, 3 deletions

diff --git a/django/forms/models.py b/django/forms/models.py
index c57c8af0b9..443d0559a6 100644
--- a/django/forms/models.py
+++ b/django/forms/models.py
@@ -6,6 +6,7 @@ and database field objects.
 from __future__ import unicode_literals
 
 from collections import OrderedDict
+from itertools import chain
 import warnings
 
 from django.core.exceptions import (
@@ -89,7 +90,7 @@ def save_instance(form, instance, fields=None, fail_message='saved',
         # Note that for historical reasons we want to include also
         # virtual_fields here. (GenericRelation was previously a fake
         # m2m field).
-        for f in opts.many_to_many + opts.virtual_fields:
+        for f in chain(opts.many_to_many, opts.virtual_fields):
             if not hasattr(f, 'save_form_data'):
                 continue
             if fields and f.name not in fields:
@@ -127,7 +128,7 @@ def model_to_dict(instance, fields=None, exclude=None):
     from django.db.models.fields.related import ManyToManyField
     opts = instance._meta
     data = {}
-    for f in opts.concrete_fields + opts.virtual_fields + opts.many_to_many:
+    for f in chain(opts.concrete_fields, opts.virtual_fields, opts.many_to_many):
         if not getattr(f, 'editable', False):
             continue
         if fields and f.name not in fields:
@@ -186,7 +187,7 @@ def fields_for_model(model, fields=None, exclude=None, widgets=None,
     from django.db.models.fields import Field as ModelField
     sortable_virtual_fields = [f for f in opts.virtual_fields
                                if isinstance(f, ModelField)]
-    for f in sorted(opts.concrete_fields + sortable_virtual_fields + opts.many_to_many):
+    for f in sorted(chain(opts.concrete_fields, sortable_virtual_fields, opts.many_to_many)):
         if not getattr(f, 'editable', False):
             continue
         if fields is not None and f.name not in fields: