Is there a native way to ensure a document exists in database before creating a subdocument with NestJS/Mongo?

I'm writing a NestJS api using MongoDB (and Mongoose) for the database. I have a parent document: "Writer", which may have subdocuments: "Book".

Here is the "Writer" document:

import { Prop, Schema, SchemaFactory } from '@nestjs/mongoose';
import { Document } from 'mongoose';

export type WriterDocument = Writer & Document;

@Schema()
export class Writer {

  @Prop({
    required: [true, "Name is required and can't be empty!"],
    unique: true
  })
  name: string;

}

export const WriterSchema = SchemaFactory.createForClass(Writer);

And the "Book" subdocument:

import { Prop, Schema, SchemaFactory } from '@nestjs/mongoose';
import mongoose, { Document } from 'mongoose';
import { Writer } from 'src/writer/schemas/writer.schema';

export type BookDocument = Book & Document;

@Schema()
export class Book {

    @Prop({
        required: true,
        type: mongoose.Schema.Types.ObjectId,
        ref: Writer.name
    })
    writer: Writer;

    @Prop({ required: true })
    name: string;

}

export const BookSchema = SchemaFactory.createForClass(Book);

I want to ensure the writer exists before inserting any book for him in the database, but if I'm right, by default, the existence of the writer is not checked, and a book can be inserted at any time without having a real writer.

I just started using NestJS and MongoDB (with Mongoose), and I don't really know how to do it. Maybe this is the way to do with these technologies but I would rather prevent this from happening.

How can I do that? With Middleware? Guard? Pipe? Something else?

Thanks in advance.