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

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