title: Querying google datastore by key and sorting by another property
body: <p>I am using the low level datastore interface in java. I have an entity that stores a collection of Keys. I would like to query the datastore to get all of the entities in the collection. However, I'd also like to sort them on a created date property. So, I'd like to do something like this:</p>
  
  <pre><code>Query query = new Query(EndeavorUpdate.ENDEAVOR_UPDATE_ENTITY_TYPE);
  //getEndeavorUpdateIds() returns a List &lt; Key &gt;
  query.addFilter("__key__", Query.FilterOperator.EQUAL, getEndeavorUpdateIds());
  query.addSort(EndeavorUpdate.CREATED_DATE_PROPERTY);
  PreparedQuery pq = ds.prepare(query);
  </code></pre>
  
  <p>However, I get an exception saying that "a collection of values is not allowed". It does work if I use IN instead of EQUAL but that seems tremendously inefficient. </p>
  
  <p>Is there a way to do this query efficiently or should I get all the entities from the datastore and do the sorting myself?</p>