How to resolve a recursive nested tree in jsonb? - json

Question

So I have a flattened tree like this:
[{
aid: "id3"
atype: ""
data: ["id1", "id2"]
},
{
aid: "id1"
atype: ""
data: ["id3", "id2"]
},
{
aid: "id2"
atype: ""
bdata: {aid: "id4", atype: "nested", data: ["id1", "id3"]}
data: []
}]
I want to gather that tree and resolve ids into data with recursion loops into something like this (say we start from "id3"):
{
aid: "id3"
payload: "1"
data: [
"id1":{
aid: "id1"
atype: ""
data: ["id3":Null, "id2":Null]
},
"id2":{
aid: "id2"
atype: ""
bdata: {aid: "id4", atype: "nested", data: ["id1":Null, "id3":Null]}
data: []
}]
}
So that we would get breadth-first search and resolve some field into "value": "object with that field" on first entrance and "value": Null
So How can one implement such a list to a tree in Postgres JSONb\ JSON?
I understand one could do it using something like PL/Python yet I failed to see a PL/Python function example that could do such a thing as not putting all JSON records into ram...
{'id1': {'aid': 'id1', 'atype': '', 'data': ['id3', 'id2']},
'id2': {'aid': 'id2',
'atype': '',
'bdata': {'aid': 'id4', 'atype': 'nested', 'data': ['id1', 'id3']},
'data': []},
'id3': {'aid': 'id3', 'atype': '', 'data': ['id1', 'id2']}}
Is not really usable for me - So I need a real tree.

Answer 1

There is a problem with your approach.
Let's consider following json.
{
"aid": "id3",
"atype": "",
"data": ["id1", "id2"]
},
{
"aid": "id4",
"atype": "",
"data": ["id1", "id2"]
}
Here, id1 and id2 data need to be copied again for id4, It creates lot of duplicate data.
Instead of that, convert your data to dictionary.
You can access the data just by calling the id’s like “id1”, “id2” and so on.
data_map = {}
for data in data_array:
data_map.__setitem__(data['aid'], data)
Following will be sample output.
{
"id3": {
"aid": "id3",
"atype": "",
"data": [
"id1", "id2"
]
}
This way you can access the id’s directly and don’t have duplicates in the structure.
Complete sample code
import json
json_data = '''
[
{
"aid": "id3",
"atype": "",
"data": ["id1", "id2"]
},
{
"aid": "id1",
"atype": "",
"data": ["id3", "id2"]
},
{
"aid": "id2",
"atype": "",
"bdata": {"aid": "id4", "atype": "nested", "data": ["id1", "id3"]},
"data": []
}
]
'''
data_array = json.loads(json_data)
data_map = {}
for data in data_array:
data_map.__setitem__(data['aid'], data)
print(data_map)