xPheRe xPheRe - 5 years ago 209
PHP Question

Error serializing an object tree with SplObjectStorage

I have implemented a simple Composite pattern using SplObjectStorage, like the example above:

class Node
{
private $parent = null;

public function setParent(Composite $parent)
{
$this->parent = $parent;
}
}

class Composite extends Node
{
private $children;

public function __construct()
{
$this->children = new SplObjectStorage;
}

public function add(Node $node)
{
$this->children->attach($node);
$node->setParent($this);
}
}


Whenever I try to serialize a Composite object, PHP 5.3.2 throws me a
Segmentation Fault
.
This only happens when I add any number of nodes of any type to the object.

This is the offending code:

$node = new Node;
$composite = new Composite;
$composite->add($node);
echo serialize($composite);


Although this one works:

$node = new Node;
$composite = new Composite;
echo serialize($composite);


Also, if I implement the Composite pattern with array() instead of SplObjectStorage, all runs ok too.

What I'm making wrong?

Answer Source

By setting the Parent, you have a circular reference. PHP will try to serialize the composite, all of it's nodes and the nodes in turn will try to serialize the composite.. boom!

You can use the magic __sleep and __wakeup() methods to remove (or do whatever to the) the parent reference when serializing.

EDIT:

See if adding these to Composite fixes the issue:

public function __sleep()
{
    $this->children = iterator_to_array($this->children);
    return array('parent', 'children');
}
public function __wakeup()
{
    $storage = new SplObjectStorage;
    array_map(array($storage, 'attach'), $this->children);
    $this->children = $storage;
}
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