Add overwriteDiscriminatorKey to API docs for findOneAndUpdate(), updateOne(); and findOneAndUpdate() guide

[akhilkcg]

Prerequisites

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

Mongoose version

6.12.5

Node.js version

14.18.1

MongoDB server version

3.6.6

Typescript version (if applicable)

No response

Description

In 5.x findOneAndUpdate successfully updates the value of a discriminatorKey field. However, in 6.x it does not

Steps to Reproduce

Repro script:

const mongoose = require('mongoose')
const Schema = mongoose.Schema

const superheroSchema = new Schema({
  name: { type: String },
  universe: { type: String }
}, { discriminatorKey: 'powerType' })

const Superhero = mongoose.model('Superhero', superheroSchema)
Superhero.discriminator('Money', new Schema({ money: { type: Number } }), { clone: false })
Superhero.discriminator('Strength', new Schema({ strength: { type: Number } }), { clone: false })

async function run() {
  await mongoose.connect('mongodb://localhost:27017');

  const doc = new Superhero({ name: 'Batman', universe: 'DC', powerType: 'Money', money: 100 });
  await doc.save()

  const updatedDoc = await Superhero.findOneAndUpdate({_id: doc._id}, { powerType: 'Strength' }, { new: true })
  console.log('new powerType:', updatedDoc.powerType)

  await mongoose.disconnect();
}

run()

Expected Behavior

Output in 5.12.5

new powerType: Strength

Output in 6.12.5

new powerType: Money

6.x must behave like 5.x

[vkarpov15]

This is intentional behavior; starting in Mongoose 6 you need to set the overwriteDiscriminatorKey option to modify the discriminator key in an update as described here: https://mongoosejs.com/docs/6.x/docs/discriminators.html#updating-the-discriminator-key

[akhilkcg]

thanks @vkarpov15