single table inheritance

Single Table Inheritance, or "STI" for short, is a design pattern which enables a single table to reflect multiple unique models, all of which inherit from a base model. In order for STI to work, a type field must be present on the STI model, like so:

export async function up(db: Kysely<any>): Promise<void> {
  await db.schema
    .createTable('pets')
    ...
    .addColumn('type', 'varchar(255)', col => col.notNull())
    ...
    .execute()
}

If desired, you can also use enums to enforce only specific types, like so:

export async function up(db: Kysely<any>): Promise<void> {
  await db.schema.createType('pet_types_enum').asEnum(['Cat', 'Dog']).execute()
  await db.schema
    .createTable('pets')
    ...
    .addColumn('type', sql`pet_types_enum`, col => col.notNull())
    ...
    .execute()
}

Additionally, you will need to leverage the STI decorator on your child models, like so:

class Pet extends ApplicationModel {
  ...
  public type: DreamColumn<Pet, 'type'>
  ...
}

@STI(Pet)
class Cat extends Pet {}

@STI(Pet)
class Dog extends Pet {}

Whenever an STI model is persisted to the database, the type field will automaticlly be populated with the class name of the STI model:

const cat = await Cat.create()
cat.type
// 'Cat'

const dog = await Dog.create()
dog.type
// 'Dog'

Additionally, whenever running queries against an STI model, the type field will automatically by added to your query:

await Pet.all()
// [Cat{}, Dog{}, ...]

await Cat.all()
// [Cat{}, Cat{}, ...]

await Dog.all()
// [Dog{}, Dog{}, ...]

The sti-child generator makes it easy to create STI children:

yarn psy g:sti-child Foo/Bar extends Foo/Base hello:string