WP REST API: Order posts by meta value (acf)?

Question

I'm requesting posts with the WP REST API and need to sort them according to an ACF field. It's value represents a date (numeric, jQuery date format yymmdd). I know how to do it with a normal WP_Query and tried to do the same using the rest api:

mydomain.com/wp-json/wp/v2/posts?filter[orderby]=meta_value_num&filter[meta_key]=my_field_name&filter[order]=DESC

In fact I'm using a custom post type that's registered with the rest api and everything else is working perfectly, so I think its not a cpt specific issue?

But the posts show up in default order (their creation date, latest to oldest). What am I missing? Is this orderby parameter not supported by the rest api? If so, how can I implement it myself?

Any other workarounds, suggestions? Really looking for a solution! Thankful for any hints!

Answer 1

I'm guessing you haven't exposed meta_key and meta_value to the REST API with the rest_query_vars filter, so this should do it:

function my_add_meta_vars ($current_vars) {
    $current_vars = array_merge ($current_vars, array ('meta_key', 'meta_value'));
    return $current_vars;
}
add_filter ('rest_query_vars', 'my_add_meta_vars');

Then you can refer to meta_key and meta_value in your query.

Be aware that this obviously exposes all your post metadata to the API, which has potential security implications; I believe that's why it's not activated by default.

Answer 2

add_filter( 'rest_post_query', function (  $args, $request ) {
    if ( isset( $request['meta_key']) && !empty($request['meta_key'] ) ) {
        $args['meta_key'] = $request['meta_key'];
    }
    return $args;
}, 10, 2);

add_filter( "rest_post_collection_params", function($query_params, $post_type){

    array_push($query_params['orderby']['enum'],'meta_value' );

    return $query_params;
}, 10, 2);