mongodb command for mongoose populate code example

Example 1: how to use mongoose populate

function getUserWithPosts(username){  return User.findOne({ username: username })    .populate('posts').exec((err, posts) => {      console.log("Populated User " + posts);    })}

Example 2: how to use mongoose populate

{  _id: 59ab1c92ea84486fb4ba9f28,  username: JD,  posts: [    "59ab1b43ea84486fb4ba9ef0",    "59ab1b43ea84486fb4ba9ef1"  ]}