From 74875b79af450a3569c10e3b6f25e8d57cda1846 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Andr=C3=A9=20Menrath?= Date: Wed, 6 Mar 2024 19:17:54 +0100 Subject: [PATCH] start writing documentation on how to write new event transformers --- transformer.md | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 81 insertions(+) create mode 100644 transformer.md diff --git a/transformer.md b/transformer.md new file mode 100644 index 0000000..91e6540 --- /dev/null +++ b/transformer.md @@ -0,0 +1,81 @@ +# Write a specialized ActivityPub transformer for an Event Custom Post Type + +> **_NOTE:_** This documentation is also likely to be userfu for other types other than events. + +The ActivityPub plugin offers a basic support for all post types out of the box, but it also allows the registration of external transformers. A transformer is a class that implements the [abstract transformer class](https://github.com/Automattic/wordpress-activitypub/blob/fb0e23e8854d149fdedaca7a9ea856f5fd965ec9/includes/transformer/class-base.php) and is responsible for generating the ActivityPub JSON representation of an WordPress post or comment. + +## Hooks + +To make the WordPress ActivityPub plugin use our custom transformer we simply add a filter to the `activitypub_transformer` hook which provides access to the transformer factory. The [transformer factory](https://github.com/Automattic/wordpress-activitypub/blob/master/includes/transformer/class-factory.php#L12) determines which transformer is used to transform a WordPress object to ActivityPub. + +```php +function register_custom_transformer_for_my_post_type( $transformer, $wp_object, $object_class ) { + // Return a custom transformer, if the WordPress object is a post and the post type matches. + if ( 'WP_Post' === $object_class && $wp_object->post_type === 'my_event_post_type' ) { + require_once __DIR__ . '/includes/activitypub/transformer/class-my-custom-transformer.php'; + return new My_Event_Post_Type_Transformer( $wp_object ); + } + return $transformer; // Return the default transformer. +} + +add_filter( + 'activitypub_transformer', + 'register_custom_transformer_for_my_post_type', + 10, + 3 +) +``` + +> **_NOTE:_** issues could arrise if this filter gets applied multiple times, be sure to take the priority argument of the `add_filter` into account. + +## Writing an event transformer class + +If you are writing a transformer for your custom post type it is recommended to start by extending the upstream generic [post transformer](https://github.com/Automattic/wordpress-activitypub/blob/fb0e23e8854d149fdedaca7a9ea856f5fd965ec9/includes/transformer/class-post.php). It contains useful default implementations for generating the [attachments](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-attachment), rendering a proper [content](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-content) in HTML from either blocks or the classic editor, extracting [tags](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-tag) and more. + +```php +/** + * ActivityPub Transformer for my_event_post_type. + */ +class My_Event_Post_Type_Transformer extends Activitypub\Transformer\Post; { +``` + +The main function which controls the transformation is `to_object`. This one is called by the ActivityPub plugin to get the resulting ActivityPub representation as an PHP-array. The convertion to json takes place later and you don't need to cover that. + +```php +/** + * Transform the WordPress Object into an ActivityPub Event Object. + * + * @return Activitypub\Activity\Extended_Object\Event + */ +public function to_object() { + $activitypub_object = new Activitypub\Activity\Extended_Object\Event(); + $activitypub_object = $this->transform_object_properties( $activitypub_object ); + + return $activitypub_object; +} +``` + + +### How to add new properties + +### How to customize the JSON-LD context + + + +### Mandatory properties + +#### type +```php + /** + * Returns the ActivityStreams 2.0 Object-Type for an Event. + * + * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-event + * @return string The Event Object-Type. + */ + protected function get_type() { + return 'Event'; + } +``` + +#### +