Non-destructive JSON encoding/decoding of associative PHP arrays (containing objects)

Question

I am able to JSON encode and decode indexed arrays in a way that the decoded value matches the original input:

$array_indexed = ['A'];
$encoded = json_encode($array_indexed); 
$decoded = json_decode($encoded);
var_dump($array_indexed);
array(1) {
  [0]=>
  string(1) "A"
}
var_dump($decoded);
array(1) {
  [0]=>
  string(1) "A"
}

However when I encode an associate array, I end up with an object:

$array_associate = [ 'FOO' => 'BAR'];
$encoded = json_encode($array_associate);
$decoded = json_decode($encoded);
var_dump($array_associate);
array(1) {
  ["FOO"]=>
  string(3) "BAR"
}
var_dump($decoded);
object(stdClass)#1 (1) {
  ["FOO"]=>
  string(3) "BAR"
}

My understanding is that this is normal behaviour since Javascript doesn't support associate arrays, which are represented instead using objects, hence when encoding an associating array, it ends up encoded as an object (and therefore decoded as such).

Q1: Do you confirm?

Possible solutions

serialize /unserialize:
The reason for absolutely wanting to use json_encode/json_decode over serialize /unserialize is that the encoded form is much more concise, which is important because it ends up stored in cache and cache space is limited:

var_dump(json_encode(['A'=>1,'B'=>2])); // string(13) "{"A":1,"B":2}"
var_dump(serialize(['A'=>1,'B'=>2])); //   string(30) "a:2:{s:1:"A";i:1;s:1:"B";i:2;}

Q2: Have you ever been confronted with cache space issues using serialize, and if so how did you address is other than by using json_encode(I'm thinking compression, but if value is to end up in a MySQL DB cache I'm a bit uneasy with it)?

json_decode($json,true):
The problem is that nested objects that should remain objects are also converted to arrays:

$obj = new stdClass;
$obj->foo = 'bar';
$array_associate = [ 'A' => $obj];
$encoded = json_encode($array_associate);
var_dump(json_decode($encoded,true));
array(1) {
  ["A"]=>
  array(1) {     <---------------- NO LONGER AN OBJECT, DON'T WANT THAT
    ["foo"]=>
    string(3) "bar"
  }
}

convert object of objects to array of objects:

Still based on the above example

$object_of_objects = json_decode($encoded);
$array = [];
foreach($object_of_objects as $key=>$object) {
    $array[$key] = $object;
}
var_dump($array);
array(1) {                
  ["A"]=>
  object(stdClass)#6 (1) {
    ["foo"]=>
    string(3) "bar"
  }
}

Q3: Do you see any other solution to convert associate array of objects to JSON and back while preserving original input?

Thanks but I knew that already (see "The problem is that nested objects that should remain objects are also converted to arrays" in question). — Max Corbeau
– Max Corbeau, Commented Oct 23, 2012 at 17:41
Your question is soooo extreeeemly long so I didn't notice that :) I think there are other PHP libraries that can create json. Probably look there (sorry I have no link / name on top of my head). — hakre
– hakre, Commented Oct 23, 2012 at 18:11
That's true it's long, maybe I should aim at being more concise some times. — Max Corbeau
– Max Corbeau, Commented Oct 23, 2012 at 18:23

hakre · Accepted Answer · 2012-10-23 10:01:14Z

4

As it is not possible to write an associate array in json, it will be written as an object, and thus PHP will reed it as an object when you decode it.

In order to make PHP read it as an array you have to set the second parameter of json_decode to true:

json_decode($json, true)
                   ^^^^

edited Oct 23, 2012 at 10:01

hakre

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answered Oct 23, 2012 at 9:58

Zlug

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2 Comments

Max Corbeau Over a year ago

Thanks but I knew that already (see "The problem is that nested objects that should remain objects are also converted to arrays").

Zlug Over a year ago

Well, in that case json is not your answer

Rijk · Accepted Answer · 2012-10-23 09:57:36Z

2

Q1: yes, PHP associative 'arrays' (which are actually not arrays strictly speaking) are converted to Javascript objects when translated to JSON. Why is this a problem for you?

Q2: I would use JSON over serialized, not only because it's more concise but also because it's more widely supported, and doesn't have issues when using UTF-8 encoded text.

If you do not want json_decode() to convert the JS objects to arrays, set the second parameter to false.

Question (not meaning to sound harsh): why are you so hung up on objects over arrays? It's quite easy to work with the latter in PHP, even in DB abstraction layers like PDO.

answered Oct 23, 2012 at 9:57

Rijk

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2 Comments

Max Corbeau Over a year ago

json_decode() with second parameter set to false isn't ideal with associative arrays of objects: as shown in the question, the associate array itself is converted to an object (so when I use phpUnit to compare values before inserting to and after retrieving from cache, assertEquals gives me errors. As for your question, I'm not hung up on objects , I just found them more readable than arrays (I prefer $obj->value over $obj['value']).

Chris Harrison Over a year ago

In my case I'm not "hung up" on objects. I'm storing Wordpress post objects - so when I retrieve them they need to be in object format. Arrays would be impossible to work with. But I also need to store an array of these objects so that I can foreach over them with minimum fuss. At the moment json_encode is converting the whole array of objects into an "object of objects". By the way, I found that serialize works perfectly for this although the resulting cache file that I'm writing to is longer. It's also unreadable but as this is just a cache file, that shouldn't be a problem.

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