Allow passing in db interfaces for insert operations

Currently Kysely relies on the user passing in db.generated when inserting not null columns with default values since it only knows these columns are not null. If we could pass in separate interfaces for insert operations this process would be more type-safe.

Here’s an idea for the api

interface Person {
  id: number
  first_name: string
  last_name: string
  gender: 'male' | 'female' | 'other'
}

interface Database {
  person: Person
}

interface InsertablePerson {
  // id is generated as identity
  id?: number
  first_name: string
  last_name: string
  gender: 'male' | 'female' | 'other'
}

interface InsertableDatabase {
  person: InsertablePerson
}

// Insertable interfaces are passed to the second type param.
const db = new Kysely<Database, InsertableDatabase>({
  dialect: new PostgresDialect({
    host: 'localhost',
    database: 'kysely_test',
  })
})

Some libraries that generate db table interfaces, for example kanel, also generate interfaces for insert operations, which accounts for generated values. It’d be very much useful if we could pass those interfaces to Kysely.

[koskimas]

Reopened this as I’m working on a POC for this after multiple requests.

[koskimas]

There’s some discussion about this idea here