全局变量在功能内部不起作用

Question

在WordPress插件中我有此代码

 $country_table = $wpdb->prefix . "trackbyid_country";
 $cities_table  = $wpdb->prefix . "trackbyid_cities";
 function database_creation(){
    global $wpdb;
    global $country_table;
    global $cities_table;
    $AO_name = "trackbyid_dbv";
    $AO_value = "1";
    add_option($AO_name, $AO_value);
    $charset_collate = $wpdb->get_charset_collate();
    $sql = "CREATE TABLE $country_table (
        id mediumint(9) NOT NULL AUTO_INCREMENT,
        time datetime DEFAULT '0000-00-00 00:00:00' NOT NULL,
        country tinytext NOT NULL,
        PRIMARY KEY  (id)
        ) $charset_collate;";
    require_once ( ABSPATH . 'wp-admin/includes/upgrade.php');
    dbDelta($sql);
    $sql = "CREATE TABLE $cities_table(
        id mediumint(9) NOT NULL AUTO_INCREMENT,
        time datetime DEFAULT '0000-00-00 00:00:00' NOT NULL,
        city tinytext NOT NULL,
        country_id mediumint(9) NOT NULL,
        city_latitude mediumint(9) NOT NULL,
        city_longitude mediumint(9) NOT NULL,
        PRIMARY KEY  (id)
        ) $charset_collate;";
     dbDelta($sql);

 }

我认为我的问题（没有创建数据库）与全局$ country_table和$ cities_table变量有关。当我将这些变量作为本地问题时，问题就解决了！我的全局变量声明和用法有什么问题？

Answer 1

您的变量$country_table和$cities_table无法定义，因为在尝试在这些var中使用它之前，您没有在全局$ wpdb中引入。改用此方法：

global $wpdb;
$country_table = $wpdb->prefix . "trackbyid_country";
$cities_table  = $wpdb->prefix . "trackbyid_cities";
function database_creation(){
    global $country_table, $cities_table;
    ...
}