Loopback 4/MongoDB - Foreign key not converted to ObjectID

Question

I am trying to set up an hasMany relation using a Mongo database. I have followed the guide to create an hasMany relation in the loopback 4 documentation (https://loopback.io/doc/en/lb4/HasMany-relation.html) and tryied to set differents properties but the foreign key custId is saved as a string and not as an ObjectID.

I also found a few other properties or options from others topics but people were using Loopback 3 and it doesn't seem to work with Loopback 4.

Did I miss something or is there any workaround ?

Here are my models :

@model()
export class Order extends Entity {
  @property({
    type: 'string',
    id: true,
    generated: true,
  })
  id: string;

  @property({
    type: 'array',
    itemType: 'string',
    required: true,
  })
  product: string[];

  @property({
    type: 'number',
    required: true,
  })
  price: number;

  @property({
    type: 'string',
    id: true,
    generated: true,
  })
  custId: string;

  constructor(data?: Partial<Order>) {
    super(data);
  }
}


@model()
export class Customer extends Entity {
   @property({
      type: 'string',
      id: true,
      generated: true,
   })
   id: string;

   @property({
    type: 'string',
    required: true,
  })
  name: string;

  @property({
    type: 'string',
  })
  adress?: string;

  @hasMany(() => Order, {keyTo: 'custId'})
    orders?: Order[];

  constructor(data?: Partial<Customer>) {
    super(data);
  }
}

Answer 1

This is currently a bug. The hasMany / belongsTo will end up saving the relation id as a string instead of an ObjectId. You can verify this by changing the id in the database directly to an ObjectId and then it will find it.

Reference: https://github.com/strongloop/loopback-next/issues/2085

It is also mentioned on the latest Monthly Milestone here, so hopefully it will be resolved soon: https://github.com/strongloop/loopback-next/issues/2313

Edit: I was able to get it working by adding strictObjectIDCoercion to the model, but that can break other things according to issue 2085 linked above.

@model({
  settings: {
    strictObjectIDCoercion: true,
  }
})