MongoDb how change id of document to diffrent - mongodb

Question

Hello how to change an id of document to diffrent when some ids are equal?
I want to change some of employees id_director to object id thats is equal to id_director. I mean for example, when some document have id_director = 100 then changed it to _id with value of employee where id_employee = 100.
I was trying like this:
var employes = db.employees.find({"id_director": {$ne: null}});
while (employes.hasNext()) {
emp = employes.next();
employe = db.employees.findOne({"id_director":emp.id_employe});
emp.id_director = employe._id
db.employees.save(emp)
}
For example
I have two documents in one collection:
employees
{
"_id" : ObjectId("6224a5767b9cdbdcb681b1ef"),
"id_employe" : 180,
"id_director" : 100,
"name" : "Mark"
}
{
"_id" : ObjectId("6224a5767b9cdbdcb681b1f0"),
"id_employe" : 100,
"id_director" : null,
"name" : "Peter"
}
Expected document:
{
"_id" : ObjectId("6224a5767b9cdbdcb681b1ef"),
"id_employe" : 180,
"id_director" : ObjectId("6224a5767b9cdbdcb681b1f0"),
"name" : "Mark"
}

Answer 1

first of all you need to have peter's id then update mark document:
var peter= db.employees.findOne({_id: peterId});
db.employees.updateOne({
_id: markId
}, {
$set: {
id_director: peter._id
}
})

Answer 2

You can perform a self $lookup to lookup for the director_id, then perform some wrangling and $merge back to the collection.
db.collection.aggregate([
{
"$match": {
"id_director": {
$ne: null
}
}
},
{
"$lookup": {
"from": "collection",
"localField": "id_director",
"foreignField": "id_employe",
pipeline: [
{
"$limit": 1
},
{
$project: {
_id: 1
}
}
],
"as": "id_director"
}
},
{
$unwind: "$id_director"
},
{
$project: {
_id: 1,
id_employe: 1,
id_director: "$id_director._id",
name: 1
}
},
{
"$merge": {
"into": "collection",
"on": "_id",
"whenMatched": "replace"
}
}
])
Here is the Mongo playground for your reference.