title: MongoDb array intersection
body: <p>Let's assume we have</p>
  
  <pre><code>post1.tags = [ '1', '2', '3' ];
  
  post2.tags = [ '2', '4', '5' ];
  
  post3.tags = [ '1', '3', '4' ];
  
  post4.tags = [ '1', '3', '4', '5', '6' ];
  </code></pre>
  
  <p>I'm trying to find posts which are containing 2 or more of the given tags [ '1', '3', '5' ].
  The result should be post1, post3 and post4. How can write a mongodb query to achieve this?</p>