title: Google App Engine: Change thousands of entities at once?
body: <p>Basically, I would like to update about 10,000 entities at once — adding a new property and value to each entity.</p>
  
  <p>Given this class:</p>
  
  <pre><code>Post(ndb.Model):
      title = ndb.StringProperty()
      created_date = ndb.DateTimeProperty()
  </code></pre>
  
  <p>I would like to run some sort of operation that would create this new <code>created_date_string</code> property in my existing <code>Post</code> entities and occupying the field with a string version of the date. </p>
  
  <pre><code>Post(ndb.Model):
      title = ndb.StringProperty()
      created_date = ndb.DateTimeProperty()
      created_date_string = ndb.StringProperty(required=True)
  </code></pre>
  
  <p>How do I handle this? </p>
  
  <p>My best guess is to use task queues to update each entity; we would be queueing 10,000 tasks. Is there a better approach?</p>