cache

The cache tag tells Twig to cache a template fragment:

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{% cache "cache key" %}
    Cached forever (depending on the cache implementation)
{% endcache %}

If you want to expire the cache after a certain amount of time, specify an expiration in seconds via the ttl() modifier:

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{% cache "cache key" ttl(300) %}
    Cached for 300 seconds
{% endcache %}

The cache key can be any string that does not use the following reserved characters {}()/\@:; a good practice is to embed some useful information in the key that allows the cache to automatically expire when it must be refreshed:

• Give each cache a unique name and namespace it like your templates;
• Embed an integer that you increment whenever the template code changes (to automatically invalidate all current caches);
• Embed a unique key that is updated whenever the variables used in the template code changes.

For instance, I would use {% cache "blog_post;v1;" ~ post.id ~ ";" ~ post.updated_at %} to cache a blog content template fragment where blog_post describes the template fragment, v1 represents the first version of the template code, post.id represent the id of the blog post, and post.updated_at returns a timestamp that represents the time where the blog post was last modified.

Using such a strategy for naming cache keys allows to avoid using a ttl. It's like using a "validation" strategy instead of an "expiration" strategy as we do for HTTP caches.

If your cache implementation supports tags, you can also tag your cache items:

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{% cache "cache key" tags('blog') %}
    Some code
{% endcache %}

{% cache "cache key" tags(['cms', 'blog']) %}
    Some code
{% endcache %}

The cache tag creates a new "scope" for variables, meaning that the changes are local to the template fragment:

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{% set count = 1 %}

{% cache "cache key" tags('blog') %}
    {# Won't affect the value of count outside of the cache tag #}
    {% set count = 2 %}
    Some code
{% endcache %}

{# Displays 1 #}
{{ count }}

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$ composer require twig/cache-extra

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$ composer require twig/extra-bundle

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use Twig\Extra\Cache\CacheExtension;

$twig = new \Twig\Environment(...);
$twig->addExtension(new CacheExtension());

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use Symfony\Component\Cache\Adapter\FilesystemAdapter;
use Symfony\Component\Cache\Adapter\TagAwareAdapter;
use Twig\Extra\Cache\CacheRuntime;
use Twig\RuntimeLoader\RuntimeLoaderInterface;

$twig->addRuntimeLoader(new class implements RuntimeLoaderInterface {
    public function load($class) {
        if (CacheRuntime::class === $class) {
            return new CacheRuntime(new TagAwareAdapter(new FilesystemAdapter()));
        }
    }
});