title: Mongodb sort by date
body: <p>I have a document with a field <code>_id</code> has type <code>ObjectId</code>, and a field <code>created_at</code> has type <code>Date</code>.</p>
  
  <p><code>_id</code> is of course increasing, and the value of <code>created_at</code> is current_date should be increasing. </p>
  
  <p>So my question is :</p>
  
  <ol>
  <li>Is there any chance that 2 documents, A and B, <code>A._id &gt; B._id</code>, but <code>A.created_at &lt; B.created_at</code>.</li>
  <li>How to keep <code>created_at</code> as precise as possible, so the order of <code>created_at</code> corresponds to <code>_id</code>.</li>
  </ol>