Asp.net mvc 3 MVC3 where子句中的多个条件

我的控制器中有以下内容

var workshop = registerDB.Workshops.Single(w => w.WorkshopID == id);
ViewBag.Enrollments = registerDB.Carts.Where(x => x.Username.Equals(User.Identity.Name));

在我看来

@{ 
    //var carts = Model.Carts.Where(x => x.Username.Equals(User.Identity.Name));
     var carts =  ViewBag.Enrollments;
     var timeSlot = Model.TimeSlot;
    }

   @{
foreach (var item in carts)

{
    if (item != null)
    {
    if (timeSlot == item.Workshop.TimeSlot)
    {
        <h3>@timeSlot</h3>
    }
    }
     else
    {
        <h3>Does not Exist</h3>
    }

}
}

尝试在控制器中调用

.ToList（）

，以急切地获取结果：

ViewBag.Enrollments = registerDB
    .Carts
    .Where(x => x.Username.Equals(User.Identity.Name))
    .ToList();

---

您正在检查

项！=空

但不是该

item.Workshop！=在尝试使用它之前为空。这可能就是错误所在，但我不知道为什么它会引发
invalidooperationexception
而不是
NullReferenceException

尝试：

if（item！=null&&item.Workshop！=null）
{
if（时隙==项目.车间.时隙）
{
@时隙
}
}
您能在您的模型中加入单个调用吗：

workshops workshop = registerDB.Workshops.Single(w => w.WorkshopID == id);

然后在控制器中设置ViewBag：

try
{
ViewBag.Enrollments = workshop.Carts.Where(x => x.Username.Equals(User.Identity.Name));
}
catch
{
ViewBag.Enrollments = "There are no results";
}

@Edgaroching'-不确定。如果用户没有做出任何选择，如何检查ViewBag.Enrollments是否已注册？
workshops workshop = registerDB.Workshops.Single(w => w.WorkshopID == id);

try
{
ViewBag.Enrollments = workshop.Carts.Where(x => x.Username.Equals(User.Identity.Name));
}
catch
{
ViewBag.Enrollments = "There are no results";
}