support nulls_last in sqlite

ox/django/query.py

@@ -25,7 +25,20 @@ class SQLCompiler(SQLCompiler):
     def get_ordering(self):
         result, group_by = super(SQLCompiler, self).get_ordering()
         if self.query.nulls_last and len(result):
+            if self.connection.vendor == 'sqlite':
+                _result = []
+                for r in result:
+                    if r.endswith(' DESC'):
+                        _r = r[:-len(' DESC')]
+                    elif r.endswith(' ASC'):
+                        _r = r[:-len(' ASC')]
+                    _result.append(_r + ' IS NULL')
+                    _result.append(r)
+
+                result = _result
+            else:
                 result = map(lambda e: e + ' NULLS LAST', result)
+            print result
         return result, group_by
 
 class Query(Query):