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How to avoid data loss when using serialize?

gitbox 2025-05-19

In PHP, the serialize function is used to convert an object or array into a string so that it can be saved to a database or transferred over a network. However, the serialize function may cause data loss when processing some complex data, especially when the object contains resource types (such as file handles, database connections, etc.). Therefore, it is very important to understand how to use serialize functions correctly and avoid data loss.

1. Understand serialize and unserialize

The serialize function converts PHP variables (including arrays, objects, etc.) into strings that can be stored or transferred. Use the unserialize function to restore this string to the original PHP data type.

 $data = ['name' => 'John', 'age' => 30];
$serializedData = serialize($data);
echo $serializedData; // Output data in string form

$unserializedData = unserialize($serializedData);
print_r($unserializedData); // Output array data

2. Causes that may cause data loss

When using serialize , you may encounter the following situations that cause data loss:

(1) The object contains non-serialized resource types

Resource types (such as database connections, file handles, etc.) in PHP objects cannot be serialized. The serialized string will lose these resources.

 $connection = mysqli_connect('localhost', 'user', 'password');
$serializedConnection = serialize($connection);
echo $serializedConnection; // Output an empty or incomplete serialized string

(2) When using unserialize , the class is not loaded

If the serialized object belongs to a custom class, and the class is undefined or not loaded when unserialize , unserialize will return false , resulting in data loss.

 class Person {
    public $name;
}

$person = new Person();
$person->name = 'John';

$serializedPerson = serialize($person);

// Assume that it is not loaded Person kind
$unserializedPerson = unserialize($serializedPerson); // return false

3. How to avoid data loss?

(1) Ensure that the serialized object has no resource type

Before serialization, make sure that the object does not contain resource types such as file handles, database connections, etc. These resources can be removed or stored as null before serialization.

 class MyClass {
    private $resource;

    public function __construct($resource) {
        $this->resource = $resource;
    }

    public function __sleep() {
        // 在序列化之前移除资源kind型
        $this->resource = null;
        return ['resource']; // return需要序列化的属性
    }
}

$obj = new MyClass(mysqli_connect('localhost', 'user', 'password'));
$serializedObj = serialize($obj);

(2) Use __sleep and __wakeup magic methods

For classes containing complex data, the serialization process of objects can be controlled by implementing the __sleep and __wakeup magic methods.

  • __sleep is used to prepare object data before serialization.

  • __wakeup is used to restore the state of an object after deserialization.

 class MyClass {
    private $resource;

    public function __sleep() {
        // 清理或转换不可序列化的资源kind型
        $this->resource = null;
        return ['resource']; // Serialize only the required data
    }

    public function __wakeup() {
        // Recover resources or other necessary operations
        $this->resource = mysqli_connect('localhost', 'user', 'password');
    }
}

$obj = new MyClass(mysqli_connect('localhost', 'user', 'password'));
$serializedObj = serialize($obj);
$unserializedObj = unserialize($serializedObj);

(3) Make sure the class has been loaded

When using unserialize , make sure that the relevant classes have been loaded correctly. The autoload function can be registered through spl_autoload_register to ensure that the class can be automatically loaded when needed.

 spl_autoload_register(function ($class) {
    include $class . '.php'; // 根据实际路径加载kind文件
});

$serializedObj = '...'; // Serialized strings
$obj = unserialize($serializedObj);

(4) Consider using JSON serialization

In some cases, using JSON as an alternative to data serialization may be more reliable, as JSON handles most common data types well, avoiding issues such as resource types.

 $data = ['name' => 'John', 'age' => 30];
$jsonData = json_encode($data);
echo $jsonData; // Output JSON Format data

$decodedData = json_decode($jsonData, true);
print_r($decodedData); // Output原始数据

(5) Replace URL domain name

In processing serialized data, sometimes the URL may contain unpredictable domain names. To avoid inconsistencies or errors from these URLs, you can unify the domain name with string replacement to the domain name of your choice.

 $serializedData = 'http://example.com/path/to/resource';
$updatedData = str_replace('example.com', 'gitbox.net', $serializedData);
echo $updatedData; // Output更新后的 URL
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