Postgresql join on array and transform to json - sql

Question

I would like to make a join on array containing ids and transform the result of this subselect into json (json array).
I have the following model:

The lnam_refs column contains identifiers that are related to the lnam column
I would like transform the column lnam_refs into something like [row_to_json(), row_to_json()] or [] or [row_to_json()] or …
I tried several methods but I can not achieve a clean result…
To try to be clearer :
Table in input:
id | label | lnam | lnam_refs
--------+----------------------+----------+-----------------------
1 | 'master1' | 11111111 | {33333333}
2 | 'master2' | 22222222 | {44444444,55555555}
3 | 'slave1' | 33333333 | {}
4 | 'slave2' | 44444444 | {}
5 | 'slave3' | 55555555 | {}
6 | 'master3' | 66666666 | {}
Results Expected:
id | label | lnam | lnam_refs | slaves
--------+----------------------+----------+-----------------------+---------------------------------
1 | 'master1' | 11111111 | {33333333} | [ {id: 3, label: 'slave1', lnam: 33333333, lnam_refs: []} ]
2 | 'master2' | 22222222 | {44444444,55555555} | [ {id: 4, label: 'slave2', lnam: 44444444, lnam_refs: []}, {id: 5, label: 'slave3', lnam: 55555555, lnam_refs: []} ]
6 | 'master3' | 66666666 | {} | []
Thanks for your help !

Answer 1

Here's one way to do it. (I created a table called t with that data you supplied.)
SELECT *, (SELECT JSON_AGG(ROW_TO_JSON(t2)) FROM t t2 WHERE label LIKE 'slave%' AND lnam = ANY(t1.lnam_refs)) AS slaves
FROM t t1
WHERE label LIKE 'master%'
I use the label field in the WHERE clause as I don't know how else you're determining which records should be master etc.
Result:
1;master1;11111111;{33333333};[{"id":3,"label":"slave1","lnam":33333333,"lnam_refs":[]}]
2;master2;22222222;{44444444,55555555};[{"id":4,"label":"slave2","lnam":44444444,"lnam_refs":[]}, {"id":5,"label":"slave3","lnam":55555555,"lnam_refs":[]}]
6;master3;66666666;{};