Find ObjectId _id but Schema has defined _id as String

Question

Previously I didn't declare the _id in my Schema, so each new submission naturally will have MongoDB generated ObjectId as it's _id. However, the requirements have changed and now _id is declared as String as below.

var mongoose = require("mongoose");
var Schema = mongoose.Schema;

var MySchema = new Schema({
    _id: {
        type: String,
    },
    schoolID: {
        type: mongoose.Schema.Types.ObjectId, ref: 'School'
    },
    points: {
        type: Number
    },
});
MySchema.index({ schoolID : 1})

module.exports = mongoose.model('Submission', MySchema);

However, now I cannot find my previously inserted documents using _id at all. I tried

var submissionId = "60654319a8062f684ac8fde4"
Submission.findOne({ _id: mongoose.mongo.ObjectId(submissionId ) })
Submission.findOne({ _id: mongoose.Types.ObjectId(submissionId ) })
Submission.findOne({ _id: mongoose.ObjectId(submissionId ) })

but it will always return null. So when I use var mongoose = require('mongoose').set('debug', true); to check, it will display below; that all my queries above will still find using String, and not ObjectId

Mongoose: submission.findOne({ _id: '60654319a8062f684ac8fde4' }, { projection: {} })

Answer 1

Problem - _id: { type: String,}, mongoose will cast the value before making a query to the database, so in your case, it will always be a string.

Option -1

Convert your old objectId's to String as you're planning to use String _id so it's better to keep it consistent.

Run these commands from the shell, Robomongo

This will add records with strings _id for existing ObjectId records.

db.collection.find({}).toArray() // loop all records
    .forEach(function (c) {
        if (typeof c._id !== 'string') { // check _id is not string
            c._id = c._id.str; db.collection.save(c); // create new record with _id as string value
        }
    });

Delete records with ObjectId

db.collection.remove({ _id: { $type: 'objectId' } })

---

Option -2

Add Mongoose custom types.

https://mongoosejs.com/docs/customschematypes.html

class StringOrObjectId extends mongoose.SchemaType {
  constructor(key, options) {
    super(key, options, 'StringOrObjectId');
  }

  convertToObjectId(v) {
    const checkForHexRegExp = new RegExp("^[0-9a-fA-F]{24}$");
    let _val;
    try {
      if (checkForHexRegExp.test(v)) {
        _val = mongoose.Types.ObjectId(v);
        return _val;
      }
    } catch (e) {
      console.log(e);
    }
  }

  convertToString(v) {
    let _val = v;
    try {
      if(_.isString(_val)) return _val;
      if(_.isNumber(_val)) return _.toString(_val);
    } catch (e) {
      console.log(e);
    }
  }

  cast(val) {
    const objectIdVal = this.convertToObjectId(val);
    if (objectIdVal) return objectIdVal;

    const stringVal = this.convertToString(val)
    if (stringVal) return stringVal;

    throw new Error('StringOrObjectId: ' + val +
        ' Nor string nor ObjectId');
  }
}

mongoose.Schema.Types.StringOrObjectId = StringOrObjectId;

---

var MySchema = new Schema({
    _id: {
        type: StringOrObjectId, // custom type here
    },
    schoolID: {
        type: mongoose.Schema.Types.ObjectId, ref: 'School'
    },
    points: {
        type: Number
    },
});

---

Query

Submission.findOne({ _id: submissionId }); // it will cast ObjectId or String or throw error

---

Drawbacks

• If your _id type string is 60516ae1ef682d2804a2fa72 is like valid ObjectId it will convert to ObjectId which will not match the record.

Note - It's a rough class StringOrObjectId add proper checks and test properly.

---

Option -3

Easy way - Use mongoose.Mixed https://mongoosejs.com/docs/schematypes.html#mixed

https://mongoosejs.com/docs/api.html#mongoose_Mongoose-Mixed

cont MySchema = new Schema({
    _id: {
        type: mongoose.Mixed,
    },
    schoolID: {
        type: mongoose.Schema.Types.ObjectId, ref: 'School'
    },
    points: {
        type: Number
    },
});