title: Two mongodb collections in one query
body: <p>I have a big collection of clients and a huge collection of the clients data, the collections are separated and I don't want to combine them to a single collection (because of the other already working servlets) but now I need to "Join" data from both collection in a single result.</p>
  
  <p>Since The query should return a big number of results I don't want to query the server once and then use the result to query again. I'm also concerned about the traffic between the server and the DB and the memory that the result set will occupy in the server RAM.</p>
  
  <p>The way it's working now is that I get the relevant client list from the 'clients' collection and send this list to the query of the 'client data' collection and only then I get the aggregated results.</p>
  
  <p>I want to cut off the getting and sending the client list from and right back to the server, get the server to ask himself, let the query of client data collection to ask clients collection for the relevant client list.</p>
  
  <p>How can I use a stored procedure(javascript functions) to do the query in the DB and return only the relevant clients out of the collection.
  Alternatively, Is there a way to write a query that joins result from another collection ?</p>