How to get JSON object from PostgreSQL?

Question

PostgreSQL

PostgreSQL 9.4
How to get data like this:

parentTableFirstProp: 'string',
parentToChildReference: [
    {childTableFirstProp: 'another string'},
    {childTableFirstProp: 'yet another string'}
}]

instead of this:

[{
    parentTableFirstProp: 'string',
    childTableFirstProp: 'another string',
},{
    parentTableFirstProp: 'string',
    childTableFirstProp: 'yet another string'
}]

Is it possible to do this with some simple query, or do you need to do 2+ SELECTs each time and then nest one response into another using aliases?
Thank you for your time!

Answer 1

select row_to_json(t)
from (
select "ParentTable"."parentTableFirstProp", (
select array_to_json(array_agg(row_to_json(child)))
  from (
    select "childTableFirstProp"
    from "ChildTable"
    where "ChildTable"."id"="ParentTable"."parentToChildReference"
  ) child

  ) as parentToChildReference
from "ParentTable"
) t

Answer 2

Something like this:

select row_to_json(j.*) from (

  select  'string' as parentTableFirstProp, to_json(

    (
    select to_json(array_agg(r.*)) from (
      select s as childTableFirstProp from (select unnest('{another string,yet another string}'::text[]) as s) _
    )as r
    )
  ) as parentToChildReference

) as j

Answer 3

above is not according to the json standard, so postgres returns everything correctly to you. redo it so that everything is perceived according to the standard