Support json_agg(column_ref).

[igalklebanov]

Hey 👋

Currently eb.fn.jsonAgg supports table names and expressions as inputs. In such cases, the return type is a JSON object array.

json_agg also supports passing a column reference. In such cases, the return type is a literal array.
We should support this.

const result = await db
  .selectFrom('person')
  .innerJoin('pet', 'pet.owner_id', 'person.id')
  .select((eb) =>
    eb.fn.jsonAgg('pet.name').as('person_pets')
  )
  .executeTakeFirstOrThrow()

The return type would be { person_pets: string[] }.

[koskimas]

Good idea! jsonAgg is also quite broken with left joins, and there's nothing we can do about it easily. Not related to this issue though.

We express left joined tables in the DB generic as tables where each column is nullable. While this works in most cases, in case of jsonAgg it produces objects with nullable properties when it should produce nullable objects with normal property types 😬

We have no way to tell if a column is nullable in DB because it's actually nullable or if it was put there using a left join.

We could express left joined tables in DB like this

{
  person: Person,
  leftJoined: Pet | null
}

But that's a big type overhaul and most likely a breaking change.