asp.net-mvc-4 - 用于在 mvc4 中包含视图模型的指令

Question

我已经阅读了 MVC3 教程，用于在 asp.net 页面中显示相关数据。它有一个视图模型：

using System; 
using System.Collections.Generic; 
using ContosoUniversity.Models; 

namespace ContosoUniversity.ViewModels 
{ 
    public class InstructorIndexData 
    { 
        public IEnumerable<Instructor> Instructors { get; set; } 
        public IEnumerable<Course> Courses { get; set; } 
        public IEnumerable<Enrollment> Enrollments { get; set; } 
    }
}

和一个控制器，带有动作：

using ContosoUniversity.ViewModels;

public ActionResult Index(Int32? id, Int32? courseID) 
{ 
    var viewModel = new InstructorIndexData(); 
    viewModel.Instructors = db.Instructors 
                              .Include(i => i.OfficeAssignment) 
                              .Include(i => i.Courses.Select(c => c.Department)) 
                              .OrderBy(i => i.LastName); 

    if (id != null) 
    { 
        ViewBag.InstructorID = id.Value; 
        viewModel.Courses = viewModel.Instructors.Where(i => i.InstructorID ==         id.Value).Single().Courses; 
    } 

    if (courseID != null) 
    { 
        ViewBag.CourseID = courseID.Value; 
        viewModel.Enrollments = viewModel.Courses.Where(x => x.CourseID ==  courseID).Single   ().Enrollments; 
    } 

    return View(viewModel); 
}

当我在 MVC4 中尝试时，使用 ContosoUniversity.ViewModels；不存在

并且在

viewModel.Courses = viewModel.Instructors.Where(i => i.InstructorID ==            id.Value).Single().Courses; 

由于无法将 viewmodel.instructors 转换为IEnumerable<viewmodel.Instructors>