title: Nested field_value_factor on individual field
body: <p>I have some document with mapping looks like following</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>{  
     "documents":[  
        {  
           "author":"name1",
           "books":[  
              {  
                 "title":"title1",
                 "content":"content1",
                 "rating":5
              },
              {  
                 "title":"title2",
                 "content":"content2",
                 "rating":1
              }
           ]
        },
        {  
           "author":"name2",
           "books":[  
              {  
                 "title":"title1",
                 "content":"content1",
                 "rating":3
              },
              {  
                 "title":"title2",
                 "content":"content2",
                 "rating":3
              }
           ]
        }
     ]
  }</code></pre>
  </div>
  </div>
  </p>
  
  <p>I want to return a list of authors whose book contents match certain keywords. But at the same time, I want the score on each documents.books.content is boosted by documents.books.rating, then combine these score together. </p>
  
  <p>Anyway, I can do that with function score?</p>
  
  <p>Thank you!</p>