Model.updateOne() and arrayFilters fails to update embedded document array fields when overwriting embedded discriminator key

[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

8.8.2

Node.js version

20.18.0

MongoDB server version

8.0.1

Typescript version (if applicable)

No response

Description

When using Model.updateOne() and arrayFilters to overwrite the discriminator key in an embedded document array with schema discriminators (and setting the overwriteDiscriminatorKey option), the discriminator key is updated, but fields unique to the discriminator schema fail to be updated. I suspect this is a problem with determining the schema from the update object, possibly related to the getEmbeddedDiscriminatorPath() helper.

Steps to Reproduce

The following script will fail to update field2:

      const conn = mongoose.createConnection(..);

      const embedDiscriminatorSchema = new mongoose.Schema({
        field1: String,
      });
      const embedDiscriminatorSchema2 = new mongoose.Schema({
        field2: String,
      });
      const embedSchema = new mongoose.Schema({
        field: String,
        key: String,
      }, {discriminatorKey: 'key'});
      embedSchema.discriminator('Type1', embedDiscriminatorSchema);
      embedSchema.discriminator('Type2', embedDiscriminatorSchema2);

      const testSchema = new mongoose.Schema({
        testArray: [embedSchema],
      });

      const TestModel = conn.model('Test', testSchema);
      const test = new TestModel({
        testArray: [{
          key: 'Type1',
          field: 'field',
          field1: 'field1',
        }],
      });

      const r1 = await test.save();
      assert.equal(r1.testArray[0].field1, 'field1');

      const field2update = 'field2 update';
      await TestModel.updateOne(
        { _id: r1._id },
        {
          $set: {
            'testArray.$[element].key': 'Type2',
            'testArray.$[element].field2': field2update,
          },
        },
        {
          arrayFilters: [
            {
              'element._id': r1.testArray[0]._id,
            },
          ],
          overwriteDiscriminatorKey: true,
        },
      );

      const r2 = await TestModel.findById(r1._id);
      assert.equal(r2.testArray[0].key, 'Type2');
      assert.equal(r2.testArray[0].field2, field2update);

      conn.deleteModel('Test');

Expected Behavior

Model.updateOne() should update the fields from the discriminator (key) set in the update, if overwriteDiscriminatorKey is set to true. Probably the schema would be found using the discriminator key in the update:

'testArray.$[element].key': 'Type2',