Model.bulkWrite updateOne fails to update discriminator key with overwriteDiscriminatorKey set to true

[lcrosetto]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Mongoose version

8.8.1

Node.js version

20.18.0

MongoDB server version

8.0.1

Typescript version (if applicable)

No response

Description

When updating the discriminator key in a document with schema discriminators, and setting the overwriteDiscriminatorKey option, the update succeeds when done with Model.updateOne() but fails when the same update is done by calling Model.bulkWrite() with the updateOne op.

Steps to Reproduce

The following script will fail to update the discriminator key:

      const conn = mongoose.createConnection(..);

      const dSchema1 = new mongoose.Schema({
        field1: String,
      });
      const dSchema2 = new mongoose.Schema({
        field2: String,
      });
      const baseSchema = new mongoose.Schema({
        field: String,
        key: String,
      }, {discriminatorKey: 'key'});
      const type1Key = 'Type1';
      const type2Key = 'Type2';

      baseSchema.discriminator(type1Key, dSchema1);
      baseSchema.discriminator(type2Key, dSchema2);

      const TestModel = conn.model('Test', baseSchema);

      const test = new TestModel({
        field: 'base field',
        key: type1Key,
        field1: 'field1',
      });
      const r1 = await test.save();
      assert.equal(r1.field1, 'field1');
      assert.equal(r1.key, type1Key);

      const field2 = 'field2';
      await TestModel.bulkWrite([{
        updateOne: {
          filter: { _id: r1._id },
          update: {
            key: type2Key,
            field2,
          },
          overwriteDiscriminatorKey: true,
        },
      }]);

      const r2 = await TestModel.findById(r1._id);
      assert.equal(r2.key, type2Key);
      assert.equal(r2.field2, field2);

      conn.deleteModel('Test');

However, if the call to bulkWrite() is replaced with updateOne() the operation will succeed:

      const field2 = 'field2';
      await TestModel.updateOne(
        { _id: r1._id },
        {
          key: type2Key,
          field2,
        },
        {overwriteDiscriminatorKey: true},
      );
      const r2 = await TestModel.findById(r1._id);
      assert.equal(r2.key, type2Key);
      assert.equal(r2.field2, field2);

Expected Behavior

Overwriting the discriminator key should succeed with Model.bulkWrite() as the same request does when done with Model.updateOne().

[lcrosetto]

I have gotten the overwriteDiscriminatorKey option to work with Model.bulkWrite() updateOne with the following changes:

mongoose/lib/helpers/model/castBulkWrite.js

Lines 104 to 108 in f450083

	op['updateOne']['update'] = castUpdate(model.schema, update, {
	strict: strict,
	upsert: op['updateOne'].upsert,
	arrayFilters: op['updateOne'].arrayFilters
	}, model, op['updateOne']['filter']);

        op['updateOne']['update'] = castUpdate(model.schema, update, {
          strict: strict,
          upsert: op['updateOne'].upsert,
          arrayFilters: op['updateOne'].arrayFilters,
          overwriteDiscriminatorKey: op['updateOne'].overwriteDiscriminatorKey
        }, model, op['updateOne']['filter']);

mongoose/lib/helpers/model/castBulkWrite.js

Lines 64 to 70 in f450083

	const model = decideModelByObject(originalModel, op['updateOne']['filter']);
	const schema = model.schema;
	const strict = options.strict != null ? options.strict : model.schema.options.strict;
	const update = clone(op['updateOne']['update']);
	_addDiscriminatorToObject(schema, op['updateOne']['filter']);

        const update = clone(op['updateOne']['update']);
        const {overwriteDiscriminatorKey} = op['updateOne'];

        const model = decideModelByObject(originalModel, update, op['updateOne']['filter'], {overwriteDiscriminatorKey});
        const schema = model.schema;
        const strict = options.strict != null ? options.strict : model.schema.options.strict;
        const {discriminatorKey} = schema.options;


        if (discriminatorKey && (!overwriteDiscriminatorKey || update[discriminatorKey] == null)) {
          _addDiscriminatorToObject(schema, op['updateOne']['filter']);
        }

mongoose/lib/helpers/model/castBulkWrite.js

Lines 275 to 281 in f450083

	function decideModelByObject(model, object) {
	const discriminatorKey = model.schema.options.discriminatorKey;
	if (object != null && object.hasOwnProperty(discriminatorKey)) {
	model = getDiscriminatorByValue(model.discriminators, object[discriminatorKey]) || model;
	}
	return model;
	}

function decideModelByObject(model, object, filter, options) {
  const discriminatorKey = model.schema.options.discriminatorKey;
  let key;
  if (options?.overwriteDiscriminatorKey && object?.[discriminatorKey] != null && model.discriminators) {
    key = object[discriminatorKey];
  } else if (filter != null && filter.hasOwnProperty(discriminatorKey)) {
    key = filter[discriminatorKey];
  }
  if (key) model = getDiscriminatorByValue(model.discriminators, key) || model;
  return model;
}

Changes may be needed for other ops as well.

[lcrosetto]

The above changes determine the schema in a similar way to query._castUpdate()