How to transform a JSON array nested inside an object inside another array in Postgres? - arrays

Question

I'm using Postgres 9.6 and have a JSON field called credits with the following structure; A list of credits, each with a position and multiple people that can be in that position.
[
{
"position": "Set Designers",
people: [
"Joe Blow",
"Tom Thumb"
]
}
]
I need to transform the nested people array, which are currently just strings representing their names, into objects that have a name and image_url field, like this
[
{
"position": "Set Designers",
people: [
{ "name": "Joe Blow", "image_url": "" },
{ "name": "Tom Thumb", "image_url": "" }
]
}
]
So far I've only been able to find decent examples of doing this on either the parent JSON array or on an array field nested inside a single JSON object.
So far this is all I've been able to manage and even it is mangling the result.
UPDATE campaigns
SET credits = (
SELECT jsonb_build_array(el)
FROM jsonb_array_elements(credits::jsonb) AS el
)::jsonb
;

Answer 1

Create an auxiliary function to simplify the rather complex operation:
create or replace function transform_my_array(arr jsonb)
returns jsonb language sql as $$
select case when coalesce(arr, '[]') = '[]' then '[]'
else jsonb_agg(jsonb_build_object('name', value, 'image_url', '')) end
from jsonb_array_elements(arr)
$$;
With the function the update is not so horrible:
update campaigns
set credits = (
select jsonb_agg(jsonb_set(el, '{people}', transform_my_array(el->'people')))
from jsonb_array_elements(credits::jsonb) as el
)::jsonb
;
Working example in rextester.