title: Django Mongoengine EmbeddedDocument query issue
body: <p>my model is about a list of top movies</p>
  
  <pre><code>class Movie(Document):
      title = StringField()
        ...
      ranks = ListField(EmbeddedDocumentField('Rank'))
  
  class Rank(EmbeddedDocument):     
      rank = IntField()
      imdb_rating = FloatField()
      date = StringField(required=True)
  </code></pre>
  
  <p>How can I write a query to get only the movies have Rank record in today?</p>