title: Get latest MongoDB record by field of datetime
body: <p>I have a collection like this:</p>
  
  <pre><code>{
      'datetime': some-date,
      'lat': '32.00',
      'lon': '74.00'
  },
  {
      'datetime': some-date,
      'lat': '32.00',
      'lon': '74.00'
  }
  </code></pre>
  
  <p>How can I get the latest record from MongoDB, where the datetime is the latest one? I want only a single record.</p>