title: Mongoose Select Populated Data's Size
body: <p>In my blog model;</p>
  <pre><code>...
  user: {
      type: mongoose.Types.ObjectId,
      ref: 'users',
      required: true,
  },
  ...
  </code></pre>
  <p>And this is my user model;</p>
  <pre><code>follower: [
      {
        type: mongoose.Types.ObjectId,
        ref: 'users'
      }
  ],
  </code></pre>
  <p>So I'm gettting data like this;</p>
  <pre><code>const Post = await Blog.findOne({slug: post}).populate({
        path: 'user',
        select: 'name image count(follower)'
  })
  </code></pre>
  <p>Of course <code>count(follower)</code> not working. I want to get followers count, how can I do that?</p>