RawDocType is not accessible trought toObject/toJSON transform function anymore

[PedroLucasHablla]

Prerequisites

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

Mongoose version

8.16.2

Node.js version

22.16.0

MongoDB server version

7.0.21 Atlas

Typescript version (if applicable)

No response

Description

The #15501 PR introduced the ability to retrieve the _id and __v of a document from the ret parameter of the toObject/toJSON transform function. However, by doing so, the RawDocType is no longer accessible through the ret parameter, leading to a series of compilation errors when trying to access a document property, such as:

Steps to Reproduce

Try to access any document property over the ret parameter in the transform() function.

Expected Behavior

No response

[vkarpov15]

The fact that your RawDocType only has _id: unknown is concerning, can you please provide a more complete repro script? For example, the following triggers a similar error:

import mongoose from 'mongoose';

const { Schema } = mongoose;

const schema = new Schema({
  name: { type: String, required: true }
}, {
  toObject: {
    transform(doc, ret) {
      ret.id = ret._id?.toString();
    }
  }
});
const TestModel = mongoose.model('Test', schema);

However the type is more correct in the error message: error TS2339: Property 'id' does not exist on type 'FlatRecord<{ name: string; }> & { _id: ObjectId; } & { __v: number; }'.

The only way Mongoose could fix the error in the above would be to once again make ret resolve to any. Otherwise, this is expected behavior in TypeScript: you can't assign arbitrary properties to objects. The more TypeScript-friendly approach is returning a new object as follows:

const schema = new Schema({
  name: { type: String, required: true }
}, {
  toObject: {
    transform(doc, ret) {
      return { ...ret, id: ret._id.toString() };
    }
  }
});

[PedroLucasHablla]

Thank you for the fast answer! It turns out that this was my fault from the beginning.

I didn't mentioned, but I'm using mongoose through NestJS. Here we define schemas by using decorators like this:

@Schema({
  toJSON: {
    getters: true,
    virtuals: true,
    transform(doc, ret: any) {
      ret.workspace_id = ret.workspace?.toString() // was working on 8.13.2
      ret.id = ret._id?.toString(); // was working on 8.13.2
      ret.id = String(ret._id);
      delete ret._id;
      delete ret.__v;
    },
  },
  timestamps: { createdAt: 'created_at', updatedAt: 'updated_at' },
})
export class Test {
  @Transform(({ value }) => value.toString())
  _id?: ObjectId;

  id?: string;

  @Prop({ type: MongooseSchema.Types.ObjectId, ref: 'Workspace' })
  workspace?: Workspace;

  @Prop({ type: String, required: true })
  name?: string;
}

What was going on is that when I declared the tranform() function, I didn't set the ret parameter as any in some of my schemas, that what was causing the compilation error on my end. This problem was not happening before 8.16.2, that's why I thought that was a mongoose problem. That's just probably something weird happening on @nestjs/mongoose side.

Any way, thank you so much for the time answering this issue. I'll close it, but I'm happy to help if you'd like to investigate this further.