Commit c4286466 authored by alexpott's avatar alexpott

Issue #2444211 by Wim Leers, jhodgdon: Document cacheability of render arrays,...

Issue #2444211 by Wim Leers, jhodgdon: Document cacheability of render arrays, and the considerations to use when generating render arrays
parent 89e6ec9f
......@@ -162,7 +162,6 @@
* removing them).
* @section assets Assets
* We can distinguish between three types of assets:
* 1. unconditional page-level assets (loaded on all pages where the theme is in
* use): these are defined in the theme's *.info.yml file.
......@@ -287,9 +286,56 @@
* properties. Look through implementations of hook_element_info() to discover
* elements defined this way.
* @section sec_attached Attaching libraries in render arrays
* @section sec_caching Caching
* The Drupal rendering process has the ability to cache rendered output at any
* level in a render array hierarchy. This allows expensive calculations to be
* done infrequently, and speeds up page loading. See the
* @link cache Cache API topic @endlink for general information about the cache
* system.
* In order to make caching possible, the following information needs to be
* present:
* - Cache keys: Identifiers for cacheable portions of render arrays. These
* should be created and added for portions of a render array that
* involve expensive calculations in the rendering process.
* - Cache contexts: Contexts that may affect rendering, such as user role and
* language. When no context is specified, it means that the render array
* does not vary by any context.
* - Cache tags: Tags for data that rendering depends on, such as for
* individual nodes or user accounts, so that when these change the cache
* can be automatically invalidated. If the data consists of entities, you
* can use \Drupal\Core\Entity\EntityInterface::getCacheTags() to generate
* appropriate tags; configuration objects have a similar method.
* - Cache max-age: The maximum duration for which a render array may be cached.
* Defaults to \Drupal\Core\Cache\Cache::PERMANENT (permanently cacheable).
* Cache information is provided in the #cache property in a render array. In
* this property, always supply the cache contexts, tags, and max-age if a
* render array varies by context, depends on some modifiable data, or depends
* on information that's only valid for a limited time, respectively. Cache keys
* should only be set on the portions of a render array that should be cached.
* Contexts are automatically replaced with the value for the current request
* (e.g. the current language) and combined with the keys to form a cache ID.
* The cache contexts, tags, and max-age will be propagated up the render array
* hierarchy to determine cacheability for containing render array sections.
* Here's an example of what a #cache property might contain:
* @code
* '#cache' => [
* 'keys' => ['entity_view', 'node', $node->id()],
* 'contexts' => ['language'],
* 'tags' => ['node:' . $node->id()],
* 'max-age' => Cache::PERMANENT,
* ],
* @endcode
* At the response level, you'll see X-Drupal-Cache-Contexts and
* X-Drupal-Cache-Tags headers.
* See for
* details.
* @section sec_attached Attaching libraries in render arrays
* Libraries, JavaScript settings, feeds, HTML <head> tags and HTML <head> links
* are attached to elements using the #attached property. The #attached property
* is an associative array, where the keys are the attachment types and the
......@@ -303,14 +349,13 @@
* values. Example:
* @code
* $build['#attached']['library'][] = 'core/jquery';
* $build['#attached']['drupalSettings']['foo] = 'bar';
* $build['#attached']['drupalSettings']['foo'] = 'bar';
* $build['#attached']['feed'][] = ['aggregator/rss', $this->t('Feed title')];
* @endcode
* See drupal_process_attached() for additional information.
* @section render_pipeline The Render Pipeline (or: how Drupal renders pages)
* First, you need to know the general routing concepts: please read
* @ref sec_controller first.
......@@ -382,7 +427,6 @@
* when an error occurs, a simpler HTML page renderer is used for rendering
* these bare pages: \Drupal\Core\Render\BareHtmlPageRenderer
* @see themeable
* @}
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