JSON object: Query a value from unkown node based on a condition - json

Question

I'm trying to query two values (DISCOUNT_TOTAL and ITEM_TOTAL) from a JSON object in a PostgreSQL database. Take the following query as reference:
SELECT
mt.customer_order
totals -> 0 -> 'amount' -> centAmount DISCOUNT_TOTAL
totals -> 1 -> 'amount' -> centAmount ITEM_TOTAL
FROM
my_table mt
to_jsonb(my_table.my_json -> 'data' -> 'order' -> 'totals') totals
WHERE
mt.customer_order in ('1000001', '1000002')
The query code works just fine, the big problem is that, for some reason out of my control, the values DISCOUNT_TOTAL and ITEM_TOTAL some times change their positions in the JSON object from one customer_order to other:
JSON Object
So i cannot aim to totals -> 0 -> 'amount' -> centAmount assuming that it contains the value related to type : DISCOUNT_TOTAL (same for type: ITEM_TOTAL). Is there any work around to get the correct centAmount for each type?

Answer 1

Use a path query instead of hardcoding the array positions:
with sample (jdata) as (
values (
'{
"data": {
"order": {
"email": "something",
"totals": [
{
"type": "ITEM_TOTAL",
"amount": {
"centAmount": 14990
}
},
{
"type": "DISCOUNT_TOTAL",
"amount": {
"centAmount": 6660
}
}
]
}
}
}'::jsonb)
)
select jsonb_path_query_first(
jdata,
'$.data.order.totals[*] ? (#.type == "DISCOUNT_TOTAL").amount.centAmount'
) as discount_total,
jsonb_path_query_first(
jdata,
'$.data.order.totals[*] ? (#.type == "ITEM_TOTAL").amount.centAmount'
) as item_total
from sample;
db<>fiddle here
EDIT: In case your PostgreSQL version does not support json path queries, you can do it by expanding the array into rows and then doing a pivot by case and sum:
with sample (order_id, jdata) as (
values ( 1,
'{
"data": {
"order": {
"email": "something",
"totals": [
{
"type": "ITEM_TOTAL",
"amount": {
"centAmount": 14990
}
},
{
"type": "DISCOUNT_TOTAL",
"amount": {
"centAmount": 6660
}
}
]
}
}
}'::jsonb)
)
select order_id,
sum(
case
when el->>'type' = 'DISCOUNT_TOTAL' then (el->'amount'->'centAmount')::int
else 0
end
) as discount_total,
sum(
case
when el->>'type' = 'ITEM_TOTAL' then (el->'amount'->'centAmount')::int
else 0
end
) as item_total
from sample
cross join lateral jsonb_array_elements(jdata->'data'->'order'->'totals') as a(el)
group by order_id;
db<>fiddle here