Question

我有课程Student和Class。

public class Student : ApplicationUser
{
    public DateTime DateBorn     { get; set; }
    public virtual ICollection<Class> Classes { get; set; }
}

public class Class
{
    public int Id { get; set; }
    public int CourseId { get; set; }
    public Course Course { get; set; }
    public string ProfessorId { get; set; }
    public Professor Professor { get; set; }
    public short Size { get; set; }
    public int Year { get; set; }
    public Term Term { get; set; }
    public bool Enrollable { get; set; }
    public virtual ICollection<Student> Students { get; set; }
}

我正在尝试获取Classes注册的Student。我想过在方法class.Students.Contains()中使用方法.Where()，但它给我一个例外。

// GET: Classes/Calendar
public async Task<ActionResult> Calendar(int? year, Term? term)
{
    year = year ?? DateTime.Now.Year;
    term = term ?? (Term)(DateTime.Now.Month / 4);

    var student = await UserManager.FindByIdAsync(User.Identity.GetUserId());

    var classes = db.Classes
                .Where(c => c.Students.Contains(student) && c.Year == year && c.Term == term);

    return View(await classes.ToListAsync());
}

例外：Unable to create a constant value of type 'Demosthenes.Core.Models.Student'. Only primitive types or enumeration types are supported in this context.

如何在不必编写显式连接的情况下正确执行此操作？

Answer 1

如果Student的主键属性为Id且User.Identity.GetUserId()返回类型与Student::Id相同，则可以尝试此操作。

var id = User.Identity.GetUserId();
var classes = db.Classes
   .Where(c => c.Students.Any(s => s.Id == id) 
               && c.Year == year && c.Term == term);

Answer 2

您需要退后一步并更改表格结构。

对于多对多关系，您需要在中间添加联结表，例如

Student
StudentClass
Class

您的代码将成为

var classes = db.Classes
            .Where(c => c.StudentClasses
                         .Any(x=>x.StudentId == student.Id) 
                     && c.Year == year && c.Term == term);

.Net MVC 5查询与ApplicationUser具有多对多关系的模型

2 个答案: