Question

我的代码如下。当我运行它时，我得到了例外：

System.Data.Entity.dll中出现“System.NotSupportedException”类型的异常但未在用户代码中处理
附加信息：无法创建类型为“MvcApplication1.Models.QuantityPerUnit”的常量值。在此上下文中仅支持原始类型或枚举类型。“

似乎我无法使用List public static List<QuantityPerUnit> QuantityPerUnitItems = new List<QuantityPerUnit>。它应该用IEnumerable替换，但如果我使用IEnumerable它会显示同构错误：

System.Collections.Generic.IEnumerable'不包含'添加
的定义

代码：

namespace MvcApplication1.Models
{
    public class ProductEditViewModel : Product
    {
        // For DropDownListFor need IEnumerable<SelectListItem>
        public IEnumerable<SelectListItem> SupplierItems { get; set; }

        // For RadioButtonFor need below
        public Int32? CategorySelectedId { get; set; }
        public IEnumerable<Category> CategorieItems { get; set; }

        // For CheckBoxFor need below
        public string QuantityPerUnitSelectedId { get; set; }
        public IEnumerable<QuantityPerUnit> QuantityPerUnitItems { get; set; }
    }

    public class QuantityPerUnit
    {
        public string QuantityPerUnitId { get; set; }
        public string Quantity { get; set; }

        public static List<QuantityPerUnit> QuantityPerUnitItems = new List<QuantityPerUnit>
        {
            new QuantityPerUnit { QuantityPerUnitId = "1", Quantity = "10" },
            new QuantityPerUnit { QuantityPerUnitId = "2", Quantity = "20" },
            new QuantityPerUnit { QuantityPerUnitId = "3", Quantity = "25" },
            new QuantityPerUnit { QuantityPerUnitId = "4", Quantity = "50" },
            new QuantityPerUnit { QuantityPerUnitId = "5", Quantity = "100" }
        };
    }
}


[HttpGet]
public ActionResult ProductEdit(Int32 ProductId)
{
    var northwind = new NorthwindEntities();

    var q = from p in northwind.Products
            where p.ProductID == ProductId
            select new ProductEditViewModel
            {
                ProductID = p.ProductID,
                ProductName = p.ProductName,
                UnitPrice = p.UnitPrice,
                Discontinued = p.Discontinued,

                SupplierItems = from sup in northwind.Suppliers
                                select new SelectListItem
                                    {
                                        Text = sup.CompanyName,
                                        Value = SqlFunctions.StringConvert((double)sup.SupplierID),
                                        Selected = sup.SupplierID == p.SupplierID
                                    },

                CategorySelectedId = p.CategoryID,
                CategorieItems = from cat in northwind.Categories select cat,

                QuantityPerUnitSelectedId = p.QuantityPerUnit,
                QuantityPerUnitItems = QuantityPerUnit.QuantityPerUnitItems
            };

    return View(q.SingleOrDefault());
}


<div class="form-group">
    @Html.LabelFor(model => model.QuantityPerUnit)
    @foreach(var Quantity in MvcApplication1.Models.QuantityPerUnit.QuantityPerUnitItems)
    {
        @Html.CheckBoxFor(model => model.QuantityPerUnitSelectedId == Quantity.QuantityPerUnitId, Quantity.QuantityPerUnitId)
    }
</div>

Answer 1

您需要将要转换为SQL的部分分离出来，并由数据库从您希望在应用程序端完成的部分执行。

var q = (from p in northwind.Products
        where p.ProductID == ProductId
        select new ProductEditViewModel
        {
            ProductID = p.ProductID,
            ProductName = p.ProductName,
            UnitPrice = p.UnitPrice,
            Discontinued = p.Discontinued,

            SupplierItems = from sup in northwind.Suppliers
                            select new SelectListItem
                                {
                                    Text = sup.CompanyName,
                                    Value = SqlFunctions.StringConvert((double)sup.SupplierID),
                                    Selected = sup.SupplierID == p.SupplierID
                                },

            CategorySelectedId = p.CategoryID,
            CategorieItems = from cat in northwind.Categories select cat,

            QuantityPerUnitSelectedId = p.QuantityPerUnit,
            //remove this from here
            //QuantityPerUnitItems = QuantityPerUnit.QuantityPerUnitItems
        })
        .AsEnumerable()
        .Select(p => new ProductEditViewModel
        {
            p.ProductID,
            //all of the other properties 
            QuantityPerUnitItems = QuantityPerUnit.QuantityPerUnitItems,
        };

Answer 2

马修。

从数据库获取项目时，使用IQueryable（T）类型进行操作。此类型转换为SQL脚本。这种LINQ被称为 - Linq to entities。

要执行操作，您需要使用Linq to Objects。

您需要在方法AsEnumerable（）的帮助下将查询转换为IEnumerable（T），然后将静态数据添加到ViewModel。

当linq查询具有List对象时，Entity Framework无法生成表达式树

2 个答案: