title: MongoDB Querying for object property in list
body: <p>Let's say I do have a document like this:</p>
  
  <pre><code>{
      _id: "cow",
      comments: [
          {user: "karl", comment: "I like cows.", at: /*a date*/},
          {user: "harry", comment: "Cows are the best.", at: /*a date*/}
      ]
  }
  </code></pre>
  
  <p>Now I want to collect all the comments that <code>"karl"</code> left in my db. Or just the ones on a certain date. The <code>"comments"</code> are indexed, how can I query for that?</p>