title: Datastore App Engine quering ancestor python
body: <p>Hello I'm new on Datastore and on Python and I have a basic question but it can help me to understand more the Google cloud. </p>
  
  <p>I have 4 entities and let's say I have a parent (match) with children : team, player and event. </p>
  
  <pre><code>class Team(ndb.Model):
      d_name = ndb.StringProperty()
      d_side = ndb.StringProperty()
  
  class Player(ndb.Model):
      d_name = ndb.StringProperty()
      date_of_birth = ndb.StringProperty()
      d_position = ndb.StringProperty()
      d_teamKey = ndb.StringProperty()
  
  
  class Match(ndb.Model):
      d_competition_name = ndb.StringProperty()
      d_date = ndb.StringProperty()
      d_pool = ndb.StringProperty()
      d_season = ndb.StringProperty()
      d_team1Key = ndb.StringProperty()
      d_team2Key = ndb.StringProperty()
      d_winning_teamKey = ndb.StringProperty()
      d_match_id = ndb.StringProperty()
      d_match_day = ndb.IntegerProperty()
  
  class Event(ndb.Expando):
      d_teamKey = ndb.StringProperty()
      d_playerKey = ndb.StringProperty()
  </code></pre>
  
  <p>I know that the query if I want all the matchs day 4 is : </p>
  
  <pre><code>q = ndb.gql("SELECT * FROM Match WHERE d_match_day = 4")
  </code></pre>
  
  <p>But how can I seach all the players in theses match's children so that I have all the players who have played during the day 4 ? </p>
  
  <p>Thank you ! </p>