How to add nested array of objects with @Prop decorator from @nestjs/mongoose

Question

When I use a nested array of object in prop decorator:

@Schema()
export class Child {
  @Prop()
  name: string;
}
    
@Schema()
export class Parent {
  @Prop({type: [Child], _id: false}) // don't need `_id` for nested objects
  children: Child[];
}

export const ParentSchema = SchemaFactory.createForClass(Parent);

I get an error:

TypeError: Invalid schema configuration: `Child` is not a valid type within the array `children`.

How can I fix this if I need to use @Prop({_id: false}) (to keep the nested schema independent)?

---

If we change a prop decorator to @Prop([Child]) it works, however we need to disable _id for nested object with:

@Schema({_id: false})
export class Child {
  @Prop()
  name: string;
}

@Schema()
export class Parent {
  @Prop([Child])
  children: Child[];
}

And in this case we won't have generic Child object and we won't to use them as an independent Schema.

Another way is to create Child schema and use it in @Prop({type: [childSchema], _id: false}) , but that looks like an overhead.

Answer 1

a quik example that describe your case is:

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

class GuildMember {
  @Prop({ type: String, required: true, lowercase: true })
  _id: string;

  @Prop({ required: true })
  id: number;

  @Prop({ required: true })
  rank: number;
}

@Schema({ timestamps: true })
export class Guild extends Document {
  @Prop({ type: String, required: true, lowercase: true })
  _id: string;

  @Prop({ type: MongooseSchema.Types.Array})
  members: GuildMember[]
}

export const GuildsSchema = SchemaFactory.createForClass(Guild);

because in nested schema you don't have yo define type INSIDE the prop decorator but only tell that this field is an array and validate the type using TypeScript