MVC新手无法从数据库中获取数据

时间：2014-08-09 02:57:59

标签： asp.net-mvc database model-view-controller

我对MVC完全不熟悉。我遵循一个教程，您应该连接到数据库并从表中提取数据。不幸的是，这不起作用。我应该能够在“localhost：12345”之后的地址栏中添加“/ Employee / Details / 1”并获取位于表格第一行的值。我不确定要发布什么代码，所以我会发布我认为相关的内容以及错误详细信息的副本。如果我需要发布更多代码以获得更多帮助，请告诉我。谢谢！

EmployeeController.cs 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using MvcDemo2.Models;

namespace MvcDemo2.Controllers
{
    public class EmployeeController : Controller
    {
        //
        // GET: /Employee/

        public ActionResult Details(int id)
        {
            EmployeeContext employeeContext = new EmployeeContext();
            Employee employee = employeeContext.Employees.Single(emp => emp.EmployeeId == id);  //THIS IS THE LINE HIGHLIGHTED AS PART OF THE ERROR
            return View(employee);
        }

    }
}

＆lt; -------下一个文件--------＆gt; 

Employee.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.ComponentModel.DataAnnotations.Schema;
using System.ComponentModel.DataAnnotations;

namespace MvcDemo2.Models
{

     [Table("dbo.Employees")]
    public class Employee
    {
        [Key]
        public int EmployeeId { get; set; }
        public string Name { get; set; }
        public string Gender { get; set; }
        public string City { get; set; }



    }
}

＆lt; -------下一个文件--------＆gt;

EmployeeContext.cs 

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


namespace MvcDemo2.Models
{


    public class EmployeeContext : DbContext
    {
        public DbSet<Employee> Employees { get; set; }
    }
}

＆lt; -------下一个文件--------＆gt;

的Web.config 

<?xml version="1.0" encoding="utf-8"?>
<!--
  For more information on how to configure your ASP.NET application, please visit
  http://go.microsoft.com/fwlink/?LinkId=169433
  -->
<configuration>
  <configSections>
    <!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 -->
    <section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
  </configSections>
  <appSettings>
    <add key="webpages:Version" value="2.0.0.0" />
    <add key="webpages:Enabled" value="false" />
    <add key="PreserveLoginUrl" value="true" />
    <add key="ClientValidationEnabled" value="true" />
    <add key="UnobtrusiveJavaScriptEnabled" value="true" />
  </appSettings>
  <system.web>
    <compilation debug="true" targetFramework="4.0" />
    <pages>
      <namespaces>
        <add namespace="System.Web.Helpers" />
        <add namespace="System.Web.Mvc" />
        <add namespace="System.Web.Mvc.Ajax" />
        <add namespace="System.Web.Mvc.Html" />
        <add namespace="System.Web.Routing" />
        <add namespace="System.Web.WebPages" />
      </namespaces>
    </pages>
  </system.web>
  <system.webServer>
    <validation validateIntegratedModeConfiguration="false" />
    <modules runAllManagedModulesForAllRequests="true" />
    <handlers>
      <remove name="ExtensionlessUrlHandler-ISAPI-4.0_32bit" />
      <remove name="ExtensionlessUrlHandler-ISAPI-4.0_64bit" />
      <remove name="ExtensionlessUrlHandler-Integrated-4.0" />
      <add name="ExtensionlessUrlHandler-ISAPI-4.0_32bit" path="*." verb="GET,HEAD,POST,DEBUG,PUT,DELETE,PATCH,OPTIONS" modules="IsapiModule" scriptProcessor="%windir%\Microsoft.NET\Framework\v4.0.30319\aspnet_isapi.dll" preCondition="classicMode,runtimeVersionv4.0,bitness32" responseBufferLimit="0" />
      <add name="ExtensionlessUrlHandler-ISAPI-4.0_64bit" path="*." verb="GET,HEAD,POST,DEBUG,PUT,DELETE,PATCH,OPTIONS" modules="IsapiModule" scriptProcessor="%windir%\Microsoft.NET\Framework64\v4.0.30319\aspnet_isapi.dll" preCondition="classicMode,runtimeVersionv4.0,bitness64" responseBufferLimit="0" />
      <add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="GET,HEAD,POST,DEBUG,PUT,DELETE,PATCH,OPTIONS" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" />
    </handlers>
  </system.webServer>
  <entityFramework>
    <defaultConnectionFactory type="System.Data.Entity.Infrastructure.LocalDbConnectionFactory, EntityFramework">
      <parameters>
        <parameter value="v11.0" />
      </parameters>
    </defaultConnectionFactory>
    <providers>
      <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
    </providers>
  </entityFramework>
  <connectionStrings>
    <add name="EmployeeContext"
         connectionString="server=MISSIONCNTRL-PC\SQLEXPRESS; database=Sample; integrated security=SSPI"
         providerName="System.Data.SqlClient"/>
  </connectionStrings>
</configuration>

＆lt; -------下一个文件--------＆gt;

