title: Google App Engine - Multiple child/parent
body: <p>I want to make friend system that have db model like this:</p>
  
  <pre><code>class Users(ndb.Model):
      username = ndb.StringProperty(required = True)
      bio = ndb.StringProperty()
  
  class friend_list(ndb.Model):
      list = ndb.StringProperty(repeated=True)
  
  class friend_pending(ndb.Model):
      list = ndb.StringProperty(repeated=True)
  </code></pre>
  
  <p>friend_pending is model for friend that not yet accepted. While friend_list is model for friend that are accepted.</p>
  
  <p>I want to make both friend_list and friend_pending to be child of Users entity. Is it possible?</p>
  
  <p>Here's the second approach if it is not possible:</p>
  
  <pre><code>    class Users(ndb.Model):
          username = ndb.StringProperty(required = True)
          bio = ndb.StringProperty()
  
      class friend_list(ndb.Model):
          user_username = ndb.StringProperty(required = True)
          list = ndb.StringProperty(repeated=True)
  
      class friend_pending(ndb.Model):
          user_username = ndb.StringProperty(required = True)
          list = ndb.StringProperty(repeated=True)
  </code></pre>
  
  <p>If both are possible, which are better for cost and performance?</p>