Add JSON_OBJECT to one of multiple arrays - mysql

Question

I have several tables whose records have a type identifier. For example a table AUTOS has a MANUFACTURER field. I'd like to be able to create an json_object for each row and add that object to a manufacturer specific array, e.g.
{
fordCars: [],
chevyCars: []
}
The arrays are members of a parent object (let's name it #parent)
As I indicated I have several such tables that should be treated the same way.
I thought I might define a variable
DECLARE #mfgs json;
initialize it as follows:
SET #mfgs = '{
"fordCars": [],
"chevyCars": []
}';
I thought I could populate the arrays as follows but the arrays in #mfg are empty:
SELECT CASE
WHEN MANUFACTURER='FORD' THEN SELECT JSON_ARRAY_APPEND(#mfgs, '$.fordCars', JSON_OBJECT(
'MANUFACTURER',d.MANUFACTURER,
'MAKE',d.MAKE,
'MODEL',d.MODEL
))
WHEN MANUFACTURER='CHEVY' THEN SELECT JSON_ARRAY_APPEND(#mfgs, '$.chevyCars', JSON_OBJECT(
'MANUFACTURER',d.MANUFACTURER,
'MAKE',d.MAKE,
'MODEL',d.MODEL
))
END
from AUTOS d
I would then:
JSON_MERGE_PRESERVE(#parent, #mfgs)
The above does not work and in any case requires that I repeat all json/sql mappings for each case statement.
Does anyone know how I can accumulate json_objects in one of multiple arrays based on the value, in this case of MANUFACTURER?
Installation is mySQL 8.023.
Thanks in advance.

Answer 1

An answer that eliminates the issue of having to repeat each of the AUTOS table fields for each grouping of MANUFACTURER. I am still unable however to use JSON_* functions to provide arguments to JSON_MERGE_PRESERVE.
IF someone knows how to accomplish this it would make for a more elegant solution imho.
SET json_auto_detail = (select JSON_MERGE_PRESERVE(json_auto_detail,
(select concat('{', GROUP_CONCAT(jsonString SEPARATOR "," ),'}') from (
SELECT concat('"', mfgArrayName, '":', mfgArrayObj) as 'jsonString' from (
(select
if (MANUFACTURER='FORD', 'fordCars',
if (MANUFACTURER='Chevy', 'chevyCars')) as 'mfgArrayName',
json_arrayagg(JSON_OBJECT(
'make', MANUFACTURER,
'model', MODEL,
'id', ID
)) as 'mfgArrayObj'
from AUTOS
where MANUFACTURER in ('FORD', 'CHEVY')
group by MANUFACTURER
)
) as autos -- up to 2 rows of auto json objects
) as mAutos))
); -- autos merged with json_auto_detail