REST API Changes in 5.4

Taxonomy “OR” Relation Now Supported in Posts Controller

Querying for /wp/v2/posts?tags=1&categories=2 returns all posts assigned the tag with ID 1, AND assigned the category with ID 2. This AND relationship, where multiple taxonomies’ term relationships must all be satisfied, has been the only supported behavior in these collection endpoints since WordPress 4.7.

The REST API /wp/v2/posts endpoint, as well as custom post type endpoints extending from WP_REST_Posts_Controller (including custom post types specifying "show_in_rest" => true), now supports a new tax_relation parameter which can be used to return posts matching either taxonomy filter, rather than both.

As an example, in WordPress 5.4, the posts endpoint query


will now return posts in either the tag ID 1 or the category with ID 2.

Selective Link Embedding

The REST API now supports returning a limited set of embedded objects using the _embed parameter. As an example, in WordPress 5.4, the following query only embeds the author information instead of including all the comments, media, etc…


All embeds will be returned if a value for the _embed parameter is omitted, or set to true or 1.

WP_REST_Server method changes

WordPress 5.4 changes the signature of two methods in the WP_REST_Server class. Developers who are extending WP_REST_Server and overriding these methods should update their code to match the new signatures to avoid PHP warnings.

  1. The signature of WP_REST_Server::embed_links() is now embed_links( $data, $embed = true ). The new $embed paramter accepts an array of link relations (such as array( 'author', 'wp:term' )) and limits the embedded links in the response to those relations. The default of true maintains the previous behavior of embedding all links in the response. For more details, see #39696.
  2. The signature of WP_REST_Server::get_routes() is now get_routes( $namespace = '' ). The new $namespace parameter accepts a string and limits the returned routes to those whose namespace matches the string. Internally, WP_REST_Server uses this new parameter to improve the performance of WP_REST_Server::dispatch() by reducing the number of regex checks necessary to match a request to a registered route. For more details, see #48530.

For performance reasons, WP_REST_Server::embed_links() also now caches response data in memory. This cache is managed by WP_REST_Server::response_to_data(). Code calling the protected embed_links method being called directly may need to be updated to ensure stale data is not returned.

(Thank you to @dlh for authoring this section)

See the full list of REST API changes on Trac.

#5-4, #dev-notes, #rest-api