PG: Aggregate parent/Child records into JSON object

gistfile1.sql

select artists.id as artist_id, (select row_to_json(artist_albums) 
from 
(
  select a.name,
  (
    select array_to_json(array_agg(albums)) 
    from albums where artist_id = a.id
  ) as albums
    from artists as a where a.id = artists.id
) as artist_albums) as artist from artists where artists.id = 12