MVC3在where子句

我有我的控制器MVC3在where子句

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

以下多个条件，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));回报没有结果，我得到一个错误说System.InvalidOperationException: There is already an open DataReader associated with this Command which must be closed first.这行突出显示

if (timeSlot == item.Workshop.TimeSlot)

来源

2011-09-21 Masinde Muliro

尝试调用.ToList()在控制器中预先抓取结果：

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

来源

2011-09-21 10:14:46

我如何检查ViewBag.Enrollments在用户没有做出任何选择的情况下？ –

您检查item != null但不是item.Workshop != null尝试使用它之前。这似乎也许是错误，但为什么它提高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> 
    } 
}

来源

2011-09-21 10:15:16 ChrisF

我试过了，但仍然有相同的错误 –

@EdgarOchieng' - 不确定。 – ChrisF

你能不能把单一的呼叫模型：

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

然后在你的控制器设置ViewBag：

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

来源

2011-09-21 13:09:51

MVC3在where子句

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