Using a Setter with Multidimensional Arrays - php

Question

I'm trying to create a __set for an object in PHP that works with multidimensional arrays. Is this even possible?
I would like to be able to something like the following: $post->comments[0]['uid']=3;. However, comments is actually going to be a key in a private cache variable $_cache['comments']=array(). It'd be nice if the __set function could somehow get both the base key (comments) and the index (0) as well as the key/value it is setting (uid/3). However, that's not possible.
I've thought about making $_cache['comments'] and array of ArrayObjects but that wouldn't let me define a custom _get/_set overload. Instead, I think that I might end up having to create a new Comments object and then fill the array with those. However, I really wouldn't like to do this and it'd be sweet if somehow PHP could handle nested arrays in __set overloads.
I'm using Mongo and would like if I could just have one single object for each document. However, arrays objects in Mongo are creating a bit of a problem for me. I would like to just handle them as an array in PHP but that doesn't seem possible. The setter needs to take $post->comments[0]['uid']=3 and update both the cache as well as setting $this->data['comments'][0]['uid']=3.
I know that if comments was an array of objects I could do this:
$post->comments[0]->uid=3;
///Sets $_cache['comments'][0]->uid=3;
And it would work because the getter for comments would return the array of objects and allow it to access the uid property. I could then have a getter/setter within the comments object that would somehow edit the $post->data through a pseudo "friend" function/hack. However, I don't see an easy way of accomplishing this with arrays....
Any advice?

Answer 1

That's more complex than you actually imagine. You can accomplish what you want with a heap of workarounds, but it's seldomly worth the effort.
If ->comments itself is resolved by a getter method, than assigning something to the [0] subarray won't actually end up in the private property. And ->comments[0]= will not even invoke your setter method. Instead this is a read access.
To make this work at all you would have to make your __get method return an reference of & $this->_cache['comments'].
If you want to intercept set accesses in that comments array you would indeed need ArrayObject. The difference is that this requires to override offsetGet and offsetSet instead of __get and __set. But again, since you are accessing a further subarray, the __get method will actually be used and you need to return another reference, or yet again a level of ArrayObject workaround goo.

Answer 2

I jumped through some of these hoops when building my own PHP wrapper class.
https://github.com/gatesvp/MongoModel
It's still in the the works, but it does handle some basic "map this object to DB".

Answer 3

There's virtually nothing worthwhile written in PHP chat rooms or the php documentation that's going to be useful to you, Adam. Most of the suggestions tend along the lines of implementing interface ArrayAccess or extending class ArrayObject, both in the SPL. In fact, there is a surprisingly straightforward solution to your problem: $post->comments[0]['uid']=3 using overloaded setter __set().
Define private $comments = array(); in class post. For convenience, use a text key for the first subscript of $comments: here, integer 0 becomes, say, "zero". You then invoke the setter as follows:
$post->zero = ['uid', 3];
This invokes the magic setter because there is no publicly declared property $zero in class post: "The overloading methods are invoked when interacting with properties or methods that have not been declared or are not visible in the current scope." (PHP 5 man page on Overloading.)
The setter can also be setComments(), a convenience because you won't have to discriminate among incoming properties to identify those intended for array comments, but the calling syntax becomes less natural.
Your overloaded, auto-magical function __set receives two arguments: a property and a value:
public function __set($property, $value) {
very reminiscent of Crockford's JSON protocol. It is helpful to think of it in those terms.
Since property "zero" that you sent in does not exist in classpost, it needs to be trapped, and my preferred method, since the first subscript in property comments will likely have several values, is to define a private array of supported subscript values in post:
private $indices = [
"zero" => 0,
"one" => 1,
"two" => 2,
"three" => 3
];
When the index for comments arrives in __set() as $property, it is verified to exist in $indices. Now you simply iterate through the array supplied in $value, extract
uid and its corresponding value, then assign to $comments as follows:
public function __set($property, $value) {
if (array_key_exists($property, $this->indices) && is_array($value))
foreach ($value as $uid => $uid_value)
$this->comments[$this->indices[property]][$uid] = $uid_value;
else
...
}
with $this->indices[property] being used to extract the integer value 0 to be used to
index the first dimension of comments, and $uid_value extracted with value int 3 to be assigned.
The approach outlined here is not a gimmick, workaround or clever trick. It's a straightforward design technique intended to work with one of SPL's facilities and can, in principle, be extended to arrays of arbitrary dimension. I have the design implemented in a production system so, if you're still having difficulty, post here and I'll help you to debug your application. Best of luck!

Answer 4

I believe the closest you can do for overloading some properties is to use the magic method __set() defined here: http://us.php.net/__set
I am not sure you can handle the [0] before it gets taken by the PHP compiler...
So your other solution would be to transform comments into a method
public function comments($id) {
return $this->obj[$id]; // Obj
}
And the object you return has the __set property
class Obj {
private $id;
public function __set($key, $value) {
if($key === 'uid') {
$_cache = $GLOBALS['_cache'];
$_cache['comments'][$this->id]->uid = $value;
}
}
}
There is a lot of code missing here, but you can figure out how to do it with this __set method()

Answer 5

Create a function instead of trying to hack it on top of something that isn't even meant for that.
public function setCommentUid($commentId, $uid) {
$this->_cache['comments'][$commentId]->uid = $uid;
}
//then...
$post->setCommentUid(0, 3);
This makes it much simpler to use the class and it's much easier to see what it does.