的Global.asax.cs 

using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;
using System.Web;
using System.Web.Http;
using System.Web.Mvc;
using System.Web.Routing;

namespace MvcDemo2
{
    // Note: For instructions on enabling IIS6 or IIS7 classic mode,
    // visit http://go.microsoft.com/?LinkId=9394801
    public class MvcApplication : System.Web.HttpApplication
    {
        protected void Application_Start()
        {
            Database.SetInitializer<MvcDemo2.Models.EmployeeContext>(null);
            AreaRegistration.RegisterAllAreas();

            WebApiConfig.Register(GlobalConfiguration.Configuration);
            FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
            RouteConfig.RegisterRoutes(RouteTable.Routes);
        }
    }
}

＆lt; -----错误信息-----＆gt; 

System.InvalidOperationException was unhandled by user code
  HResult=-2146233079
  Message=Sequence contains no elements
  Source=System.Core
  StackTrace:
       at System.Linq.Enumerable.Single[TSource](IEnumerable`1 source)
       at System.Data.Entity.Core.Objects.ELinq.ObjectQueryProvider.<GetElementFunction>b__3[TResult](IEnumerable`1 sequence)
       at System.Data.Entity.Core.Objects.ELinq.ObjectQueryProvider.ExecuteSingle[TResult](IEnumerable`1 query, Expression queryRoot)
       at System.Data.Entity.Core.Objects.ELinq.ObjectQueryProvider.System.Linq.IQueryProvider.Execute[TResult](Expression expression)
       at System.Data.Entity.Internal.Linq.DbQueryProvider.Execute[TResult](Expression expression)
       at System.Linq.Queryable.Single[TSource](IQueryable`1 source, Expression`1 predicate)
       at MvcDemo2.Controllers.EmployeeController.Details(Int32 id) in d:\Visual Studio 2012\Projects\MvcDemo2\MvcDemo2\Controllers\EmployeeController.cs:line 18
       at lambda_method(Closure , ControllerBase , Object[] )
       at System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters)
       at System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters)
       at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters)
       at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass42.<BeginInvokeSynchronousActionMethod>b__41()
       at System.Web.Mvc.Async.AsyncResultWrapper.<>c__DisplayClass8`1.<BeginSynchronous>b__7(IAsyncResult _)
       at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`1.End()
       at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod(IAsyncResult asyncResult)
       at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass37.<>c__DisplayClass39.<BeginInvokeActionMethodWithFilters>b__33()
       at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass4f.<InvokeActionMethodFilterAsynchronously>b__49()

FYI。我已经阅读了使用相同教程的其他线程，并尝试了他们的代码，但我仍然没有运气。真的可以在这个上使用一些帮助。试图解决这个问题对我很重要。

2 个答案:

答案 0 :(得分：0)

试试这个

public ActionResult Details(int id)
{
    EmployeeContext employeeContext = new EmployeeContext();
    Employee employee = employeeContext.Employees.Find(id);
    if (employee != null) 
      return View(employee);

    return new HttpStatusCodeResult(HttpStatusCode.NotFound);
}

答案 1 :(得分：0)

@model MvcDemo2.Models.Employee

@{
    ViewBag.Title = "Details";
}

<h2>Employee Details</h2>
<table style="font-family: Arial">
    <tr>
        <td>
            <b>Employee Id:</b>
        </td>
        <td>
            @Model.EmployeeId //this is where the error is 
        </td>
    </tr>
    <tr>
        <td>
            <b>Name:</b>
        </td>
        <td>
            @Model.Name
        </td>
    </tr>
    <tr>
        <td>
            <b>Gender:</b>
        </td>
        <td>
            @Model.Gender
        </td>
    </tr>
    <tr>
        <td>
            <b>City:</b>
        </td>
        <td>
            @Model.City
        </td>
    </tr>
</table>

＆lt; -------- ERROR消息--------＆gt; 

System.NullReferenceException was unhandled by user code
  HResult=-2147467261
  Message=Object reference not set to an instance of an object.
  Source=App_Web_qs2w0l3a
  StackTrace:
       at ASP._Page_Views_Employee_Details_cshtml.Execute() in d:\Visual Studio 2012\Projects\MvcDemo2\MvcDemo2\Views\Employee\Details.cshtml:line 14
       at System.Web.WebPages.WebPageBase.ExecutePageHierarchy()
       at System.Web.Mvc.WebViewPage.ExecutePageHierarchy()
       at System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage)
       at System.Web.Mvc.RazorView.RenderView(ViewContext viewContext, TextWriter writer, Object instance)
       at System.Web.Mvc.BuildManagerCompiledView.Render(ViewContext viewContext, TextWriter writer)
       at System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context)
       at System.Web.Mvc.ControllerActionInvoker.InvokeActionResult(ControllerContext controllerContext, ActionResult actionResult)
       at System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClass1a.<InvokeActionResultWithFilters>b__17()
       at System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilter(IResultFilter filter, ResultExecutingContext preContext, Func`1 continuation)
  InnerException:

Thankyou dasu908的帮助。我真的很沮丧。

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