Adds Module taxonomy colum to lessons list and adds it to quick edit

add-course-module-to-lesson-admin.php

<?php
/**
 * Makes the module column in the admin's lesson list sortable.
 * 
 * @package     DeWittePrins\CoreFunctionality\SenseiLMS
 * @since       1.7.1
 * @author      Hans Schuijff
 * @link        https://dewitteprins.nl
 * @license     GNU-2.0+
 */
namespace DeWittePrins\CoreFunctionality\SenseiLMS;

add_filter( 'register_taxonomy_args', __NAMESPACE__ . '\correct_module_taxonomy_args', 20, 3 );
/**
 * Enhance the registration of Sensei Module taxonomy to:
 * - show modules in quick edit (this will enable bulk edits)
 * - show modules in REST api (needed for quick edit)
 * - show modules in posts list
 * - add missing labels
 * 
 * Normally setting show_admin_column to true, 
 * will setup wordpress to show the column automatically in admins post list screen
 * However in case of Sensei LMS the columns in that screen are hardcoded 
 * and overwrite the default behaviour.
 * 
 * @since  1.7.1
 * @param  array  $args
 * @param  string $taxonomy
 * @return array  $args
 */
function correct_module_taxonomy_args( $args, $taxonomy ) {
  
    if ( function_exists( 'Sensei' ) && 'module' === $taxonomy ) {

        if ( ! isset( $args['labels']['view_item'] ) ) {
            $args['labels']['view_item']     = __( 'View Module', 'sensei-lms' );
        }        
        if ( ! isset( $args['labels']['back_to_items'] ) ) {
            $args['labels']['back_to_items'] = __( '← Back to Modules', 'sensei-lms' );
        }        

        $args['show_admin_column']       = true;
        $args['show_in_quick_edit']      = true;
        $args['show_in_rest']            = true;
    }

    return $args;
}

add_filter( 'manage_edit-lesson_sortable_columns', __NAMESPACE__ . '\set_module_column_to_sortable_in_lessons_list' );
/**
 * Makes the lesson-module column sortable in admins post list
 * 
 * This only tells wordpress the column is sortable.
 * It also needs to learn how to sort on that column, 
 * so the query must be programmed too to sort on this taxonomy
 *  
 * @since  1.7.1
 * @param  array $columns
 * @return array $columns
 */
function set_module_column_to_sortable_in_lessons_list( $columns ) {

    $columns['taxonomy-module'] = 'taxonomy-module';

    return $columns;
}

add_filter( 'posts_clauses', __NAMESPACE__ . '\add_clause_to_order_lessons_by_module', 10, 2 );
/**
 * Tells wordpress how to sort lessons by lesson module
 * 
 * Adds an order by clause to the query 
 * whenever the orderby query var is set to "lesson-module"
 * 
 * This teaches wordpress how to sort the admin post list of lessons
 * on lesson-module
 * 
 * @since  1.7.1
 * @param  array  $clauses
 * @return object $wp_query instance of WP_Query
 */
function add_clause_to_order_lessons_by_module( $clauses, $wp_query ) {
    global $wpdb;
    
    if ( isset( $wp_query->query['orderby'] ) 
    && 'taxonomy-module' == $wp_query->query['orderby'] ) {
        $clauses['join'] .= 
            " LEFT JOIN (
                SELECT object_id, GROUP_CONCAT(name ORDER BY name ASC) AS module
                FROM $wpdb->term_relationships
                INNER JOIN $wpdb->term_taxonomy USING (term_taxonomy_id)
                INNER JOIN $wpdb->terms USING (term_id)
                WHERE taxonomy = 'module'
                GROUP BY object_id
            ) AS module_terms ON ($wpdb->posts.ID = module_terms.object_id)";
        $clauses['orderby'] = 'module_terms.module ';
        $clauses['orderby'] .= ( 'ASC' == strtoupper( $wp_query->get('order') ) ) ? 'ASC' : 'DESC';
    }
    
    return $clauses;
}