TypeScript type for EntityDTO with ManyToOne field is not correct

[dzcpy]

Describe the bug
When JSONify entities which has unpopulated ManyToOne fields, the return result has wrong TypeScript types.

Stack trace

To Reproduce
Steps to reproduce the behavior:

1. Given the following entities:

@Entity()
export class TeamMember extends BaseEntity<TeamMember, 'id'> {
  @PrimaryKey({ type: 'uuid', defaultRaw: 'uuid_generate_v4()' })
  id: string;

  @ManyToOne({ entity: () => Team, onDelete: 'CASCADE', onUpdateIntegrity: 'CASCADE' })
  team: IdentifiedReference<Team>;
}

@Entity()
export class Team extends BaseEntity<Team, 'id'> {
  @PrimaryKey({ type: 'uuid', defaultRaw: 'uuid_generate_v4()' })
  id: string;

  @OneToMany({ entity: () => TeamMember, mappedBy: (teamMember) => teamMember.team, orphanRemoval: true, cascade: [Cascade.ALL] })
  members = new Collection<TeamMember>(this);
}

2. Get the JSON verson of TeamMember record:

const teamMember = await orm.em.findOne(TeamMember, '{actual-team-member-id}');
const teamMemberJSON: EntityDTO<TeamMember> = teamMember.toJSON();
console.log(teamMemberJSON.team);
// 022b5aab-4a04-4c86-a9f0-e6c9748a7f74

teamMemberJSON.team's type now should be EntityDTO<Team>, but actually, it's a string id. So it causes some type errors

Expected behavior
Either set unpopulatd ManyToOne fields of JSONified object to string, or something like team: { id: '{actual-id}' };

Additional context

Versions

Dependency	Version
node	17
typescript	4.4.4
mikro-orm	5.0.0-dev.439
your-driver	postgresql

[B4nan]

It can be PK or an object, depending of if you populate it. This information is available on the Loaded type, so even if we would have the EntityDTO type supporting it, you would basically erase it by explicitly defining your teamMemberJSON variable type (here it does not matter as you are not populating the relation).

Don't expec too much magic, those types will be always a bit wonky as we don't have the full context in many places. But in this particular example I hope we can handle it.

edit: Actually this might be problematic too, as I don't see a way to make the toJSON and others respect the Loaded context (this is Loaded but this.toJSON() won't pass the Loaded type to the EntityDTO, just the raw entity type). Seems like the problem is with the base entity, without it at least we see the type as EntityDTO<Loaded<...>>.

[B4nan]

This will be finally resolved with the TS 4.8 update, including the inference for base entity methods. It will be slightly breaking (on type level) release for those who define custom toJSON methods - the signature will need to return EntityDTO<this> instead of EntityDTO<User> etc.