How to create hierarchal json object using ltree query results? (postgresql)

Question

I'm trying to create a storage system for custom categories using postgres.

After looking around for potential solutions I settled on trying to use ltree ;

Here is an example of raw data below;

+----+---------+---------------------------------+-----------+
| id | user_id |              path               |   name    |
+----+---------+---------------------------------+-----------+
|  1 |       1 | root.test                       | test      |
|  2 |       1 | root.test.inbox                 | inbox     |
|  3 |       1 | root.personal                   | personal  |
|  4 |       1 | root.project                    | project   |
|  5 |       1 | root.project.idea               | idea      |
|  6 |       1 | root.personal.events            | events    |
|  7 |       1 | root.personal.events.janaury    | january   |
|  8 |       1 | root.project.objective          | objective |
|  9 |       1 | root.personal.events.february   | february  |
| 10 |       1 | root.project.objective.january  | january   |
| 11 |       1 | root.project.objective.february | february  |
+----+---------+---------------------------------+-----------+

I thought that it might be easier to first order the results, and remove the top level from the path return. Using;

select id, name, subpath(path, 1) as path, nlevel(subpath(path, 1)) as level from testLtree order by level, path

I get;

+----+-----------+----------------------------+-------+
| id |   name    |            path            | level |
+----+-----------+----------------------------+-------+
|  3 | personal  | personal                   |     1 |
|  4 | project   | project                    |     1 |
|  1 | test      | test                       |     1 |
|  6 | events    | personal.events            |     2 |
|  5 | idea      | project.idea               |     2 |
|  8 | objective | project.objective          |     2 |
|  2 | inbox     | test.inbox                 |     2 |
|  9 | february  | personal.events.february   |     3 |
|  7 | january   | personal.events.january    |     3 |
| 11 | february  | project.objective.february |     3 |
| 10 | january   | project.objective.january  |     3 |
+----+-----------+----------------------------+-------+

I'm hoping to be able to transform this result into a set of JSON data somehow. I would like an output similar to this;

personal: {
    id: 3,
    name: 'personal',
    children: {
        events: {
            id: 6,
            name: 'events',
            children: {
                january: {
                    id: 7,
                    name: 'january',
                    children: null
                },
                february: {
                    id: 9,
                    name: 'february',
                    children: null
                }
            }
        }
    }
},
project: {
    id: 4,
    name: 'project',
    children: {
        idea: {
            id: 5,
            name: 'idea',
            children: null
        },
        objective: {
            id: 8,
            name: 'objective',
            children: {
                january: {
                    id: 10,
                    name: 'january',
                    children: null
                },
                february: {
                    id: 11,
                    name: 'february',
                    children: null
                }
            }
        }
    }]
},
test: {
    id: 1,
    name: 'test',
    children: {
        inbox: {
            id: 2,
            name: 'inbox',
            children: null
        }
    }
}

I've been looking around for the best way to do this but haven't came across any solutions that make sense to me. However, as I am new to postgres and SQL in general this is expected.

I think I may have to use a recursive query ? I'm a bit confused over what the best method/execution of this would be. Any help/advice is much appreciated! and any further questions please ask.

---

I've put everything into a sqlfiddle below;

http://sqlfiddle.com/#!17/1713e/5

Answer 1

I ran into the same problem as you. I had a large struggle with this in PostgreSQL and it became overly complex to solve. Since I'm using Django (Python framework), I decided to solve it using Python. In case it can help anyone in my same situation, I would like to share the code: https://gist.github.com/eherrerosj/4685e3dc843e94f3ef8645d31dbe490c