title: passing url parameter to $match query in mongodb
body: <p>How can I take ObjectId from Url parameter to obtain a data in Aggregate $match?
  For example, I have userID and I want to match teacher fields with userID which I pass to the URL parameter?
  it is like this</p>
  <pre><code>{ 
     $match : 
     { 
     &quot;teacher&quot; : req.params.id
     }
  }, 
  </code></pre>