title: Mongoose: save() is not a function when using find() and atributing value to variable
body: <p>This is the basic structure of the Schema I am working with using mongoose:</p>
  <pre class="lang-js prettyprint-override"><code>  const User = {
      uid: {
        type: String
      },
      routes: {
        type: Array
      }
     }
  </code></pre>
  <p>In my application there is a POST to <kbd>/route</kbd>, in which <strong>uid</strong> and a new <strong>route</strong> are provided as &quot;body parameters&quot;. In order to add to the <em>routes</em> array, I wrote a code similar to this (the only diference is that I check if the route already exists):</p>
  <pre class="lang-js prettyprint-override"><code>  var user = await User.find({uid: uid}) // user is found, as expected
    user[0].routes.push(route //parameter)  
    user.save()   
  </code></pre>
  <p>When a POST request is made, though, it throws an error:</p>
  <blockquote>
  <p>TypeError: user.save is not a function</p>
  </blockquote>
  <p>What am I doing wrong?</p>