我开始构建一个插件，其中需要使用wpdb 对象这是我第一次使用它。所以我查看了如何使用它。我看了一些例子，有一件事让我很困惑：upgrade.php

实际上，当我创建一个自定义查询时，只有当我包含upgrade.php 这样做：

require_once( ABSPATH . \'wp-admin/includes/upgrade.php\' );
$custom_posts = $wpdb->get_results( \'SELECT * FROM \' . self::TABLE . \'\', OBJECT_K );
$wpdb->show_errors();
echo $wpdb->last_query;
return $custom_posts;

有什么用upgrade.php ? 我的意思是，如果我不把它放进去，查询就不起作用了。请有人解释一下，因为法典中没有这方面的内容。

我真的有义务使用它吗？为什么？怎样

谢谢

更新：这里是完整的代码。

/**
 * On activate or uninstall plugin
 */
register_activation_hook( __FILE__, array( \'Cpt\', \'init\' ) );
register_deactivation_hook( __FILE__, array( \'Cpt\', \'uninit\' ) );
register_uninstall_hook( __FILE__, array( \'Cpt\', \'uninit\' ) );

global $wpdb;

class Cpt
{

    CONST TABLE = \'cpt\';

    /**
     * Constructor
     */
    public function init()
    {
        /**
         * Creation table for cpt
         */
        $sql = "CREATE TABLE IF NOT EXISTS `" . self::TABLE . "` (
          id mediumint(9) NOT NULL AUTO_INCREMENT,
          time datetime DEFAULT \'0000-00-00 00:00:00\' NOT NULL,
          name tinytext NOT NULL,
          UNIQUE KEY id (id)
        );";
        require_once( ABSPATH . \'wp-admin/includes/upgrade.php\' );
        $wpdb->query($sql);

        self::convert_to(\'post\', \'custom\');
    }

    public function uninit() {
        /**
         * Delete table for cpt
         */
        require_once( ABSPATH . \'wp-admin/includes/upgrade.php\' );
        //$wpdb->query("DROP TABLE IF EXISTS `cpt`;");
        //$this->delete_cpt("Custom post 1");
    }

    /**
     * Add a custom post type
     */
    public function add_cpt($name) {
        /**
         * Add a single data
         */
        $time = (string)date(\'dmY\');
        require_once( ABSPATH . \'wp-admin/includes/upgrade.php\' );
        $wpdb->insert( 
            self::TABLE, 
            array(
                \'time\'=>$time, 
                \'name\'=>$name
            ) 
        );
        /*$wpdb->show_errors();
        echo $wpdb->last_query;
        die();*/
    }

    /**
     * Delete a custom post type
     */
    public function delete_cpt($name) {
        /**
         * delete a single data
         */
        require_once( ABSPATH . \'wp-admin/includes/upgrade.php\' );
        $wpdb->delete( 
            self::TABLE, 
            array( 
                \'name\'=>$name 
            ) 
        );
        $wpdb->show_errors();
        echo $wpdb->last_query;
        die();
    }

    /**
     * Get all custom post types
     */
    public static function get_ctps() {
        /**
         * delete a single data
         */
        require_once( ABSPATH . \'wp-admin/includes/upgrade.php\' );
        $custom_posts = $wpdb->get_results( \'SELECT * FROM \' . self::TABLE . \'\', OBJECT_K );
        $wpdb->show_errors();
        echo $wpdb->last_query;
        return $custom_posts;
    }

    /**
     * Get a single custom post type
     */
    public function get_ctp($name) {
        /**
         * get a single data
         */
        require_once( ABSPATH . \'wp-admin/includes/upgrade.php\' );
        $custom_post = $wpdb->get_results( \'SELECT name FROM \' . self::TABLE . \' WHERE name = $name\', OBJECT_K );
        $wpdb->show_errors();
        echo $wpdb->last_query;
        print_r($custom_post);
        //return $custom_post;
    }

    /**
     * Post type conversion
     */
    public static function convert_to($from, $to) {

        // Get the posts of the type $from
        require_once( ABSPATH . \'wp-admin/includes/upgrade.php\' );
        $wpdb->update( \'wp_posts\', array(\'post_type\'=>$to), array(\'post_type\'=>$from) );
        $wpdb->show_errors();
        echo $wpdb->last_query;
    }

    /**
     * Generate admin menu with all custom post types
     */
    public function generate_menu() {

        $custom_posts = self::get_ctps(); 
    }
}