title: How to query on all Expando entities that have a certain dynamic property?
body: <p>I want to query the datastore for Expando entities that have a certain dynamic property filled out. That property, however, is not a boolean. I want to get all the entities that have a certain dynamic property filled out.</p>
  
  <pre><code>class Entity(db.Expando):
      name = db.StringProperty()
  
  #I want to query something like this
  entities = Entity.all().filter('address') #note below
  </code></pre>
  
  <p>Note: I just want to query all entities that have the dynamic property address filled out. I'm not querying if their address matches so and so.</p>
  
  <p>Is that possible? How?</p>
  
  <p>Thanks!</p>