Add and remove elements unique to a Postgres jsonb sub key: Short a Set implemetation
UPDATE public.mytable SET
jsonfieldname = jsonb_set( jsonfieldname, '{json_obj_key}', array_to_json(
array_remove( ARRAY(
SELECT json_array_elements_text( COALESCE( jsonfieldname::json->'json_obj_key', '[]' ) )
), 'Element to remove' )
)::jsonb )
WHERE id = 23
RETURNING *;
UPDATE public.mytable SET
jsonfieldname = jsonb_set( jsonfieldname, '{json_obj_key}', array_to_json(
ARRAY(
SELECT DISTINCT( UNNEST( ARRAY(
SELECT json_array_elements_text( COALESCE( jsonfieldname::json->'json_obj_key', '[]' ) )
) || ARRAY['Element to add'] ) )
)
)::jsonb )
WHERE id = 23
RETURNING *;