Does MongoDB's $in clause guarantee order

Question

When using MongoDB\'s $in clause, does the order of the returned documents always correspond to the order of the array argument?

Answer 1

An easy way to order the result after mongo returns the array is to make an object with id as keys and then map over the given _id's to return an array that is correctly ordered.

async function batchUsers(Users, keys) {
  const unorderedUsers = await Users.find({_id: {$in: keys}}).toArray()
  let obj = {}
  unorderedUsers.forEach(x => obj[x._id]=x)
  const ordered = keys.map(key => obj[key])
  return ordered
}