json_encode() on a multidimensional array - with string keys

Question

I am creating an very large multidimensional array using PHP. Each object contains Name, ID, ParentID and Children. Children is an array of more objects in the same format.

It is critical I name the IDs of each object - this helps me put each object under the correct parent. (In the code below, I use 101, 102 etc.)

However, the problem I am having is when I return the array in JSON using json_encode. Each 'Children' array is being printed as an object, not an array - as shown in the JSON code below.

As I read on another SO thread here, they "are made as objects because of the inclusion of string keys" - although they are numbers, they are still strings.

{
"101": {
 "ID": "101",
 "ParentID": "0",
 "Name": "Root One"
 "Children": {
 "102": {
 "ID": "102",
 "ParentID": "101",
 "Name": "Child One"
 },
 "103": {
 "ID": "103",
 "ParentID": "101",
 "Name": "Child Two",
 "Children": {
 "104": {
 "ID": "104",
 "ParentID": "103",
 "Name": "Child Child One"
 }
 }
 },

Does anyone know how to overcome this issue?

Edit: The JSON should look like this (the square brackets are important!):

[
{
 "ID": "101",
 "ParentID": "0",
 "Name": "Root One",
 "Children": [
 {
 "ID": "102",
 "ParentID": "101",
 "Name": "Child One",
 "Children": [

• Ja͢ck: It's actually because the indices are not contiguous, i.e. there are gaps.
• STT LCU: Also, your "children" ARE objects (from my perspective) and not arrays. Be glad, and let OOP flow within you.

Answer 1

A JSON array has no explicit indexes, it's just an ordered list. The only JSON data structure that has named keys is an object. The literal should make this quite obvious:

["foo", "bar", "baz"]

This array has no named indices and there isn't any provision to add any.

PHP conflates both lists and key-value stores into one array data type. JSON doesn't.

• mohammad mohsenipur: associative array has named keys
• deceze: @mohammad PHP has "associative arrays", JSON doesn't! JSON's "associative arrays" are called objects.
• Patrick: Thanks, the issue I was having was the structure of the JSON (see my last edit). The problem was caused due to the named keys in my PHP associative array.

Answer 2

This is your object:

$parent=new StdClass();
$parent->ID=101;
$parent->ParentID=0;
$parent->Name='Root One';
$child1=new StdClass();
$child1->ID=1011;
$child1->ParentID=$parent->ID;
$child1->Name='Child One';
$parent->Children[]=$child1;
$child1_1=new StdClass();
$child1_1->ID=10111;
$child1_1->ParentID=$child1->ID;
$child1_1->Name='Child One One';
$child1->Children[]=$child1_1; 

This is your JSON convert function:

echo json_encode($parent,JSON_PRETTY_PRINT);

and this is your object coded into JSON format:

{
 "ID": 101,
 "ParentID": 0,
 "Name": "Root One",
 "Children": [
 {
 "ID": 1011,
 "ParentID": 101,
 "Name": "Child One",
 "Children": [
 {
 "ID": 10111,
 "ParentID": 1011,
 "Name": "Child One One"
 }
 ]
 }
 ]
}

The answer came later because I started learning PHP later. Anyway, some day, someone might find it useful.

Answer 3

I have now got a working solution which is fast and works well.

1. Firstly, as written in SO link from the question;

   In JSON, arrays only have numeric keys, whereas objects have string properties. The inclusion of a array key forces the entire outer structure to be an object by necessity.

   In JSON; Curly braces hold objects ({}), Square brackets hold arrays ([]).

2. So using a string as a key will result in the json_encode function returning objects, whereas reseting the keys will ensure it creates arrays.

3. Therefore, just before I return my JSON encoded string, I run a function to reset all the array keys. The code I found on this SO thread (Reset array keys in multidimensional array) was particularly useful!

Answer 4

http://php.net/manual/en/function.json-decode.php

Set 2nd parameter of json_decode to true to atleast get assoc arrays.

Aside from that: javascript can't handle non-sequential/non-contiguous array indexes, so as soon as the id's are not sequential, json has no other option then to convert it into "string" indexes.

• Patrick: Thanks for your answer, it will no doubt be of use in the future, but I was using the returned JSON in jQuery!
• Damien Overeem: That hardly changes the fact that javascript can't handle non sequential array keys. Hence neither can JSON. And hence neither can jquery.
• Damien Overeem: A downvote without comment 1 year after this post.. one wonders why o.O