Bug: TypeError: Cannot read property 'name' of undefined at walkUpdatePath

[andreialecu]

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

Bug

What is the current behavior?

I ran into a weird issue while working with .bulkWrite(). I'm using nestjs and graphql and it appears that input objects coming in have a null prototype.

Here's an example via console.log of the update I'm attempting:

[
  {
    updateOne: {
      filter: { _id: '7b88d3a7-0044-4e2d-8190-3b833cd49bd8' },
      update: {
        '$set': {
          'units.1': [Object: null prototype] {
            clubId: 'f3700334708f5865',
            eventId: '75dedfaf9f7b68d1',
            kind: 'tournamentClock',
            layout: 'layout-1'
          }
        }
      }
    }
  }
]

Notice the [Object: null prototype]. This results in this error:

TypeError: Cannot read property 'name' of undefined
    at walkUpdatePath (mongoose/lib/helpers/query/castUpdate.js:203:32)
    at castUpdate (mongoose/lib/helpers/query/castUpdate.js:95:7)
    at mongoose/lib/helpers/model/castBulkWrite.js:73:37

The problem is on this line:

mongoose/lib/helpers/query/castUpdate.js

Line 203 in f1e0de1

if (val && val.constructor.name === 'Object') {

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

Repro:

const mongoose = require('mongoose');

mongoose.set('debug', true);

run().catch((err) => console.log(err));

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

  await mongoose.connection.dropDatabase();

  const schema = new mongoose.Schema(
    {
      _id: String,
      someArray: [
        new mongoose.Schema({ message: String }, { discriminatorKey: 'kind' }),
      ],
    },
    { timestamps: false },
  );
  schema.path('someArray').discriminator(
    'Foo',
    new mongoose.Schema({
      element: {
        type: String,
        required: true,
      },
    }),
  );

  schema.path('someArray').discriminator(
    'Bar',
    new mongoose.Schema({
      product: {
        type: String,
        required: true,
      },
    }),
  );

  const update = {
    updateOne: {
      filter: { _id: 'test' },
      update: {
        $set: {
          'someArray.1': {
            __proto__: null,
            kind: 'Foo',
            element: 'test',
          },
        },
      },
    },
  };

  console.dir(update, { depth: 5 });

  const Model = mongoose.model('MyModel', schema);
  await Model.bulkWrite([update]);

  console.log('Done');
}

What is the expected behavior?

I can work around it in my code by doing something like { ...objWithNullPrototype } instead, but this should probably not crash mongoose.

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

5.13.4