Fixed incorrect 'select' generation.

generate.py

@@ -123,7 +123,7 @@ class Model(object):
         relopts = kwargs
 
         if self.options.get('create_select', True):
-            relopts['select'] = model.accessible_attr
+            relopts['select'] = ', '.join(model.accessible_attr)
 
         return relopts