用户注册通用类，User类：

包含有两个私有属性：映射到WORX_USER表中USER_ID字段的$uid和映射到其余字段的数组变量$fields.他们可以通过重写的_get()和

_set()方法进行访问，但是为了防止对$uid的意外修改，保护了$uid.-Register generic type, User class: consists of two private properties: the table is mapped to WORX_USER USER_ID $ uid field in the rest of the field and mapped to the array variable $ fields. They can rewrite the _get () and _ set () method to access, but in order to prevent accidental changes to the $ uid, protected $ uid.