document.populate() throws an error when populating an array of immutable items

[ThoseGrapefruits]

Do you want to request a feature or report a bug?

Report a bug.

What is the current behavior?

When calling document.populate() with a path to an array whose elements are marked as immutable, Mongoose throws the following error:

/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/schema/array.js:392
        throw new CastError('[' + e.kind + ']', util.inspect(value), this.path + '.' + i, e, this);
              ^

CastError: Cast to [undefined] failed for value "["607dec18c3b1d8443014f1dc"]" at path "friends.0"
    at SchemaArray.cast (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/schema/array.js:392:15)
    at convertTo_id (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/helpers/populate/getModelsMapForPopulate.js:515:28)
    at getModelsMapForPopulate (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/helpers/populate/getModelsMapForPopulate.js:242:13)
    at populate (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/model.js:4364:21)
    at _populate (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/model.js:4335:5)
    at /Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/model.js:4312:5
    at promiseOrCallback (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/helpers/promiseOrCallback.js:9:12)
    at Mongoose._promiseOrCallback (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/index.js:1154:10)
    at Function.Model.populate (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/model.js:4310:23)
    at model.populate (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/document.js:3917:19)
    at /Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/document.js:3989:10
    at /Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/helpers/promiseOrCallback.js:31:5
    at new Promise (<anonymous>)
    at promiseOrCallback (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/helpers/promiseOrCallback.js:30:10)
    at model.Document.execPopulate (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/document.js:3988:10)
    at file:///Users/thosegrapefruits/Desktop/populate-immutable-array.mjs:23:33 {
  stringValue: '"["607dec18c3b1d8443014f1dc"]"',
  messageFormat: undefined,
  kind: '[undefined]',
  value: '["607dec18c3b1d8443014f1dc"]',
  path: 'friends.0',
  reason: TypeError: Invalid `path`. Must be either string or array
      at Object.exports.get (/Users/thosegrapefruits/Desktop/node_modules/mpath/lib/index.js:59:11)
      at Object.exports.getValue (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/utils.js:596:16)
      at model.Document.$__getValue (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/document.js:1558:16)
      at model.immutableSetter (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/helpers/schematype/handleImmutable.js:37:25)
      at ObjectId.SchemaType._applySetters (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/schematype.js:1075:16)
      at ObjectId.SchemaType.applySetters (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/schematype.js:1099:16)
      at SchemaArray.cast (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/schema/array.js:388:29)
      at convertTo_id (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/helpers/populate/getModelsMapForPopulate.js:515:28)
      at getModelsMapForPopulate (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/helpers/populate/getModelsMapForPopulate.js:242:13)
      at populate (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/model.js:4364:21)
      at _populate (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/model.js:4335:5)
      at /Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/model.js:4312:5
      at promiseOrCallback (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/helpers/promiseOrCallback.js:9:12)
      at Mongoose._promiseOrCallback (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/index.js:1154:10)
      at Function.Model.populate (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/model.js:4310:23)
      at model.populate (/Users/thosegrapefruits/Desktop/node_modules/mongoose/lib/document.js:3917:19)
}

If the current behavior is a bug, please provide the steps to reproduce.

Repro script. Using module syntax, save in something.mjs and it should run fine w/ node.

import mongoose from 'mongoose';

mongoose.connect('mongodb://localhost:27017/cats', {
  useNewUrlParser: true, useUnifiedTopology: true
});

const Cat = mongoose.model('Cat', {
  name: String, 

  friends: [ {
    immutable: true,
    type: mongoose.ObjectId,
    ref: 'Cat'
  } ]

  // Note that the following works fine, but the per-array-item immutability is
  // still desired because otherwise you can do cat.friends[0] = someOtherCatId

  // friends: {
  //   immutable: true,
  //   type: [ {
  //     type: mongoose.ObjectId,
  //     ref: 'Cat'
  //   } ],
  // }
});

const friend = new Cat({ name: 'Zildjian' });
await friend.save();

const myCat = new Cat({ name: 'Lord Fluffles', friends: [ friend.id ] })
await myCat.save();

await myCat.populate('friends').execPopulate();

What is the expected behavior?

The field's array elements should be populated, and no error should be thrown.

What are the versions of Node.js, Mongoose and MongoDB you are using? Note that "latest" is not a version.

Node: 15.14.0
Mongoose: 5.12.5 (but it seems to have broken in 5.11.10, as 5.11.9 is the last version where this worked fine)
MongoDB: 4.2.11

[IslandRhythms]

Not the same error but it is giving an error:

const mongoose = require('mongoose');

const Cat = mongoose.model('Cat', {
    name: String,
    friends: [{
        immutable: true,
        type: mongoose.isValidObjectId,
        ref: 'Cat'
    }]
});

async function run() {
    await mongoose.connect('mongodb://localhost:27017/test', {
        useNewUrlParser: true,
        useUnifiedTopology: true
      });
    
    await mongoose.connection.dropDatabase();

    const friend = new Cat({name: 'Zildjian'});
    await friend.save();
    const myCat = new Cat({name: 'Lord FLuffles', friends: [friend.id]});
    await myCat.save();
    await myCat.populate('friends').execPopulate();
}

run();

[ThoseGrapefruits]

Oh, I think in your script, the line

type: mongoose.isValidObjectId

should be

type: mongoose.Types.ObjectId

With that, it throws what looks to be the same error as mine.

[IslandRhythms]

Yup. that was it. Thank you.

[ThoseGrapefruits]

Thanks for the quick turnaround @vkarpov15 !