mimarcos/typeorm-polymorphic

Typeorm polymorphic concept used with nestjs

typeorm-polymorphic concept

This is a concept I've put together for decorated polymorphic values with typeorm. I've taken a lot of inspiration from laravel's eloquent.

This has worked for my use case however it might not for others. This is an example of how I've used it.

@Entity('users')
export class UserEntity {
  @PrimaryGeneratedColumn()
  id: number;

  @PolymorphicChildren(() => AdvertEntity, {
    eager: false,
  })
  adverts: AdvertEntity[];
}

Entity('merchants')
export class MerchantEntity {
  @PrimaryGeneratedColumn()
  id: number;

  @PolymorphicChildren(() => AdvertEntity, {
    eager: false,
  })
  adverts: AdvertEntity[];
}

@Entity('adverts') 
export class AdvertEntity implements PolymorphicChildInterface {
  @PolymorphicParent(() => [UserEntity, MerchantEntity])
  @Transform(
    (value: UserEntity | MerchantEntity) => ({
      ...value,
      type: value.constructor.name,
    }),
    {
      toPlainOnly: true,
    },
  )
  owner: UserEntity | MerchantEntity;

  @Column()
  entityId: number;

  @Column()
  entityType: string;
}

This will result in the adverts table having values

==========================
id | entityId | entityType
==========================
 1 | 1        | 'UserEntity'
 2 | 1        | 'MerchantEntity'
 3 | 2        | 'UserEntity'

I think Perf might have some suggestions on how to improve things (sorry I have replied been mega busy!)

I've also used the class-transformer package so that my response objects have a different type value depending on the entityType. Could use the field tbh

Nestjs

My methods work with basic hydration however the query builder needs some work. I've used a custom repository to handle all of the saving/updating/fetch. I only really use typeorm with nestjs hence I can use the repository anywhere in my project like so

@Module({
  imports: [
    TypeOrmModule.forFeature([
      AdvertEntity,
      AdvertRepository,
    ]),
  ],
  providers: [AdvertService, CategoryService, TagService, AdvertPolicy],
  exports: [TypeOrmModule, AdvertService],
})
export class AdvertModule {}

Where AdvertRepository extends the AbstractPolymorphicRepository

@EntityRepository(AdvertEntity)
export class AdvertRepository extends AbstractPolymorphicRepository<
  AdvertEntity
> {
...

Now whenever I call advertRepository.findOne(1) it'll also find the advert's parent (UserEntity | MerchantEntity). Same with saving

advertRepository.save({
   owner: user,
});

Will automatically save the owner relationship. However this does depend on the user being an instanced UserEntity and not an object.

Possible use case

It is possible to have multiple types for both parent + children however I've not tested this use case.

Improvements

• Dynamically add fields for entityType + entityId and make them configurable
• Build helpful query builder methods
• Add tests!
• Separate from nestjs