Recursive function to create hierarchical JSON object?

Question

I\'m just not a good enough computer scientist to figure this out by myself :(

I have an API that returns JSON responses that look like this:

// call to         


        

Answer 1

Disclaimer : I have no idea what json is about, so you may have to sort out how to write it correctly in your language :p. If the pseudo-code in my example is too pseudo, feel free to ask more details.

You need to return something somewhere. If you never return something in your recursive call, you can't get the reference to your new objects and store it in the objects you have where you called the recursion.

def getChildNodes (node) returns [array of childNodes]
    data = getData(fromServer(forThisNode))
    new childNodes array
    for child in data :
        new temp_obj
        temp_obj.stores(child.interestingStuff)
        for grandchild in getChildNodes(child) :
            temp_obj.arrayOfchildren.append(grandchild) 
        array.append(temp_obj)
    return array

Alternatively, you can use an iterator instead of a return, if your language supports it.

Answer 2

You could use this (a more compact and readable version)

def get_child_nodes(node_id):   
    request = urllib2.Request(ROOT_URL + node_id)
    response = json.loads(urllib2.urlopen(request).read())
    return {
       "id":response['id'],
       "name":response['name'],
       "children":map(lambda childId: get_child_nodes(childId), response['childNode'])
    }

get_child_nodes(ROOT_NODE)

Answer 3

def get_node(node_id):   
    request = urllib2.Request(ROOT_URL + node_id)
    response = json.loads(urllib2.urlopen(request).read())
    temp_obj = {}
    temp_obj['id'] = response['id']
    temp_obj['name'] = response['name']
    temp_obj['children'] = [get_node(child['id']) for child in response['childNode']]
    return temp_obj

hierarchy = get_node(ROOT_NODE)

Answer 4

You're not returning anything from each call to the recursive function. So, it seems like you just want to append each temp_obj dictionary into a list on each iteration of the loop, and return it after the end of the loop. Something like:

def get_child_nodes(node_id):   
    request = urllib2.Request(ROOT_URL + node_id)
    response = json.loads(urllib2.urlopen(request).read())
    nodes = []
    for childnode in response['childNode']:
        temp_obj = {}
        temp_obj['id'] = childnode['id']
        temp_obj['name'] = childnode['name']
        temp_obj['children'] = get_child_nodes(temp_obj['id'])
        nodes.append(temp_obj)
    return nodes

my_json_obj = json.dumps(get_child_nodes(ROOT_ID))

(BTW, please beware of mixing tabs and spaces as Python isn't very forgiving of that. Best to stick to just spaces.)

Answer 5

I had the same problem this afternoon, and ended up rejigging some code I found online.

I've uploaded the code to Github (https://github.com/abmohan/objectjson) as well as PyPi (https://pypi.python.org/pypi/objectjson/0.1) under the package name 'objectjson'. Here it is below, as well:

Code (objectjson.py)

import json

class ObjectJSON:

  def __init__(self, json_data):

    self.json_data = ""

    if isinstance(json_data, str):
      json_data = json.loads(json_data)
      self.json_data = json_data

    elif isinstance(json_data, dict):
      self.json_data = json_data

  def __getattr__(self, key):
    if key in self.json_data:
      if isinstance(self.json_data[key], (list, dict)):
        return ObjectJSON(self.json_data[key])
      else:
        return self.json_data[key]
    else:
      raise Exception('There is no json_data[\'{key}\'].'.format(key=key))

  def __repr__(self):
    out = self.__dict__
    return '%r' % (out['json_data'])

Sample Usage

from objectjson import ObjectJSON

json_str = '{ "test": {"a":1,"b": {"c":3} } }'

json_obj = ObjectJSON(json_str)

print(json_obj)           # {'test': {'b': {'c': 3}, 'a': 1}}
print(json_obj.test)      # {'b': {'c': 3}, 'a': 1}
print(json_obj.test.a)    # 1
print(json_obj.test.b.c)  # 3