How to update JSON array with PostgreSQL - arrays

Question

I have the following inconvenience, I want to update a key of an JSON array using only PostgreSQL. I have the following json:
[
{
"ch":"1",
"id":"12",
"area":"0",
"level":"Superficial",
"width":"",
"length":"",
"othern":"5",
"percent":"100",
"location":" 2nd finger base"
},
{
"ch":"1",
"id":"13",
"area":"0",
"level":"Skin",
"width":"",
"length":"",
"othern":"1",
"percent":"100",
"location":" Abdomen "
}
]
I need to update the "othern" to another number if the "othern" = X
(X is any number that I pass to the query. Example, update othern if othern = 5).
This JSON can be much bigger, so I need something that can iterate in the JSON array and find all the "othern" that match X number and replace with the new one. Thank you!
I have tried with these functions json of Postgresql, but I do not give with the correct result:
SELECT * FROM jsonb_to_recordset('[{"ch":"1", "id":"12", "area":"0", "level":"Superficial", "width":"", "length":"", "othern":"5", "percent":"100", "location":" 2nd finger base"}, {"ch":"1", "id":"13", "area":"0", "level":"Skin", "width":"", "length":"", "othern":"1", "percent":"100", "location":" Abdomen "}]'::jsonb)
AS t (othern text);
I found this function in SQL that is similar to what I need but honestly SQL is not my strength:
CREATE OR REPLACE FUNCTION "json_array_update_index"(
"json" json,
"index_to_update" INTEGER,
"value_to_update" anyelement
)
RETURNS json
LANGUAGE sql
IMMUTABLE
STRICT
AS $function$
SELECT concat('[', string_agg("element"::text, ','), ']')::json
FROM (SELECT CASE row_number() OVER () - 1
WHEN "index_to_update" THEN to_json("value_to_update")
ELSE "element"
END "element"
FROM json_array_elements("json") AS "element") AS "elements"
$function$;
UPDATE plan_base
SET atts = json_array_update_index([{"ch":"1", "id":"12", "area":"0", "level":"Superficial", "width":"", "length":"", "othern":"5", "percent":"100", "location":" 2nd finger base"}, {"ch":"1", "id":"13", "area":"0", "level":"Skin", "width":"", "length":"", "othern":"1", "percent":"100", "location":" Abdomen "}], '{"othern"}', '{"othern":"71"}'::json)
WHERE id = 2;

Answer 1

The function you provided changes a JSON input, gives out the changed JSON and updates a table parallel.
For a simple update, you don't need a function:
demo:db<>fiddle
UPDATE mytable
SET myjson = s.json_array
FROM (
SELECT
jsonb_agg(
CASE WHEN elems ->> 'othern' = '5' THEN
jsonb_set(elems, '{othern}', '"7"')
ELSE elems END
) as json_array
FROM
mytable,
jsonb_array_elements(myjson) elems
) s
jsonb_array_elements() expands the array into one row per element
jsonb_set() changes the value of each othern field. The relevant JSON objects can be found with a CASE clause
jsonb_agg() reaggregates the elements into an array again.
This array can be used to update your column.
If you really need a function which gets the parameters and returns the changed JSON, then this could be a solution. Of course, this doesn't execute an update. I am not quite sure if you want to achieve this:
demo:db<>fiddle
CREATE OR REPLACE FUNCTION json_array_update_index(_myjson jsonb, _val_to_change int, _dest_val int)
RETURNS jsonb
AS $$
DECLARE
_json_output jsonb;
BEGIN
SELECT
jsonb_agg(
CASE WHEN elems ->> 'othern' = _val_to_change::text THEN
jsonb_set(elems, '{othern}', _dest_val::text::jsonb)
ELSE elems END
) as json_array
FROM
jsonb_array_elements(_myjson) elems
INTO _json_output;
RETURN _json_output;
END;
$$ LANGUAGE 'plpgsql';
If you want to combine both as you did in your question, of course, you can do this:
demo:db<>fiddle
CREATE OR REPLACE FUNCTION json_array_update_index(_myjson jsonb, _val_to_change int, _dest_val int)
RETURNS jsonb
AS $$
DECLARE
_json_output jsonb;
BEGIN
UPDATE mytable
SET myjson = s.json_array
FROM (
SELECT
jsonb_agg(
CASE WHEN elems ->> 'othern' = '5' THEN
jsonb_set(elems, '{othern}', '"7"')
ELSE elems END
) as json_array
FROM
mytable,
jsonb_array_elements(myjson) elems
) s
RETURNING myjson INTO _json_output;
RETURN _json_output;
END;
$$ LANGUAGE 'plpgsql';