title: MongoDB - reference a document within a document
body: <p>I want to reference a parent document within an embedded document, is this possible? I want to do this because I have users who have images who have comments... so i want a comment to be by a specific user.
  This is my structure:</p>
  
  <pre><code>db.site_users.insert([
  {
      email: 'pbrown@hotmail.co.uk',
      password: 
      fullName: 'Peter Brown',
      images: [
          {
              title: 'Here is a sample title',
              location: 'here is a sample location',
              imageURLs: ['http://exmaple.com/uploads/39873874.jpg', 'http://example.com/uploads/7844656.jpg'],
              tags: ['tagone', 'tagtwo'],
              comments: [
                  {
                      site_users_id: '',
                      comment: 'Yes definately agree with you',
                  }
               ]
           }
  }])
  </code></pre>
  
  <p>It is the site_users_id within the comment that I am not sure about, I thought this could be the object ID of another user that exists within the same document. is this the correct way to reference another user? or is there a better way?
  Thanks in advance. </p>