title: SQLAlchemy how to get Column values from association table in many to many relationship
body: <p>I have Playlist and Tracks class and assigned Foreign keys to playlistsTracks. all ok when want to get Playlist tracks i use playlist.tracks. But now i need to also get the 'id' of the playlistsTracks. How can i get the 'id' or any extra column from association table?</p>
  
  <pre><code>playlistsTracks = db.Table('tbl_test_playlisttracks',
                      db.Column('id', db.Integer, primary_key=True),
                      db.Column('playlist_id', db.Integer, db.ForeignKey('tbl_test_playlists.id', ondelete='CASCADE')),
                      db.Column('track_id', db.Integer, db.ForeignKey('tbl_tracks.id'))
                      )
  
  
  
  class Track(db.Model):
  __tablename__ = 'tbl_tracks'
  
  id = db.Column(db.Integer, primary_key=True)
  name = db.Column(db.String(255))
  audio_url = db.Column(db.Text)
  movie_id = db.Column(db.Integer)
  entry = db.relationship('Playlist', secondary=playlistsTracks, backref=db.backref('tracks', lazy='dynamic'))
  
  
  
  class Playlist(db.Model):
  __tablename__ = 'tbl_test_playlists'
  
  id = db.Column(db.Integer, primary_key=True)
  name = db.Column(db.String(255))
  user_id = db.Column(db.String(255))
  current_rev = db.Column(db.Integer, default=0)
  </code></pre>