title: For Mongodb is it better to reference an object or use a natural String key?
body: <p>I am building a corpus of indexed sentences in different languages. I have a collection of Languages which have both an ObjectId and the ISO code as a key. Is it better to use a reference to the Language collection or store a key like "en" or "fr"?</p>
  
  <p>I suppose it's a compromise between:</p>
  
  <ul>
  <li>ease of referencing the Language</li>
  <li>object in that collection</li>
  <li>speed in doing queries where the sentence has a certain language</li>
  <li>the size of the data on disk</li>
  </ul>
  
  <p>Any best practices that I should know of?</p>