Convert JSON categories tree to database table - json

Question

Imagine I have a categories tree like this JSON file:
[
{
"id": "1",
"text": "engine",
"children": [
{
"id": "2",
"text": "exhaust",
"children": []
},
{
"id": "3",
"text": "cooling",
"children": [
{
"id": "4",
"text": "cooling fan",
"children": []
},
{
"id": "5",
"text": "water pump",
"children": []
}
]
}
]
},
{
"id": "6",
"text": "frame",
"children": [
{
"id": "7",
"text": "wheels",
"children": []
},
{
"id": "8",
"text": "brakes",
"children": [
{
"id": "9",
"text": "brake calipers",
"children": []
}
]
},
{
"id": "10",
"text": "cables",
"children": []
}
]
}
]
How can I convert it to this flat table?
id parent_id text
1 NULL engine
2 1 exhaust
3 1 cooling
4 3 cooling fan
5 3 water pump
6 NULL frame
7 6 wheels
8 6 brakes
9 8 brake calipers
10 6 cables
I found similar questions and inverted questions (from table to JSON) but I can't figure it out with jq and its #tsv filter. Also I noticed the "flatten" filter is not often referenced in the answers (while it looks to be the exact tool I need) but it might be because it was introduced recently in the latests versions of jq.

Answer 1

Here is another solution which uses jq's recurse builtin:
["id","parent_id","text"]
, (
.[]
| recurse(.id as $p| .children[] | .parent=$p )
| [.id, .parent, .text]
)
| #tsv
Sample Run (assumes filter in filter.jq and sample data in data.json)
$ jq -Mr -f filter.jq data.json
id parent_id text
1 engine
2 1 exhaust
3 1 cooling
4 3 cooling fan
5 3 water pump
6 frame
7 6 wheels
8 6 brakes
9 8 brake calipers
10 6 cables
Try it online!

Answer 2

The key here is to define a recursive function, like so:
def children($parent_id):
.id as $id
| [$id, $parent_id, .text],
(.children[] | children($id)) ;
With your data, the filter:
.[]
| children("NULL")
| #tsv
produces the tab-separated values shown below. It is now easy to add headers, convert to fixed-width format if desired, etc.
1 NULL engine
2 1 exhaust
3 1 cooling
4 3 cooling fan
5 3 water pump
6 NULL frame
7 6 wheels
8 6 brakes
9 8 brake calipers
10 6 cables

Answer 3

Here is a solution which uses a recursive function:
def details($parent):
[.id, $parent, .text], # details for current node
(.id as $p | .children[] | details($p)) # details for children
;
["id","parent_id","text"] # header
, (.[] | details(null)) # details
| #tsv # convert to tsv
Sample Run (assumes filter in filter.jq and sample data in data.json)
$ jq -Mr -f filter.jq data.json
id parent_id text
1 engine
2 1 exhaust
3 1 cooling
4 3 cooling fan
5 3 water pump
6 frame
7 6 wheels
8 6 brakes
9 8 brake calipers
10 6 cables
Try it online!