title: Google App Engine Updating schema in DB model
body: <p>I'm adding new  attribute to an existing data store model. I need to update an existing schema with data to the new schema. I have checked google's doc on <a href="https://cloud.google.com/appengine/articles/update_schema?csw=1" rel="nofollow">updating schema</a> and it uses ndb model.</p>
  
  <p>I have a DB model like this: </p>
  
  <pre><code>class oldModel(db.Model):
       name = db.StringProperty(default = "")
       author = db.StringProperty(default = "")
       created = db.DateTimeProperty(auto_now_add = True)
  </code></pre>
  
  <p>My new new schema is:</p>
  
  <pre><code>class oldModel(db.Model):
       name = db.StringProperty(default = "")
       author = db.StringProperty(default = "")
       created = db.DateTimeProperty(auto_now_add = True)
       # new field
       category = db.IntegerProperty(default = 0)  
  </code></pre>
  
  <p>How do you do it? (One thing I think of is to include the new schema with a different name and manually populate the data from old one to new schema and drop the old one)  </p>