How to return data in JSON hierarchy? - postgresql

Question

For the following data tables and function in pg12
create table orders
(
orderid integer, grandtotal numeric(10, 2)
)
create table odetails
(
orderid integer, detailid integer, description text
)
create function jorder() returns json as
begin
return query select od.orderid, od.grandtotal, ds.detailid, ds.description
from orders od
join odetails ds on od.orderid = ds.orderid;
end;
How do I get return data in a JSON hierarchy like below?
[{
"orderid": 1,
"grandtotal": 100.00,
"details": [{
"detailid": 11,
"description": "pen"
},
{
"detailid": 12,
"description": "orange"
}
]
}, {
"orderid": 2,
"grandtotal": 200.00,
"details": [{
"detailid": 21,
"description": "book"
},
{
"detailid": 22,
"description": "coffee"
},
{
"detailid": 23,
"description": "tea"
}
]
}]

Answer 1

You should look into json functions . You need json_build_object to form the objects and json_agg to aggregate them into json array:
CREATE FUNCTION jorder()
RETURNS json
LANGUAGE sql
AS $$
SELECT
json_agg(orders.order)
FROM (
SELECT
json_build_object(
'orderid', od.orderid,
'grandtotal', od.grandtotal,
'details', array_agg(
json_build_object(
'detailid', ds.detailid,
'description', ds.description
)
)
) as order
FROM
orders od
JOIN odetails ds on od.orderid = ds.orderid
GROUP BY
od.orderid, od.grandtotal
) as orders
$$;
Example at db<>fiddle