typeorm-polymorphic


An extension package for polymorphic relationship management, declaration and repository queries for typeorm

> Experiemental package

Install

``bash
$ yarn add typeorm-polymorphic
`

> You'll also require typeorm and reflect-metadata if 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.

$3

`ts
import { PolymorphicRepository } from 'typeorm-polymorphic';

@PolymorphicRepository(AdvertEntity)
export class AdvertRepository extends AbstractPolymorphicRepository<
AdvertEntity
> {}
`

Then, to instantiate your repository you can call:

`ts
import { AbstractPolymorphicRepository } from 'typeorm-polymorphic';

const repository = AbstractPolymorphicRepository.createRepository(
dataSource, // where dataSource is a typeorm DataSource object
AdvertRepository,
);
`

> The below decorators will only work when using the above abstract repository AbstractPolymorphicRepository

$3

This is an example of one child, 2 parent types

#### Parents

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

@PolymorphicChildren(() => AdvertEntity, {
eager: false,
})
adverts: AdvertEntity[];
}
`
`ts
Entity('merchants')
export class MerchantEntity {
@PrimaryGeneratedColumn()
id: number;

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

#### Children

`ts
@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 PolymorphicParent 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.

PolymorphicRepository allows you to define a custom typeorm repository and then
instantiate it later via AbstractPolymorphicRepository.createRepository(...).

$3

Both PolymorphicParent and PolymorphicChildren accepts either an array of types or a singular type

`ts
@PolymorphicChildren(() => [ChildEntity, AnotherChildEntity])
@PolymorphicParent(() => [ParentEntity, AnotherParentEntity])

@PolymorphicChildren(() => ChildEntity)
@PolymorphicParent(() => ParentEntity)
`

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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.

$3

Saves the given entity and it's parent or children

extends typeorm's Repository.save method

##### Child

`ts
const repository = connection.getRepository(AdvertRepository); // That extends AbstractPolymorphicRepository

const advert = new AdvertEntity();
advert.owner = user;

await repository.save(advert);
`

##### Parent

`ts
const repository = connection.getRepository(MerchantRepository); // That extends AbstractPolymorphicRepository

const advert = new AdvertEntity();

const merchant = new MerchantEntity();
merchant.adverts = [advert];

await repository.save(merchant);
`

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extends typeorm's Repository.find method

`ts
const repository = connection.getRepository(MerchantRepository); // That extends AbstractPolymorphicRepository

const results = await repository.find();

// results[0].adverts === AdvertEntity[]
`


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extends typeorm's Repository.findOne method




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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

`ts
const repository = connection.getRepository(AdvertRepository); // That extends AbstractPolymorphicRepository

const results = await repository.create({
owner: new UserEntity(), // or MerchantEntity()
});
`

##### Parent

`ts
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',
* },
* ],
* }
*/
`

$3

Hydreate one entity and get their relations to parent/child

`ts
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 | MerchantEntity
`

$3

Hydreate one entity and get their relations to parent/child

`ts
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 | MerchantEntity
`

Class-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

`ts
@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

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This is an example of having the need of different types of children for a singular parent type

`ts
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;
}

`

$3

This is an example of having the need of a singular child shared between different types of parents

`ts
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

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