title: How to query through a DBRef in MongoDB/pymongo?
body: <p>Is it possible to query <em>through</em> a DBRef using a single find spec?</p>
  
  <p><strong>user collection</strong></p>
  
  <pre><code>{
      'age': 30
  }
  </code></pre>
  
  <p><strong>post collection</strong></p>
  
  <pre><code>{
      'user': DBRef('user', ...)
  }
  </code></pre>
  
  <p>Is it possible to query for all post who's users are 30 in a single find step?  If not, would it be wise to create a javascript function to handle the multi-stage operation or will that cause blocking problems?</p>