title: Mongoengine: How to append a new document to an Embedded ListField document?
body: <p>I would like to append a new ListField EmbeddedDocument to an existing ListField EmbeddedDocument document. In other words appending a new document to list that belongs to a a document in list.</p>
  
  <p>My Model: A Post can contain several Comments, each comment can have several Likes:</p>
  
  <pre><code>class Post(Document):
      txt = StringField()
      comments = ListField(EmbeddedDocumentField(Comment))
  
  class Comment(EmbeddedDocument):
      comment = StringField()
      comment_id = ObjectIdField()
      likes = ListField(EmbeddedDocumentField(Like))
  
  class Like(EmbeddedDocument):
      user = ReferenceField(User)
      date = DateTimeField(default=datetime.utcnow,required=True)
  </code></pre>
  
  <p>My Code: (it's not working 'append' command dosen't exists, only 'set' exists)</p>
  
  <pre><code>def appendNewLike():
      user = {..}
      target = ObjectId(commentId)
      newLike = Like(user=user)
      Product.objects(comments__comment_id=target).update(append_comments__S__likes=newLike)
  </code></pre>
  
  <p>Ideal solution would be something like:</p>
  
  <pre><code>def appendNewLike():
      user = {..}
      target = ObjectId(commentId)
      newLike = Like(user=user)
      Product.objects(comments__comment_id=target).comments.likes.append(newLike)
  </code></pre>
  
  <p>Comments? Suggestions?</p>