title: Mongo Lookup join in collections using $id reference
body: <p>I have a collection called post with references to two other collections: status, format</p>
  
  <pre><code>post:
  {
      "_id" : ObjectId("5d7c1c4549c5e277395871ad"),
      "status" : {
          "$ref" : "status",
          "$id" : ObjectId("status123")
      },
      "format" : {
          "$ref" : "format",
          "$id" : ObjectId("format123")
      }
  }
  
  status:
  {
      "_id" : ObjectId("status123"),
      "name" : "Draft"
  }
  
  format:
  {
      "_id" : ObjectId("format123"),
      "name" : "Standard"
  }
  </code></pre>
  
  <p>I would like the query for post to return the following:</p>
  
  <pre><code>post:
  {
      "_id" : ObjectId("5d7c1c4549c5e277395871ad"),
      "status" : {
          "_id" : ObjectId("status123"),
          "name" : "Draft"
      },
      "format" : {
          "_id" : ObjectId("format123"),
          "name" : "Standard"
      }
  }
  </code></pre>
  
  <p>What should my Mongo Query be? I am new with using MongoDB, any help is greatly appreciated.</p>
  
  <p>Thanks,
  Shashi</p>