c# - LINQ to Entities 仅支持转换实体数据模型基元类型？

Question

我正在尝试在我的 View 中填充下拉菜单。任何帮助是极大的赞赏。谢谢。

错误:

Unable to cast the type 'System.Int32' to type 'System.Object'.

LINQ to Entities only supports casting Entity Data Model primitive types.

Controller :

ViewBag.category = (from c in new IntraEntities().CategoryItems
                   select new SelectListItem() {Text=c.Name, Value=""+c.ID }).ToList<SelectListItem>();

查看:

Category:<br />@Html.DropDownList("category", (List<SelectListItem>)ViewBag.category)

Answer 1

这个怎么样:

ViewBag.category = 
    from c in new IntraEntities().CategoryItems.ToList()
    select new SelectListItem 
    {
        Text = c.Name, 
        Value = c.ID.ToString() 
    };

以及如何使用强类型 View 模型而不是 ViewBag 的一些弱类型废话(我就是这样调用它的)？

像这样:

public class CategoryViewModel
{
    public string CategoryId { get; set; }
    public IEnumerable<SelectListItem> Categories { get; set; }
}

然后:

public ActionResult Foo()
{
    var model = new CategoryViewModel
    {
        Categories = 
            from c in new IntraEntities().CategoryItems.ToList()
            select new SelectListItem 
            {
                Text = c.Name, 
                Value = c.ID.ToString() 
            }
    };
    return View(model);
}

最后在您的强类型 View 中:

@model CategoryViewModel
@using (Html.BeginForm())
{
    @Html.DropDownListFor(x => x.CategoryId, Model.Categories)
    <button type="submit">OK</button>
}

好多了，你不觉得吗？