Caching

Cache

Concrete CMS uses cache to store data for quicker future retrieval.

Object Caching

Concrete uses a PSR-6 compatible caching layer with three default pools:

• cache: The primary, ephemeral cache, typically in-memory or using a fast caching driver. It's configurable via concrete.cache.levels.object.
• cache/request: An ephemeral, single-request cache, replacing the CacheLocal API.
• cache/expensive: For performance-benefiting, slow cache items, generally on disk. It's loaded into ephemeral cache on access for faster subsequent use within the same request. Its drivers are configurable via concrete.cache.levels.expensive.

Basic API – Retrieving and Setting Items

Using the Object Cache

Example: Retrieving a "StudentList" object:

public static function getByCourseID($id)
{
    $expensiveCache = \Core::make('cache/expensive');
    $studentCourseList = $expensiveCache->getItem('StudentList/Course' . $id);
    if ($studentCourseList->isMiss()) {
        $studentCourseList->lock();
        $list = StudentList::findBy(array('course_id' => $id));
        $expensiveCache->save($studentCourseList->set($list)->expiresAfter(300)); // expire after 300 seconds
    } else {
        $list = $studentCourseList->get();
    }
    return $list;
}

This code caches 'StudentList/Course{$id}' in the expensive cache, fetching from the database if not found and adding it to the cache.

Notes

• Deeply nested cache items can create extensive directory structures.
• Be cautious of file path length limits on certain file systems.

Handling the Blackhole Cache

To avoid issues when the cache is disabled (using a 'BlackHole' cache), ensure $value always contains the desired data:

$expensiveCache = \Core::make('cache/expensive');
$cacheObject = $expensiveCache->getItem('Cache/MyObject');
if ($cacheObject->isMiss()) {
    $value = $this->lookupSomeValue();
    $expensiveCache->save($cacheObject->set($value));
} else {
    $value = $cacheObject->get();
}
echo $value;

Clearing the Cache

To invalidate a cache, for example, when a new student joins a course:

public addStudentToCourse($studentId, $courseId)
{
    // Add student to the course code
    $expensiveCache = \Core::make('cache/expensive');
    $studentCourseList = $expensiveCache->getItem('StudentList/Course' . $courseId);
    $studentCourseList->clear();
}

Cache invalidation also occurs when a user clears the cache via the dashboard.