Question

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));

这在我看来

@{ 
    //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>
    }

}
}

每次ViewBag.Enrollments = registerDB.Carts.Where(x => x.Username.Equals(User.Identity.Name));都没有返回任何结果时，我收到错误提示System.InvalidOperationException: There is already an open DataReader associated with this Command which must be closed first.并且此行突出显示

if (timeSlot == item.Workshop.TimeSlot)

Answer 1

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();

Answer 2

在尝试使用之前，您正在检查item != null但不是item.Workshop != null。看起来这可能是错误，但为什么它会提升InvalidOperationException而不是NullReferenceException我不知道。

尝试：

if (item != null && item.Workshop != null)
{
    if (timeSlot == item.Workshop.TimeSlot)
    {
        <h3>@timeSlot</h3>
    }
}

Answer 3

你能把单一电话放在你的模型中吗？

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

然后在你的控制器中设置ViewBag：

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

条款中的MVC3多条件

3 个答案: