Create parent-children query from many-to-many relationship - sql

Question

Good day,
I struggle to create a query in Postgres to obtain a many-to-many relationship in parent-children form.
There are two tables:
'Projects'
projects table
'Services'
services table
They are connected with the third project_service table
project_service
The query SELECT projects.id_project, projects.title, projects.level, services.id_service, services.service FROM projects, services, project_service WHERE projects.id_project = project_service.id_project AND services.id_service = project_service.id_service return this table:
query result table
How to write a query to get this table in parent-children form like this:
[
{ "id": "1000", "level": "Projects", "title": "Project 1", "children": [
{ "id": "2000", "service": "Service 1},
{ "id": "2001", "service": "Service 2},
{ "id": "2002", "service": "Service 3},
{ "id": "2003", "service": "Service 4}
]},
{ "id": "1001", "level": "Projects", "title": "Project 2", "children": [
{ "id": "2004", "service": "Service 5}
]}]
Thank you for help

Answer 1

Is this what you mean?
with svc_json as (
select id_service, to_jsonb(services) as svc
from services
), together as (
select p.*, jsonb_agg(s.svc) as children
from project_service ps
join svc_json s on s.id_service = ps.id_service
join projects p on p.id_project = ps.id_project
group by p.id_project, p.title, p.level
)
select jsonb_pretty(jsonb_agg(to_jsonb(together)))
from together;
jsonb_pretty
-----------------------------------------
[ +
{ +
"level": "Projects", +
"title": "Project 1", +
"children": [ +
{ +
"service": "Service 1",+
"id_service": 2000 +
}, +
{ +
"service": "Service 2",+
"id_service": 2001 +
}, +
{ +
"service": "Service 3",+
"id_service": 2002 +
}, +
{ +
"service": "Service 4",+
"id_service": 2003 +
} +
], +
"id_project": 1000 +
}, +
{ +
"level": "Projects", +
"title": "Project 2", +
"children": [ +
{ +
"service": "Service 5",+
"id_service": 2004 +
} +
], +
"id_project": 1001 +
} +
]
(1 row)