title: can terms lookup mechanism query be nested
body: <p>I want to know can I nest a terms lookup mechanism query in anther terms lookup mechanism.
  For instance:</p>
  
  <pre><code>curl -XPUT localhost:9200/users/user/2 -d '{
     "tweets" : ["1", "3"]
  }'
  
  curl -XPUT localhost:9200/tweets/tweet/1 -d '{
     "uuid" : "1",
     "comments":["1","2","3"]
  }'
  
  curl -XPUT localhost:9200/comments/comment/1 -d '{
     "uuid" : "1"
  }'
  </code></pre>
  
  <p>As you know, we can use a terms lookup mechanism query to get tweets which belong to the user:</p>
  
  <pre><code>curl -XGET localhost:9200/tweets/tweet/_search -d'{
    "query" : {
      "terms" : {
        "uuid" : {
          "index" : "users",
          "type" : "user",
          "id" : "2",
          "path" : "tweets"
        }
      }
    }
  }'
  </code></pre>
  
  <p>But if i want to get comments, i must do anther query. 
  However my documents is so many, it is not a good method.
  So i want to nest terms lookup query in order to get comments in only one query by user's id, can i?
  I will so appreciate it, if you can give me some help. Thank you! :)</p>