Convert ObjectId to String in the MongoDB

Question

I have an aggregate query.

{ "$addFields": {
  "collegeID": (('$collegeDetail._id')),
}}

where, I want to add a new field 'CollegeID' as a string version of the ObjectId stored in collegeDetail._id.

Any help will be appreciated. Thanks.

This is not currently supported, but will be available in an upcoming release. See here. — Kirk Larkin
– Kirk Larkin, Commented May 30, 2018 at 17:03
I can't see anything out there - all solutions talk of doing it in the JavaScript context, outside of an aggregation pipeline, which I guess is not what you are looking for. — Kirk Larkin
– Kirk Larkin, Commented May 30, 2018 at 17:07

Ashh · Accepted Answer · 2018-12-09 08:44:10Z

4

You should try $toString aggregation to convert ObjectId to string

db.strcoll.aggregate([
  { "$addFields": {
    "collegeID": { "$toString": "$collegeDetail._id" }
  }}
])

edited Dec 9, 2018 at 8:44

answered May 30, 2018 at 17:24

Ashh

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Comments

iatsi · Accepted Answer · 2018-07-18 12:33:13Z

1

Edit: Starting from (Version 4.0 of MongoDB) Gladly MongoDB has made and update and got us a new operator that does this job.

$convert

This can be used to change the data type of value from almost each type to each type

For more information check it up here: https://docs.mongodb.com/manual/reference/operator/aggregation/convert/

Hope this helps;

answered Jul 18, 2018 at 12:33

iatsi

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Comments

Syed Ahsan Ali · Accepted Answer · 2018-10-25 01:43:23Z

1

The Link below will provide you javascript way to convert objectId to string: Convert ObjectID (Mongodb) to String in JavaScript

edited Oct 25, 2018 at 1:43

answered May 30, 2018 at 17:04

Syed Ahsan Ali

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1 Comment

iatsi Over a year ago

Thanks for the help, but as you see in the question I wanted to do it in the query itself.

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