typeorm-polymorphic
An extension package for polymorphic relationship management, declaration and repository queries for typeorm
Experiemental package
Install
$ yarn add typeorm-polymorphicYou'll also require
typeormandreflect-metadataif you haven't already installed these
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.
Extend the PolymorphicRepository
@EntityRepository(AdvertEntity)
export class AdvertRepository extends AbstractPolymorphicRepository<
AdvertEntity
> {}The below decorators will only work when using the above abstract repository AbstractPolymorphicRepository
Setup the entities
This is an example of one child, 2 parent types
Parents
@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[];
}Children
@Entity('adverts')
export class AdvertEntity implements PolymorphicChildInterface {
@PolymorphicParent(() => [UserEntity, MerchantEntity])
owner: UserEntity | MerchantEntity;
@Column()
entityId: number;
@Column()
entityType: string;
}Resulting values
This will result in the adverts table having values
adverts table
==========================
id | entityId | entityType
==========================
1 | 1 | 'UserEntity'
2 | 1 | 'MerchantEntity'
3 | 2 | 'UserEntity'
Decorators
Both PolymorphicChildren and PolymophicParent are treated same. Currently some of the default values are different but eventually these method should be synonyms of one another. They have different names because it helped me describe the relationship directions which could be explained as 'parent' 'child' in different ways.
Ambiguous direction
Both PolymorphicParent and PolymorphicChildren accepts either an array of types or a singular type
@PolymorphicChildren(() => [ChildEntity, AnotherChildEntity])
@PolymorphicParent(() => [ParentEntity, AnotherParentEntity])
@PolymorphicChildren(() => ChildEntity)
@PolymorphicParent(() => ParentEntity)Options
| key | what's it for? | default |
|---|---|---|
| eager | load relationships by default | true |
| cascade | save/delete parent/children on save/delete | true |
| deleteBeforeUpdate | delete relation/relations before update | false |
| hasMany | should return as array? | true for child. false for parent |
hasMany should really be updated so both parent and child declaration are the same. I've done to hopefully avoid confusion from the names!
Repository Methods
The majority of these methods overwrite the typeorm's Repository class methods to ensure polymorph relationships are handled before/after the parent's method.
save
Saves the given entity and it's parent or children
extends typeorm's Repository.save method
Child
const repository = connection.getRepository(AdvertRepository); // That extends AbstractPolymorphicRepository
const advert = new AdvertEntity();
advert.owner = user;
await repository.save(advert);Parent
const repository = connection.getRepository(MerchantRepository); // That extends AbstractPolymorphicRepository
const advert = new AdvertEntity();
const merchant = new MerchantEntity();
merchant.adverts = [advert];
await repository.save(merchant);find
extends typeorm's Repository.find method
const repository = connection.getRepository(MerchantRepository); // That extends AbstractPolymorphicRepository
const results = await repository.find();
// results[0].adverts === AdvertEntity[]findOne
extends typeorm's Repository.findOne method
create
This method creates the parent or child relations for you so you don't have to manally supply an array of classes.
extends typeorm's Repository.create method
Child
const repository = connection.getRepository(AdvertRepository); // That extends AbstractPolymorphicRepository
const results = await repository.create({
owner: new UserEntity(), // or MerchantEntity()
});Parent
const repository = connection.getRepository(UserRepository); // That extends AbstractPolymorphicRepository
const results = await repository.create({
adverts: [
{
name: 'test',
},
{
name: 'test',
},
],
});
/**
* {
* adverts: [
* AdvertEntity{
* name: 'test',
* },
* AdvertEntity{
* name: 'test',
* },
* ],
* }
*/hydrateMany
Hydreate one entity and get their relations to parent/child
const repository = connection.getRepository(AdvertRepository); // That extends AbstractPolymorphicRepository
const adverts = await repository.find();
// eager to parent (user|merchant) is set to false
adverts[0].owner; // undefined
await repository.hydrateMany(adverts);
adverts[0].owner; // UserEntity | MerchantEntityhydrateOne
Hydreate one entity and get their relations to parent/child
const repository = connection.getRepository(AdvertRepository); // That extends AbstractPolymorphicRepository
const advert = await repository.findOne(1);
// eager to parent (user|merchant) is set to false
advert.owner; // undefined
await repository.hydrateOne(advert);
advert.owner; // UserEntity | MerchantEntityClass-transformer
We recommend if you're working with polymorphic relationships that you use class-transformers's Transform decorator to distinguish the different types on the frontend when returning your entities from a http call
@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;
}The owner property object's type property will now either be string value of UserEntity or MerchantEntity
Possible relations
Singular parent, different children
This is an example of having the need of different types of children for a singular parent type
class RestaurantEntity {
@PolymorphicChildren(() => [WaiterEntity, ChefEntity])
staff: (WaiterEntity | ChefEntity)[];
}
class WaiterEntity implements PolymorphicChildInterface {
@Column()
entityId: string;
@Column()
entityType: string;
@PolymorphicParent(() => RestaurantEntity)
restaurant: RestaurantEntity;
}
class ChefEntity implements PolymorphicChildInterface {
@Column()
entityId: string;
@Column()
entityType: string;
@PolymorphicParent(() => RestaurantEntity)
restaurant: RestaurantEntity;
}Singular child, different parent
This is an example of having the need of a singular child shared between different types of parents
class AdvertEntity implements PolymorphicChildInterface {
@PolymorphicParent(() => [UserEntity, MerchantEntity])
owner: UserEntity | MerchantEntity;
}
class MerchantEntity {
@PolymorphicChildren(() => AdvertEntity)
adverts: AdvertEntity[];
}
class UserEntity {
@PolymorphicChildren(() => AdvertEntity)
adverts: AdvertEntity[];
}Notes
I think Perf might have some suggestions on how to improve things (sorry I have replied been mega busy!)
Nestjs
If you're using nestjs, don't forgot to include your repository into the entities array in forFeature
@Module({
imports: [
TypeOrmModule.forFeature([
AdvertEntity,
AdvertRepository,
]),
],
providers: [AdvertService, CategoryService, TagService, AdvertPolicy],
exports: [TypeOrmModule, AdvertService],
})
export class AdvertModule {}