c# – 用于避免交换机语句的体系结构

在系统中,用户具有0..n角色.根据用户当前的角色,系统将向该用户返回一组特定数据.用户将能够执行某些操作,但不能执行其他操作等.

public?class?User
{
????public?bool?HasRole(string?roleName)
????{
????????return?this.UserRoles.Any(r?=>?r.Name?==?roleName);
????}

????public?string?Username?{?get;?set;?}

????public?long??CurrentRoleId?{?get;?set;?}
????public?Role?CurrentRole?{?get;?set;?}

????public?virtual?IList<Role>?UserRoles?{?get;?set;?}
}

public?class?Role
{
????public?Role()?{?}

????public?string?Name?{?get;?set;?}
}

public?class?GetEventsQuery?:?IQuery<List<Event>>
{
????public?List<Event>?Query()
????{
????????switch?(this.user.CurrentRole.Name)
????????{
????????????case?"Administrator":
????????????????UserIsNotInAdministratorRole();
????????????????return?repository.All.ToList();

????????????case?"Supervisor":
????????????????UserIsNotInSupervisorRole();
????????????????return?repository.All.Where(evnt?=>?evnt.SupervisorId?==?this.user.RecordId).ToList();

????????????case?"User":
????????????????UserIsNotInUserRole();
????????????????return?repository.All.Where(evnt?=>?evnt.UserId?==?this.user.RecordId).ToList();

????????????default:
????????????????throw?new?Exception("GetEventsQuery?Unknow?exception.");
????????}
????}

????private?void?UserIsNotInUserRole()
????{
????????if?(!this.user.HasRole("User"))
????????{
????????????throw?new?NoUserRoleException("User?does?not?have?user?role!");
????????}
????}

????private?void?UserIsNotInSupervisorRole()
????{
????????if?(!this.user.HasRole("Supervisor"))
????????{
????????????throw?new?NoSupervisorRoleException("User?does?not?have?supervisor?role!");
????????}
????}

????private?void?UserIsNotInAdministratorRole()
????{
????????if?(!this.user.HasRole("Administrator"))
????????{
????????????throw?new?NoAdministratorRoleException("User?does?not?have?administrator?role!");
????????}
????}

????public?GetEventsQuery(string?username,?IUserRepository?userRepository,?IEventRepository?repository)
????{
????????this.repository?=?repository;

????????var?userQuery?=?new?GetUserQuery(username,?userRepository);
????????this.user?=?userQuery.Query();
????}

????private?readonly?User?user;
????private?readonly?IEventRepository?repository;
}

此switch语句将显示在系统的所有部分中.如果有一种方法可以将它重新分解为一个类并将它放在一个单独的位置,我不介意保留它,但重复一遍又一遍肯定是代码味道.我刚刚开始这个项目,所以如果有更好的方法来设计对象层次结构或做出重大改变以消除这个问题,我愿意接受它.