title: how to get virtual fields in aggregation query in mongodb?
body: <p>i have model with one virtual field <code>show</code>:</p>
  
  <pre><code>modelSchema.virtual('show').get(function () {
      return true
  })
  </code></pre>
  
  <p>now, when I use query in nodeJS with <code>find</code> like this:</p>
  
  <pre><code>model.find({"$license_id": license_id})
  </code></pre>
  
  <p>In result, I have the virtual field <code>show</code>.</p>
  
  <p>but</p>
  
  <p>if I use query with <code>aggregation</code>  like this :</p>
  
  <pre><code>model.aggregate([
      {
          $match: {
              $expr: { $eq: ["$license_id", license_id] }
          }
      }
  ])
  </code></pre>
  
  <p>In result, I don't have the virtual field <code>show</code>.</p>
  
  <p>how to get the virtual fields in <code>aggregation</code> queries?
  Do you have any idea to solve this problem?</p>