title: Data type issue in aggregation in mongo db
body: <p>I have written following code for aggregation of two tables in php application</p>
  
  <pre><code>    $lookupTwo = array(
          '$lookup'=&gt; array(
              "from" =&gt; "studentTbl",
              "localField" =&gt; "studentDetailId",
              "foreignField" =&gt; "studentId",
              "as" =&gt; "recieverDetails"
          )
      );
  </code></pre>
  
  <p>Now I am facing an issue, the <code>studentDetailId</code> field is stored as a string and  <code>studentId</code> is stored as an integer. </p>
  
  <p>The above query will return empty result. </p>
  
  <ul>
  <li>Is there any possibility for performing aggregation in such case?</li>
  </ul>