title: mongoose/mongoDB query by one field distinct by another
body: <p>i have a collection with the following document as an example:</p>
  
  <pre><code>{
      _id: ObjectId("56fbf2210309775d6790c1c0"),
      city_id: 2600,
      street_name: "hamilton",
      branch: 6
  }
  </code></pre>
  
  <p>Is it possible to query the collection by branch but use a distinct on the street_name?</p>
  
  <p>Thanks!</p>