How to create a new field in a MONGODB collection using an existing field

[Bayes-T_N_A]

i want to create a new field named “index” from an existing field named “id” in my MongoDB collection.

This is how my documents looks:

{
  "_id": {
    "$oid": "6536e62e619aa9d8e2cc82f7"
  },
  "name": "Thomas Bayes",
  "bithplace": "Londres",
  "institution": "Universidad de Edimburgo",
  "topics": [
    "teología",
    "estadística bayesiana"
  ],
  "maininterest": "Estadística Bayesiana",
  "img": "https://live.staticflickr.com/65535/53272747904_a07cba4990_n.jpg",
  "id": "1",

}

I tried db.getCollection("stats").updateMany( { }, { $set: { "$index": "$id"}} )

But i get index = “$id”, not the value of the key id… can you help me to achieve that? thank you

[Jason_Tran]

@Bayes-T_N_A

I tried db.getCollection("stats").updateMany( { }, { $set: { "$index": "$id"}} )

Based off the sample document you provided, do you want to have the "index" field with a value of 1?

I tried something similar in my test environment, you can see below:

testdb> db.coll.find()
[
  {
    _id: ObjectId("6552da8f81ae04007d21a860"),
    name: 'Thomas Bayes',
    bithplace: 'Londres',
    institution: 'Universidad de Edimburgo',
    topics: [ 'teología', 'estadística bayesiana' ],
    maininterest: 'Estadística Bayesiana',
    img: 'https://live.staticflickr.com/65535/53272747904_a07cba4990_n.jpg',
    id: '1' /// <--- id value of '1'
  }
]

Query and output:

/// Query
testdb> db.coll.updateMany( { }, [{ $set: { "index": "$id"}}] )
{
  acknowledged: true,
  insertedId: null,
  matchedCount: 1,
  modifiedCount: 1,
  upsertedCount: 0
}
/// Output
testdb> db.coll.find()
[
  {
    _id: ObjectId("6552da8f81ae04007d21a860"),
    name: 'Thomas Bayes',
    bithplace: 'Londres',
    institution: 'Universidad de Edimburgo',
    topics: [ 'teología', 'estadística bayesiana' ],
    maininterest: 'Estadística Bayesiana',
    img: 'https://live.staticflickr.com/65535/53272747904_a07cba4990_n.jpg',
    id: '1',
    index: '1' /// <--- index field now exists with a value of '1'
  }
]

See if this works for your use case and requirements on a test environment first before trying this out on production.

Regards,
Jason