事情是这样的，写了个实例，
配置了'DB_PREFIX' => 'ev_', // 数据库表前缀
定义了一个Model，
更改了这个Model对应的数据表名
protected $tableName = "sys_user";
但是，我dump这个Model的实例，发现是这样：
["pk":protected] => string(2) "id"
["autoinc":protected] => bool(true)
["tablePrefix":protected] => string(3) "ev_"
["name":protected] => string(4) "User"
["dbName":protected] => string(0) ""
["connection":protected] => string(0) ""
["tableName":protected] => string(0) ""
["trueTableName":protected] => string(7) "ev_user"
["error":protected] => string(0) ""
["fields":protected] => array(7) {
....................
点解？