Prisma - How to group children together in self-relation query - database

Question

I'm having a following model in my schema:
model Collection {
id String #id #default(cuid())
title String
createdAt DateTime #default(now())
updatedAt DateTime #updatedAt
parent Collection? #relation("CollectionChildren", fields: [parentId], references: [id])
parentId String?
children Collection[] #relation("CollectionChildren")
}
What I have is a self-relation of collections. They can have unlimited levels.
Now, I want to query and order and list them so that the final result looks like this:
Collection 1
Collection 2
Collection 2 Child 1
Collection 2 Child 2
Collection 2 Child 3
Collection 3
Collection 3 Child 1
Collection 3 Child 1 Sub-child 1
Collection 3 Child 2
Collection 3 Child 3
Collection 4
The problem is that I have no idea how to query then so that they are ordered by title, while also grouped by parent.
Is that even possible in Prisma/Postgres?

Answer 1

It would be difficult to get all the children without knowing the depth of the levels of children (as you mentioned that there could be unlimited levels).
Prisma has a feature request to Support recursive relationships #3725
As a workaround, you would need to use Raw Query.
The SQL query could look something like this:
WITH RECURSIVE collection_tree AS (
SELECT id, title, parentId
FROM Collection
WHERE parentId IS NULL
UNION ALL
SELECT c.id, c.title, c.parentId
FROM Collection c
JOIN collection_tree ct ON ct.id = c.parentId
)
SELECT *
FROM collection_tree
ORDER BY title;
This query uses a recursive CTE to first select the top-level collections (where the parentId is null), and then select all the children of those collections by joining the collection_tree CTE with the Collection table on the parentId. The result is a flattened list of all the collections and their children, ordered by the title field.