title: How to duplicate a record/document in MongoDB?
body: <p>I want to duplicate my document based on a field in MongoDB.
  Refer to this documents below:
  <code>
  a:1,b:2,c:3,
  a:2,b:2,c:3,
  a:1,b:4,c:3,
  a:2,b:2,c:3,
  a:1,b:5,c:6
  </code>
  So, i want duplicates of the documents where a=1.</p>
  
  <p>Output should be like this:
  <code>
  a:1,b:2,c:3,
  a:2,b:2,c:3,
  a:1,b:4,c:3,
  a:2,b:2,c:3,
  a:1,b:5,c:6,
  a:1,b:2,c:3,
  a:1,b:4,c:3,
  a:1,b:5,c:6
  </code></p>