title: Aggregation in flask-mongoengine
body: <p>I'm just staring out with MongoDB and I'm staring an application with flask-mongoengine and I want to aggregate a few documents.</p>
  
  <p>I'm using flask-mongoengine and when trying</p>
  
  <pre><code>class MyDocumentModel(db.Document):
    name = db.StringField(max_length=55)
  
  MyDocumentModel.objects.aggregate()
  </code></pre>
  
  <p>I get the error:</p>
  
  <blockquote>
    <p>AttributeError: 'BaseQuerySet' object has no attribute 'aggregate'</p>
  </blockquote>