[1.1.X] Fixed #12546. Objects with a __len__ that returns 0 can now be serialized. Thanks, casobn for the report and Alex Gaynor for the patch and tests. Backport of r12576 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@12577 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/fields/__init__.py

@@ -277,7 +277,7 @@ class Field(object):
         return first_choice + list(self.flatchoices)
 
     def _get_val_from_obj(self, obj):
-        if obj:
+        if obj is not None:
             return getattr(obj, self.attname)
         else:
             return self.get_default()

tests/regressiontests/serializers_regress/models.py

@@ -252,4 +252,9 @@ class InheritBaseModel(BaseModel):
 class ExplicitInheritBaseModel(BaseModel):
     parent = models.OneToOneField(BaseModel)
     child_data = models.IntegerField()
-    
+
+class LengthModel(models.Model):
+    data = models.IntegerField()
+
+    def __len__(self):
+        return self.data

tests/regressiontests/serializers_regress/tests.py

@@ -8,7 +8,8 @@ forward, backwards and self references.
 """
 
 
-import unittest, datetime
+import datetime
+import unittest
 from cStringIO import StringIO
 
 from django.utils.functional import curry
@@ -321,6 +322,8 @@ The end."""),
     (inherited_obj, 900, InheritAbstractModel, {'child_data':37,'parent_data':42}),
     (inherited_obj, 910, ExplicitInheritBaseModel, {'child_data':37,'parent_data':42}),
     (inherited_obj, 920, InheritBaseModel, {'child_data':37,'parent_data':42}),
+    (data_obj, 1004, LengthModel, 0),
+    (data_obj, 1005, LengthModel, 1),
 ]
 
 # Because Oracle treats the empty string as NULL, Oracle is expected to fail