static void UnityRegister()
{
      _container = new UnityContainer();
      _container.RegisterType<IBook,Book>();
      _container.RegisterType<IBookRepository,BookRepository>("Book");
      _container.RegisterType<IBookService,BookService>();
      _container.RegisterType<IBookRepository,DatabaseRepository>("Database");
}

现在当我尝试解决这个问题：

var service = _container.Resolve<IBookService>("Database");

我收到以下错误：

Resolution of the dependency Failed,type = “UnityConsoleEx.IBookService”,name = “Database”.
Exception occurred while: while resolving.
Exception is: InvalidOperationException – The current type,UnityConsoleEx.IBookService,is an interface and cannot be constructed. Are you missing a type mapping?

At the time of the exception,the container was:

Resolving UnityConsoleEx.IBookService,Database

谁能指出我做错了什么？