如何为 json_build_object 添加默认值 postgresql

Question

My json looks like this:-

{"DestinationLists": [{"name": "TVNZ, Mediaworks, Choice", "destinations": []}, { "name": "TVNZ, Discovery", "destinations": [165, 183, 4155]}]}

My desired output is one row for each object in the array like:-

{"name" : "TVNZ, Mediaworks, Choice", "destinations" : []}
{"name" : "TVNZ, Discovery", "destinations" : [{"Id" : 165}, {"Id" : 183}, {"Id" : 4155}]}

My query is this:-

WITH ExpandedData AS (
    SELECT
        "Id",
        setting,
        json_build_object(
            'name',
             dl->>'name',
             'destinations',
             json_agg(
               json_build_object('Id',dld::text::int)
             )
        ) as DestinationListItem
    FROM
        feature.settings, 
        jsonb_array_elements(value->'DestinationLists') dl,
        jsonb_array_elements(dl->'destinations') dld
    GROUP BY
        "Id",dl->>'name'
)
select * from ExpandedData

But this query is missing destinations where the array is empty so the result I am getting from the query is:-

{"name" : "TVNZ, Discovery", "destinations" : [{"Id" : 165}, {"Id" : 183}, {"Id" : 4155}]}

just one row instead of two. How do I update this query to get the desired outcome?

DBFiddle here:- https://www.db-fiddle.com/f/tDA7SajDoWhXrQaAa1j2qN/0

EDIT: I have been able to further drill down my problem, so the issue is basically happening from this line of the query:-

jsonb_array_elements(dl->'destinations') dld

Basically when the destinations array is empty then jsonb_array_elements does not return anything so I guess the right solution here would be to somehow return an empty array from jsonb_array_elements when an empty array is passed to it.

Answer 1

You can use a recursive cte :

with recursive cte(js, ind, r) as (
   select js, 1, case when json_array_length(js -> 'DestinationLists' -> 0 -> 'destinations') = 0 then (js -> 'DestinationLists' -> 0)::jsonb else jsonb_set(js::jsonb, concat('{DestinationLists,', 0, ',destinations}')::text[], (select array_to_json(array_agg(json_build_object('Id', value))) from json_array_elements(js -> 'DestinationLists' -> 0 -> 'destinations'))::jsonb) end from data
   union all
   select js, ind+1, case when json_array_length(js -> 'DestinationLists' -> ind -> 'destinations') = 0 then (js -> 'DestinationLists' -> ind)::jsonb else (jsonb_set(js::jsonb, concat('{DestinationLists,', ind, ',destinations}')::text[], (select array_to_json(array_agg(json_build_object('Id', value))) from json_array_elements(js -> 'DestinationLists' -> ind -> 'destinations'))::jsonb) -> 'DestinationLists' -> ind)::jsonb end from cte where ind < json_array_length(js -> 'DestinationLists')
)
select r from cte;

Output:

r
{"name": "TVNZ, Mediaworks, Choice", "destinations": []}
{"name": "TVNZ, Discovery", "destinations": [{"Id": 165}, {"Id": 183}, {"Id": 4155}]}