PHP Serialization and Inheritance [duplicate]

Question

Not sure what the process is for serializing a child class that is implementing the Serializable interface, the parent class no longer retains the data it was once serializing. Is there a step I am missing?

class A {
    private $aVar = "test";
}

class B extends A implements Serializable {
    private static $bVar = "tset";

    public function serialize() {
        return serialize(self::$bVar);
    }
    public function unserialize($serialized) {
        self::$bVar = unserialize($serialized);
    }
}

$s = serialize(new B());
$u = unserialize($s);

What I am actually trying to do is create a static variable in the child class, but since serialization does not handle static variables, I was attempting to serialize just this myself; here, i'll go ahead and change that on here now so better reflects the scenario. Maybe the title should be how to serialize a static variable in a child class? — NueFox
– NueFox, Commented Nov 1, 2017 at 12:36

giolliano sulit · Accepted Answer · 2017-11-01 05:56:36Z

1

I think you're a bit confused as to what's happening here, but essentially what you're seeing is incorrectly scoped variables.

Public variables, are variables that are visible to all classes
Private variables, are variables that are visible only to the class to which they belong.
Protected variables, are variables that are visible only to the class to which they belong, and any subclasses.

If you were to make $aVar in Class A protected or public you'd be able to access it in Class B:

You would get the following:

B Object
(
    [bVar:B:private] => tset
    [aVar] => test
)

answered Nov 1, 2017 at 5:56

giolliano sulit

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1 Comment

NueFox Over a year ago

but I don't want to access it; if I were to remove the Serializable interface and corresponding the methods, everything is serialized perfectly fine.

Black Mantha · Accepted Answer · 2025-02-03 16:12:03Z

Serializing a static doesn't really make sense, so I changed that to a non-static in my answer:

You're supposed to implement Serializable in the parent class as well:

class A implements Serializable
{
  public function __construct(private $aVar) {}
  public function serialize() {
    return serialize($this->aVar);
  }
  public function unserialize($serialized) {
    $this->aVar = unserialize($serialized);
  }
}

class B extends A implements Serializable
{
  public function __construct($aVar, private $bVar) {
    parent::__construct($aVar);
  }
  public function serialize() {
    return serialize([$this->bVar, parent::serialize()]);
  }
  public function unserialize($serialized) {
    $arr = unserialize($serialized);
    $this->bVar = $arr[0];
    parent::unserialize($arr[1]);
  }
}

$obj = new B('aVal', 'bVal');
$ser = serialize($obj);
echo $ser . "\n";
var_export(unserialize($ser));

C:1:"B":44:{a:2:{i:0;s:4:"bVal";i:1;s:11:"s:4:"aVal";";}}
B::__set_state(array(
   'aVar' => 'aVal',
   'bVar' => 'bVal',
))

If you can't do that, you will have to use reflection to get and set the value of aVar from B. That's not an elegant solution, though.

And I know this is an old question, but the Serializable interface is deprecated, you should use __serialize() and __unserialize() instead. This work much the same way, just remove the interface, and you don't need to call \serialize()/\unserialize() in your methods. Also, all classes must serialize as arrays:

// in class A:
  public function __serialize() {
    return [$this->aVar];
  }
  public function __unserialize($serialized) {
    list($this->aVar) = $serialized;
  }

// in class B:
  public function __serialize() {
    return [$this->bVar, parent::__serialize()];
  }
  public function __unserialize($serialized) {
    $this->bVar = $serialized[0];
    parent::__unserialize($serialized[1]);
  }

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