title: Returning only sub document based on subdocument _id which is the items of array field of the mongodb document
body: <p>My schema goes like this</p>
  
  <pre><code>  [
  {
      "_id" : ObjectId("565f0f5d77f0c7bd11bbadd8"),
      "blog_id" : ObjectId("56587befdb7224110f007233"),
      "comments" : [
          {
              "user_id" : ObjectId("562fa014888806820e21e0df"),
              "user_full_name" : "Niroj Paudel",
              "comment" : "pradip is bhole baba",
              "_id" : ObjectId("565f0f5d77f0c7bd11bbadd9"),
              "dt" : ISODate("2015-12-02T15:33:49.578Z")
          },
          {
              "user_id" : ObjectId("562fa014888806820e21e0df"),
              "user_full_name" : "Niroj Paudel",
              "comment" : "honkog pokhara... he he ha ha",
              "_id" : ObjectId("565f1034fd07cbfc1129db0b"),
              "dt" : ISODate("2015-12-02T15:37:24.581Z")
          }
      ],
      "record_count" : 2,
      "__v" : 0
  }]
  </code></pre>
  
  <p>What I am trying is to select particular item of comments array based on the blog_id and comments._id ..... but instead of returning only the particular comment it is returning the whole document .</p>
  
  <p>Currently I have following query </p>
  
  <pre><code>db.blog_comments..findOne({
             "blog_id" : ObjectId("56587befdb7224110f007233"),
             "comments._id":ObjectId("565f1034fd07cbfc1129db0b")
         })
  </code></pre>
  
  <p>This query is returning the whole document i.e.-</p>
  
  <pre><code>[
  {
      "_id" : ObjectId("565f0f5d77f0c7bd11bbadd8"),
      "blog_id" : ObjectId("56587befdb7224110f007233"),
      "comments" : [
          {
              "user_id" : ObjectId("562fa014888806820e21e0df"),
              "user_full_name" : "Niroj Paudel",
              "comment" : "pradip is bhole baba",
              "_id" : ObjectId("565f0f5d77f0c7bd11bbadd9"),
              "dt" : ISODate("2015-12-02T15:33:49.578Z")
          },
          {
              "user_id" : ObjectId("562fa014888806820e21e0df"),
              "user_full_name" : "Niroj Paudel",
              "comment" : "honkog pokhara... he he ha ha",
              "_id" : ObjectId("565f1034fd07cbfc1129db0b"),
              "dt" : ISODate("2015-12-02T15:37:24.581Z")
          }
      ],
      "record_count" : 2,
      "__v" : 0
  }]
  </code></pre>
  
  <p>but I want just this</p>
  
  <pre><code>[{
                  "user_id" : ObjectId("562fa014888806820e21e0df"),
                  "user_full_name" : "Niroj Paudel",
                  "comment" : "honkog pokhara... he he ha ha",
                  "_id" : ObjectId("565f1034fd07cbfc1129db0b"),
                  "dt" : ISODate("2015-12-02T15:37:24.581Z")
   }]
  </code></pre>
  
  <p>What I am missing please suggest..
  Thank you</p>