title: mongo db findOne and $or does order of arguments matters or hierarchy? [performance]
body: <p>I mean for example while having two conditions: if first condition true will it avoid checking the second?</p>
  
  <pre><code>doc = collection.find_one(
      {'$or': [
                {
                 'k': kind,
                 'i': int(pk)
                },
                {
                 'children.k': kind, 
                 'children.i': int(pk)
                }
  
              ]
      }, { '_id': False})
  </code></pre>
  
  <p>I would like that it stops further searching when matching first condition, so it not goes lower level to search around children.</p>
  
  <p>Is it matter of arguments order in <code>$OR</code> closure or rather mongodb knows smartly the hierarchy and it influences order of search by <code>findOne</code>?</p>