How to amend WordPress REST endpoint queries

Getting Started

The rest_{$post_type}_query filter helps you ammend the query parameters of any REST enabled post type, plus attachments. The filter function takes two parameters:

• $args: the arguments array that will passed on to the WordPress query
• $request: the REST request, including any parameters passed in by the URL

The $args array is formatted the same as a WP_Query args array (because it will eventually be used in one. This means you can augment the $args array with any valid options that WP_Query accepts

Example

Let’s say we want to support passing in meta_query and taxonomy_query values when querying posts. We’re going to assume the passed in values are JSON encoded meta/tax_query values, so all we need to do is the following:

<?php
add_filter('rest_post_query', function($args, $request) {
	if(isset($request['meta_query'])) {
		$meta_query = json_decode($request['meta_query'], true);

		if($meta_query !== null) {
			$args['meta_query'] = $meta_query;
		}
	}

	if(isset($request['tax_query'])) {
		$tax_query = json_decode($request['tax_query'], true);
		
		if($meta_query !== null) {
			$args['tax_query'] = $tax_query;
		}
	}
});

First we check if the $request parameter includes meta/tax_query options. In this case we’ve passed in fully JSON encoded queries. Next, we ensure decoding works and if so, we add meta/tax_query values to our $args array.

Note: The true parameter in json_decode creates an associative array (versus an object), which is required to be valid in a WP_Query instance.