So on Manager layer,it is just DbUserManager to focus on creating or destroying the DbUser object(creatUser()&deleteUser())

On Database layer,it is just DbUser to operate on database.

Yes,you are right.In DbUserManager deleteUser(),it directly operate on the database.It is not a good design.

Suggest to move deleteUser() to DbUser class.

Before this DbUser object was remove from Cache,this method should be invoked.

我的建议是将数据库操作全部移至DbUserManager中，这样方便封装数据库操作，做DAO，方便数据库移植。否则DbUser,DbUserManager都要做DAO,太麻烦。