title: Mongoose expiry
body: <p>I have the below schema:</p>
  
  <pre><code>ip: String,
  port: Number,
  msgboard: [{
     date: {
          type: Date,
          default: Date.now,
          expires: 120
          },
     msg: String
  }]
  </code></pre>
  
  <p>I want the messages to be removed automatically after 120s from creation. But the above delete's the whole document and not just that subdoc from msgboard.
  I have been doing it using cron and running a function, but the code seems too untidy. Is there any inbuilt way ?</p>