Question

我在MVC4中创建了一个新项目。我收到此错误： System.ArgumentNullException: Value can not be null. Parameter name: source. 数据库存在，表存在并填充数据。

任何提示？

Controler ShopController.cs

...  
    SQLEntities DB = new SQLEntities();  

    public ActionResult Index()
    {
        var x = DB.Types.ToList();          <-Here I get an exception
        return View(x);
    }
...

模型 Type.cs

using System.Collections.Generic;

namespace xxx.Models
{
    public class Type
    {
        public int TypeId { get; set; }
        public string Name { get; set; }
        public string Description { get; set; }
    }
}

模型 SQLEntities.cs

using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;
using System.Web;

namespace xxx.Models
{
    public class SQLEntities
    {
        public DbSet<Type> Types { get; set; }
    }
}

的Web.config

  <connectionStrings>
    <add name="SQLEntities" connectionString="Data Source=KOMPUTER\SQLEXPRESS;Initial Catalog=myDB;Integrated Security=True;" providerName="System.Data.SqlClient" />
  </connectionStrings>

编译器不指示任何错误。只有当他想要mypage/Shop获得例外时才会这样。

堆栈跟踪

{System.ArgumentNullException: Value can not be null.
Parameter name: source.
       w System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
       w Print.Controllers.StoreController.Index() w c:\Users\John\Documents\Visual Studio 2013\Projects\Print\Print\Controllers\StoreController.cs:wiersz 18
       w lambda_method(Closure , ControllerBase , Object[] )
       w System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters)
       w System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters)
       w System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters)
       w System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass42.<BeginInvokeSynchronousActionMethod>b__41()
       w System.Web.Mvc.Async.AsyncResultWrapper.<>c__DisplayClass8`1.<BeginSynchronous>b__7(IAsyncResult _)
       w System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`1.End()
       w System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod(IAsyncResult asyncResult)
       w System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass37.<>c__DisplayClass39.<BeginInvokeActionMethodWithFilters>b__33()
       w System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass4f.<InvokeActionMethodFilterAsynchronously>b__49()}

Answer 1

您的问题是SQLEntities应该继承自DbContext。

您的问题是SQLEntities.Types显然为空。您不应该被要求初始化此属性，因为当所有内容都正确设置时，EntityFramework会自动执行此属性。

将您的代码更改为：

   public class SQLEntities: DbContext
   {
       public DbSet<Type> Types { get; set; }
   }

MVC4 - 值不能为空。参数名称：source

1 个答案: