title: MongoDB query multiple collections at once
body: <pre><code>users
  {
   "_id":"12345",
   "admin":1
  },
  {
   "_id":"123456789",
   "admin":0
  }
  
  posts
  {
   "content":"Some content",
   "owner_id":"12345",
   "via":"facebook"
  },
  {
   "content":"Some other content",
   "owner_id":"123456789",
   "via":"facebook"
  }
  </code></pre>
  
  <p>Here is a sample from my mongodb.  I want to get all the posts which has "via" attribute equal to "facebook" and posted by an admin ("admin":1).  I couldn't figure out how to acquire this query.  Since mongodb is not a relational database, I couldn't do a join operation.  What could be the solution ?</p>