title: find records where field type is string
body: <p>I have this records :</p>
  
  <pre><code>{id : 1 , price : 5}
  {id : 2 , price : "6"}
  {id : 3 , price : 13}
  {id : 4 , price : "75"}
  </code></pre>
  
  <p>I want to build a query that get just record who have price with type "string"</p>
  
  <p>so, it will get : </p>
  
  <pre><code>{id : 2 , price : "6"}
  {id : 4 , price : "75"}
  </code></pre>