Sorting results in recursive query - sql

Question

I have a basic CATEGORIES-like table consisting of fields like the primary_key, a parent_id, title and a sorting integer.
I am able to retrieve the results using CTE and convert them to a json array but I want to fetch them, aside from the parent_id, based on the sorting value.
So far:
with recursive parents as
(
select n.boat_type_id, n.title, '{}'::int[] as parents, 0 as level
from boat_types n
where n.parent_id is NULL
union all
select n.boat_type_id, n.title, parents || n.parent_id, level+1
from parents p
join boat_types n on n.parent_id = p.boat_type_id
where not n.boat_type_id = any(parents)
),
children as
(
select n.parent_id, json_agg(jsonb_build_object('title', n.title->>'en'))::jsonb as js
from parents tree
join boat_types n using(boat_type_id)
where level > 0 and not boat_type_id = any(parents)
group by n.parent_id
union all
select n.parent_id, jsonb_build_object('category', n.title->>'en') || jsonb_build_object('subcategories', js) as js
from children tree
join boat_types n on n.boat_type_id = tree.parent_id
)
select jsonb_agg(js) as categories
from children
where parent_id is null
The above provides me with the result-set and the structure I want, but how can I make them follow the sorting value for both the nodes and the leafs.
Sample response:
[
{
"sorting":0,
"category":"Motor",
"subcategories":[
{
"title":"Motor Yacht",
"sorting":2
},
{
"title":"Mega Yacht",
"sorting":1
}
]
},
{
"sorting":1,
"category":"Sailing",
"subcategories":[
{
"title":"Sailing Yacht",
"sorting":2
},
{
"title":"Cruiser Racer",
"sorting":1
}
]
},
{
"sorting":2,
"category":"Catamaran",
"subcategories":[
{
"title":"Catamaran",
"sorting":2
},
{
"title":"Trimaran",
"sorting":1
}
]
},
{
"sorting":3,
"category":"Other",
"subcategories":[
{
"title":"Other",
"sorting":2
},
{
"title":"Airboat",
"sorting":1
}
]
}
]
I have tried aggregating the sorting values in ARRAY fields and sort by it, but it doesn't work.

Answer 1

You can use the order by clause in the json_agg() aggregate:
...
children as
(
select
n.parent_id,
json_agg(jsonb_build_object('title', n.title->>'en', 'sorting', n.sorting) order by n.sorting)::jsonb as js
from parents tree
join boat_types n using(boat_type_id)
where level > 0 and not boat_type_id = any(parents)
group by n.parent_id
union all
select
n.parent_id,
jsonb_build_object('category', n.title->>'en', 'sorting', n.sorting) || jsonb_build_object('subcategories', js) as js
from children tree
join boat_types n on n.boat_type_id = tree.parent_id
)
...