def get_url(self, obj):
if obj is None:
return None
if obj.is_latest_version:
try:
return Mapping.objects.get(id=obj.versioned_object_id).url
except Mapping.DoesNotExist:
raise Mapping.DoesNotExist('Mapping with id %s does not exist' % obj.versioned_object_id)
return obj.url
