How to improve this query using array or json constructor? - postgresql

Question

how are you?
I am wondering how to improve this query to return something better to work with. Let me show the tables, the current query and my idea first:
Tables
users
nfts
here owner_id is a fk to users.id
users_nfts (here I save all the creators of the nft, one nft could have more than one creator. This is to calculate royalties later)
Current query and explanation
To be able to code a "buy" nft process (in nodejs) I want to retrieve some data about the nft to buy:
Its price
Its current owner
The creators (to calculate the royalties and update their balances)
SELECT nfts.id, price, owner_id, owner.balance as owner_balance, creators.user_id, users.balance
FROM nfts
INNER JOIN users_nfts as creators
ON nfts.id = creators.nft_id
INNER JOIN users
ON creators.user_id = users.id
INNER JOIN users as owner
ON nfts.owner_id = owner.id
WHERE nfts.id = ${nft_id}
The query works but it's horrible because it retrieves me repeated data (this is what I want to solve). The red square means the repeated data.
What I would like to achieve
I would like to make a query so all the data about the NFT comes in one row. To do that, I need to retrieve the user_id and balance inside an array of tuples or in a json.
The result in my backend could be something like (any ideas here are welcome):
{
"id": "ea850c65-818e-40bd-bb06-af69eaeda4a6", // nft id
"price": 42,
"owner_id": "1134e9e0-02ae-4567-9adf-220ead36a6ef",
"owner_balance": 100,
"creators": [
{
"user_id": "1134e9e0-02ae-4567-9adf-220ead36a6ef",
"balance": 100,
},
{
"user_id": "2134e9e0-02ae-4567-9adf-220ead36a6ea",
"balance": 35,
},
],
},
Thanks in advance for any tips :)

Answer 1

I achieved what I want with this query, using json_agg and json_build_object
SELECT nfts.id, price, owner_id, owner.balance as owner_balance, json_agg(json_build_object('user_id', creators.user_id, 'balance', users.balance)) as creators
FROM nfts
INNER JOIN users_nfts as creators
ON nfts.id = creators.nft_id
INNER JOIN users
ON creators.user_id = users.id
INNER JOIN users as owner
ON nfts.owner_id = owner.id
WHERE nfts.id = ${nft_id}
GROUP BY nfts.id, owner.id;
The query produces the following output:
{
"rows": [
{
"id": "d87716ec-4005-4ccb-9970-6769adec3aa1",
"price": 42,
"owner_id": "7dd619dd-b997-4351-9541-4d8989c58667",
"owner_balance": 58,
"creators": [
{
"user_id": "1134e9e0-02ae-4567-9adf-220ead36a6ef",
"balance": 137.8
},
{
"user_id": "492851bb-dead-4c9d-b9f6-271dcf07a8bb",
"balance": 104.2
}
]
}
]
}
Hope someone else can find this useful.