PSR-16 Support

  • Since 2.8.0

PSR-16 provides a simplified approach to cache access that does not involve cache pools, tags, deferment, etc.; it can be thought of as a key/value storage approach to caching.

zend-cache provides PSR-16 support via the class Zend\Cache\Psr\SimpleCache\SimpleCacheDecorator. This class implements PSR-16's Psr\SimpleCache\CacheInterface, and composes a Zend\Cache\Storage\StorageInterface instance to which it proxies all operations.

Instantiation is as follows:

use Zend\Cache\StorageFactory;
use Zend\Cache\Psr\SimpleCache\SimpleCacheDecorator;

$storage = StorageFactory::factory([
    'adapter' => [
        'name'    => 'apc',
        'options' => [],
    ],
]);

$cache = new SimpleCacheDecorator($storage);

Once you have a SimpleCacheDecorator instance, you can perform operations per that specification:

// Use has() to determine whether to fetch the value or calculate it:
$value = $cache->has('someKey') ? $cache->get('someKey') : calculateValue();
if (! $cache->has('someKey')) {
    $cache->set('someKey', $value);
}

// Or use a default value:
$value = $cache->get('someKey', $defaultValue);

When setting values, whether single values or multiple, you can also optionally provide a Time To Live (TTL) value. This proxies to the underlying storage instance's options, temporarily resetting its TTL value for the duration of the operation. TTL values may be expressed as integers (in which case they represent seconds) or DateInterval instances. As examples:

$cache->set('someKey', $value, 30); // set TTL to 30s
$cache->set('someKey', $value, new DateInterval('P1D'); // set TTL to 1 day

$cache->setMultiple([
    'key1' => $value1,
    'key2' => $value2,
], 3600); // set TTL to 1 hour
$cache->setMultiple([
    'key1' => $value1,
    'key2' => $value2,
], new DateInterval('P6H'); // set TTL to 6 hours

For more details on what methods are exposed, consult the CacheInterface specification.

Serialization

PSR-16 has strict requirements around serialization of values. This is done to ensure that if you swap one PSR-16 adapter for another, the new one will be able to return the same values that the original adapter saved to the cache.

Not all cache backends support the same data types, however. zend-cache provides a plugin, Zend\Cache\Storage\Plugin\Serializer, that you can attach to adapters in order to ensure data is serialized to a string when saving to the cache, and deserialized to native PHP types on retrieval. The following adapters require this plugin in order to work with the SimpleCacheDecorator:

  • Dba
  • Filesystem
  • Memcache
  • MongoDB
  • Redis
  • XCache

We provide a number of examples of attaching plugins to storage adapters in the plugins chapter. Generally, it will be one of:

// Manual attachment after you have an instance:
$cache->addPlugin(new Serializer());

// Via configuration:
$cache = StorageFactory::factory([
    'adapter' => 'filesystem',
    'plugins' => [
        'serializer',
    ],
]);

Deleting items and exceptions

PSR-16 states that the delete() and deleteMultiple() methods should return false if an error occured when deleting the key(s) provided, but true otherwise.

Generally, zend-cache storage adapters comply with this. However, it is possible to configure your adapter such that you may get a false positive result from these methods.

When an exception is raised and caught during key removal by an adapter, the adapter triggers an event with a Zend\Cache\Storage\ExceptionEvent. Plugins can react to these, and even manipulate the event instance. One such plugin, Zend\Cache\Storage\Plugin\ExceptionHandler, has a configuration option, throw_exceptions that, when boolean false, will prevent raising the exception. In such cases, adapters will typically return a boolean false anyways, but custom, third-party adapters may not.

Additionally, if you add a custom plugin that listens to removal event exceptions and modifies the return value and/or disables throwing the exception, a false positive return value could occur.

As such, we recommend that if you wish to use zend-cache to provide a PSR-16 adapter, you audit the plugins you use with your adapter to ensure that you will get consistent, correct behavior for delete() and deleteMultiple() operations.

Found a mistake or want to contribute to the documentation? Edit this page on GitHub!