Update all documents in a collection in Mongodb with a new field

Question

I have a collection named employees with documents like.

{
first_name:"john",
last_name:"doe"
}

I want to run an update query which adds a new field like {name:'john doe'}

I know it can be done like this

db.employees.find({}).forEach(doc=>db.employees.update({"_id":doc._id},{$set:{name:doc.first_name+"-"+doc.last_name}}))

but its taking a lot of time when i am using mongo compass with db running in atlas.

Answer 1

Here's one way you could do it by using an update aggregation pipeline.

db.employees.update({
  "first_name": {"$exists": true},
  "last_name": {"$exists": true},
  "name": {"$exists": false}
},
[
  {
    "$set": {
      "name": {
        "$concat": ["$first_name", " ", "$last_name"]
      }
    }
  }
],
{"multi": true}
)

Try it on mongoplayground.net.