More aggregate functions such as `array_agg` and `json_agg`

It seems like this library currently only supports a subset of aggregate functions like count, max and min. Would it be possible to support array_agg or json_agg?

[rliang]

Thanks for the help. My use case is mostly within subqueries. After fiddling around, I came up with the following generic wrapper, which seems to produce both correct SQL and Typescript types:

function json_agg<DB, TB extends keyof DB, O = {}>(qb: QueryBuilder<DB, TB, O>) {
  return db.raw<O[]>(`coalesce((select jsonb_agg(x) from (??) x), '[]'::jsonb)`, [qb]);
}

await db
    .selectFrom("person")
    .select([
      "id",
      (qb) =>
        json_agg(
          qb
            .subQuery("pet")
            .whereRef("pet.owner_id", "=", "person.id")
            .select("pet.name")
        ).as("pets"),
    ])
    .executeTakeFirst() // type is { id: string, pets: { name: string }[] }

[koskimas]

I don’t know. Maybe. That’s the thing. It’s really difficult to write helpers that work in all cases, but pretty easy to write helpers that work for your own use case. For example, you could write this type-safe helper:

function json_agg<T extends keyof Database>(table: T): RawBuilder<Array<Database[T]>> {
  return db.raw(`json_agg(${table})`)
}

where Database is from Kysely<Database>.

await db
  .selectFrom('person')
  .innerJoin('pet', 'pet.owner_id', 'person.id')
  .select(json_agg('pet').as('pets'))