.. _cache-using-cache-tags:

Sometimes you need to create context-dependent variations of data that should be

cached. For example, the data used to render a dashboard page may be expensive

to generate and unique per user, so you can't cache the same data for everyone.

In such cases, Symfony allows you to create different cache contexts using

namespaces. A cache namespace is an arbitrary string that identifies a set of

related cache items. All cache adapters provided by the component implement the

:class:`Symfony\\Contracts\\Cache\\NamespacedPoolInterface`, which provides the

:method:`Symfony\\Contracts\\Cache\\NamespacedPoolInterface::withSubNamespace`

method.

This method allows you to namespace cached items by transparently prefixing their keys::

In this example, the cache item uses the ``dashboard_data`` key, but it will be

stored internally under a namespace based on the current user ID. This is handled

automatically, so you **don’t** need to manually prefix keys like ``user-27.dashboard_data``.

There are no guidelines or restrictions on how to define cache namespaces.

You can make them as granular or as generic as your application requires:

$flagCache = $cache->withSubNamespace(

$featureToggle->isEnabled('new_checkout') ? 'checkout-v2' : 'checkout-v1'

);

$channel = $request->attributes->get('_route')?->startsWith('api_') ? 'api' : 'web';

$channelCache = $cache->withSubNamespace($channel);

.. tip::

You can even combine cache namespaces with :ref:`cache tags <cache-using-cache-tags>`

for more advanced needs.

There is no built-in way to invalidate caches by namespace. Instead, the recommended

approach is to change the namespace itself. For this reason, it's common to include

static or dynamic versioning data in the cache namespace::