我如何断言泛型类型 T 具有特定属性

Question

I am creating an abstract class BaseRepository which extends Repository . T is passed into this abstract class. The method main takes a partial of T but id should be an optional prop of T. How can I assert T to have optional prop id ?

export abstract class BaseRepository<T> extends Repository<T> {
  async main (changes: DeepPartial<T & { id?: number }>) {
    const p = this.create()
    Object.assign(p, changes)
    if (p && p.id) await this.update(p.id, p )
    const v = await this.save(p)
    return this.findOneOrFail({ where: v })
  }
}

Answer 1

Asserting that the generic type has an optional property is pretty simple. Just define an interface that has the property and say that the type extends that interface. This would look something like

interface Identifiable {
  id: number;
}

export abstract class BaseRepository<T extends Identifiable> extends Repository<T> {
  async main (changes: DeepPartial<T>) {
    const p = this.create();
    Object.assign(p, changes);

    if (p && p.id) {
      await this.update(p.id, p);
    }

    const v = await this.save(p);
    return this.findOneOrFail({ where: v })
  }
}