JSONB Data Type Modification in Postgresql - postgresql

Question

I have a doubt with modification of jsonb data type in postgres
Basic setup:-
array=> ["1", "2", "3"]
and now I have a postgresql database with an id column and a jsonb datatype column named lets just say cards.
id cards
-----+---------
1 {"1": 3, "4": 2}
thats the data in the table named test
Question:
How do I convert the cards of id->1 FROM {"1": 3, "4": 2} TO {"1": 4, "4":2, "2": 1, "3": 1}
How I expect the changes to occur:
From the array, increment by 1 all elements present inside the array that exist in the cards jsonb as a key thus changing {"1": 3} to {"1": 4} and insert the values that don't exist as a key in the cards jsonb with a value of 1 thus changing {"1":4, "4":2} to {"1":4, "4":2, "2":1, "3":1}
purely through postgres.
Partial Solution
I asked a senior for support regarding my question and I was told this:-
Roughly (names may differ): object keys to explode cards, array_elements to explode the array, left join them, do the calculation, re-aggregate the object. There may be a more direct way to do this but the above brute-force approach will work.
So I tried to follow through it using these two functions json_each_text(), json_array_elements_text() but ended up stuck halfway into this as well as I was unable to understand what they meant by left joining two columns:-
SELECT jsonb_each_text(tester_cards) AS each_text, jsonb_array_elements_text('[["1", 1], ["2", 1], ["3", 1]]') AS array_elements FROM tester WHERE id=1;
TLDR;
Update statement that checks whether a range of keys from an array exist or not in the jsonb data and automatically increments by 1 or inserts respectively the keys into the jsonb with a value of 1
Now it might look like I'm asking to be spoonfed but I really haven't managed to find anyway to solve it so any assistance would be highly appreciated 🙇

Answer 1

The key insight is that with jsonb_each and jsonb_object_agg you can round-trip a JSON object in a subquery:
SELECT id, (
SELECT jsonb_object_agg(key, value)
FROM jsonb_each(cards)
) AS result
FROM test;
(online demo)
Now you can JOIN these key-value pairs against the jsonb_array_elements of your array input. Your colleague was close, but not quite right: it requires a full outer join, not just a left (or right) join to get all the desired object keys for your output, unless one of your inputs is a subset of the other.
SELECT id, (
SELECT jsonb_object_agg(COALESCE(obj_key, arr_value), …)
FROM jsonb_array_elements_text('["1", "2", "3"]') AS arr(arr_value)
FULL OUTER JOIN jsonb_each(cards) AS obj(obj_key, obj_value) ON obj_key = arr_value
) AS result
FROM test;
(online demo)
Now what's left is only the actual calculation and the conversion to an UPDATE statement:
UPDATE test
SET cards = (
SELECT jsonb_object_agg(
COALESCE(key, arr_value),
COALESCE(obj_value::int, 0) + (arr_value IS NOT NULL)::int
)
FROM jsonb_array_elements_text('["1", "2", "3"]') AS arr(arr_value)
FULL OUTER JOIN jsonb_each_text(cards) AS obj(key, obj_value) ON key = arr_value
);
(online demo)