title: Query MongoDB with a regex expression against an ObjectId
body: <p>Is it possible to do a query like:</p>
  
  <pre><code>db.artigo.find( { _id : ObjectId('520a504a3004bc615fcfcf16') } )
  </code></pre>
  
  <p>but using a regex on ObjectId?</p>
  
  <p>For example, do get _ids that contains "004" on that position above.</p>
  
  <p>PS. The reason is to implement a shorty service based on some fields, namely the _id. I'm trying to create an implicit "shorty" service instead of an explicit one (with a field generated for the purpose).</p>