title: Select and order all subdocuments from a collection
body: <p>I have the following documents in a collection:</p>
  
  <pre><code>{
    "thread_object": "Sed consectetur, massa id aliquam lacinia",
    "thread_comments": [
      {
        "comment_date": "11/01/2014 17:23:19",
        "comment_user": "Integer",
        "comment_content": "In suscipit enim at eleifend auctor"
      },
      {
        "comment_date": "12/01/2014 17:23:19",
        "comment_user": "Suspendisse",
        "comment_content": "Quisque facilisis magna pellentesque diam mollis"
      }
    ]
  },
  {
    "thread_object": "Vivamus auctor mauris augue",
    "thread_comments": []
  },
  {
    "thread_object": "Phasellus volutpat, sem id convallis elementum",
    "thread_comments": [
      {
        "comment_date": "10/01/2014 17:23:19",
        "comment_user": "Donec",
        "comment_content": "Suspendisse a pellentesque justo"
      }
    ]
  }
  </code></pre>
  
  <p>How can I retrieve an ordered list of all the comments?</p>
  
  <pre><code>{
    "comment_date": "10/01/2014 17:23:19",
    "comment_user": "Donec",
    "comment_content": "Suspendisse a pellentesque justo"
  },
  {
    "comment_date": "11/01/2014 17:23:19",
    "comment_user": "Integer",
    "comment_content": "In suscipit enim at eleifend auctor"
  },
  {
    "comment_date": "12/01/2014 17:23:19",
    "comment_user": "Suspendisse",
    "comment_content": "Quisque facilisis magna pellentesque diam mollis"
  },
  </code></pre>