Update id in mongodb collection

Question

Hello im learning MongoDB and my exercise is to update id in one of my collection to another id. I Have two collection

First collection "workers" :

{
    "_id" : ObjectId("6224ec342c2d7202b9ad9af6"),
    "id_worker" : 180,
    "id_boss" : 100,
    "hired" : ISODate("2005-02-20T00:00:00Z"),
    "id_group" : 10
}

Second collection "groups":

{
    "_id" : ObjectId("6224ebe12c2d7202b9ad9af1"),
    "id_group" : 10,
    "name" : "Administrators",
    "addres" : "Example"
}

I would like to change an "_id" of my worker to its "identifiaction id" from collection "groups"

So my worker should look like:

{
    "_id" : ObjectId("6224ec342c2d7202b9ad9af6"),
    "id_worker" : 180,
    "id_boss" : 100,
    "hired" : ISODate("2005-02-20T00:00:00Z"),
    "id_group" : ObjectId("6224ebe12c2d7202b9ad9af1")
}

I have query like this. When i use print it shows list of my workers with name of the group. How to change it to modify this collection? use update?

var workers = db.workers.find();
while (workers.hasNext()) {
worker = workers.next();
group = db.groups.findOne({"id_group": worker.id_group});
 print(group.name);
}

Answer 1

Try this:

db.workers.aggregate([
  {
    $lookup: {
      from: "groups",
      localField: "id_group",
      foreignField: "id_group",
      as: "group"
    }
  },
  {
    $project: {
      id_worker: 1,
      id_boss: 1,
      hired: 1,
      id_group: { $first: "$group.name" }
    }
  }
])

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