Convert ObjectID to String in mongo Aggregation

Question

I\'m in this scenario right now: I have a collection X:

{
  _id:ObjectId(\'56edbb4d5f084a51131dd4c6\'),
  userRef:ObjectId(\'56edbb4d5f084a51131dd4c6\'),
  seria         


        

Answer 1

Now you can try with $toString aggregation which simply converts ObjectId to string

db.collection.aggregate([
    { "$addFields": {
        "userRef": { "$toString": "$userRef" }
    }},
    { "$group": {
      "_id": { "$concat": ["$userRef", "-", "$serialNumber"] }
    }}
])

You can check the output here