Instant Articles for WP (Wordpress plugin) Selectively discard posts from feed

Question

I'm trying to automatically exclude all articles that don't have a custom field set. I have checked the 'instant_articles_before_render_post' and 'instant_articles_after_render_post' hooks but I wonder how I could use them to prevent the render of the article. Any ideas?

Answer 1

instant_articles_before_render_post and instant_articles_after_render_post are used to launch actions before / after the post rendering but cannot prevent the post to render. What you need to do is to hook on pre_get_posts in order to change the main query used by Facebook Instant Articles.

If you look in the facebook-instant-articles.php plugin file, you will see the following function:

function instant_articles_query( $query ) {
    if ( $query->is_main_query() && $query->is_feed( INSTANT_ARTICLES_SLUG ) ) {
        $query->set( 'orderby', 'modified' );
        $query->set( 'posts_per_page', 100 );
        $query->set( 'posts_per_rss', 100 );
        /**
         * If the constant INSTANT_ARTICLES_LIMIT_POSTS is set to true, we will limit the feed
         * to only include posts which are modified within the last 24 hours.
         * Facebook will initially need 100 posts to pass the review, but will only update
         * already imported articles if they are modified within the last 24 hours.
         */
        if ( defined( 'INSTANT_ARTICLES_LIMIT_POSTS' ) && INSTANT_ARTICLES_LIMIT_POSTS ) {
            $query->set( 'date_query', array(
                array(
                    'column' => 'post_modified',
                    'after'  => '1 day ago',
                ),
            ) );
        }
    }
}
add_action( 'pre_get_posts', 'instant_articles_query', 10, 1 );

You can hook right after this and add your own meta condition like this:

function instant_articles_query_modified($query) {
    if($query->is_main_query() && isset(INSTANT_ARTICLES_SLUG) && $query->is_feed(INSTANT_ARTICLES_SLUG)) {
        $query->set('meta_query', array(
            array(
                  'key' => 'your_required_meta'
            )
        ));
}
add_action('pre_get_posts', 'instant_articles_query_modified', 10, 2);