title: how to count number of sub object (same document) in mongodb
body: <p>Example document:</p>
  
  <pre><code>{
      "aliases" : {
          "name" : [ 
              "Brinton McKay", 
              "Dr. Theopolis", 
              "Galactic Spiral Sound", 
              "Highrise", 
              "Memory Boy", 
              "Semblance Factor", 
              "Spy (2)", 
              "Three O'Clock High"]}
  }
  </code></pre>
  
  <p>How i can count the number of "name" under  "aliases"? 
  I would like to print all _id who which contains more than 3 aliases. 
  any help would be appreciated.</p>