Postgres add additional field to json payload index within an array prior to inserting as record set into database - postgresql

Question

I'm creating a stored procedure in postgres which takes a json and inserts into a table by performing a json_to_recordset command.
Prior to inserting the record set into a SQL table with that command I want to add an additional field as a index to the json in the json array.
Is this possible?
For each index in the array I want to add "current_status": "pending"
[
{
"batch_id": "40",
"state_id": "10"
},
{
"batch_id": "40",
"state_id": "10"
}
]
after
[
{
"batch_id": "40",
"state_id": "10",
"current_status": "pending"
},
{
"batch_id": "40",
"state_id": "10"
"current_status": "pending"
}
]
Another option is updating the only NEW records in the table after the fact.
I'm new to postgres and have been reading through the documentation.

Answer 1

Based on your added comment, the current_status = 'pending' should be added as part of the insert into your target table instead of appending the key to the json objects.
insert into target_table (batch_id, state_id, current_status)
select batch_id, state_id, 'pending' as current_status
from json_to_recordset(<json>) as x(batch_id text, state_id text);

Answer 2

Adding to Mike's correct answer, in the case we want to modify existing tables with json arrays to include the status we may:
-- First create the table
CREATE TABLE myJson AS
SELECT '[
{
"batch_id": "40",
"state_id": "10"
},
{
"batch_id": "50",
"state_id": "60"
}
]'::json js;
WITH unnest_and_concat AS (
SELECT json_array_elements(js)::jsonb || json_build_object('current_status', 'pending')::jsonb jee
FROM myJson)
SELECT json_agg(jee)::json
FROM unnest_and_concat;
Of course this is only intended to work for a table with these rows (for illustration). If the objective is to update the entire table then we can do that (ideally with a LATERAL JOIN) mixed with an update statement. Looks like:
UPDATE myJson
SET old_col=new_col
FROM <insert subquery or table>
WHERE myJson.id = new_table.id;
Nevertheless, I would recommend modifying upon insert rather than updating.