Question

我需要从my-sql server数据库中检索员工，具体取决于传递的id参数。例如：http://localhost:66666/employee/details/1 <---the parameter 并将参数与数据库中的id匹配，并在视图中显示。出于某种原因，我在员工控制器中的此行上收到了无效的操作异常：Employee employee = EmployeeContext.Employees.Single(emp => emp.EmployeeID == id);

我不确定错误是否真的来自那里。

员工控制员

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

namespace MVCTutorials.Controllers
{
    public class EmployeeController : Controller
    {
        // GET: Employee
        public ActionResult Details(int id)//id =paramenter 
        {

            EmployeeContext EmployeeContext = new EmployeeContext();

            Employee employee = EmployeeContext.Employees.Single(emp => emp.EmployeeID == id);
            return View(employee);

        }
    }
}

员工模式

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

namespace MVCTutorials.Models
{
    [Table("TblEmp")]
    public class Employee
    {
        [Key]
        public int EmployeeID { get; set; }
        public string Name { get; set; }
        public string Gender { get; set; }
        public string City { get; set; }
    }
}

员工观点

@model MVCTutorials.Models.Employee
@{
    ViewBag.Title = "Employeee Details";
}

<h2>Employeee Details</h2>

<table style="font-family:Arial;">
    <tr><!--The Row-->
        <td>
                <b>Employee Id: </b>
        </td>
        <td>
            @Model.EmployeeID
        </td> 
    </tr>
    <tr>
        <td>
            Name:
        </td>
        <td>
            @Model.Name
        </td>
    </tr>
    <tr>
        <td>Gender:</td>
        <td>@Model.Gender</td>
    </tr>
    <tr>
        <td>City:</td>
        <td>@Model.City </td>
    </tr>
</table>

员工背景

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

namespace MVCTutorials.Models
{
    public  class EmployeeContext : DbContext
    {
        public DbSet<Employee> Employees { get; set; }
    }
}

Global.aspx

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.Optimization;
using System.Web.Routing;

namespace MVCTutorials
{
    public class MvcApplication : System.Web.HttpApplication
    {
        //Happens when appplication first starts
        protected void Application_Start()
        {
            //Purpose used to initalize your database e.g if you dont have a database created already this will create one for you(database,tables and data will all be created)
            // we pass null saying we dont want any of this
            Database.SetInitializer<MVCTutorials.Models.EmployeeContext>(null);
            AreaRegistration.RegisterAllAreas();
            GlobalConfiguration.Configure(WebApiConfig.Register);
            FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
            RouteConfig.RegisterRoutes(RouteTable.Routes);
            BundleConfig.RegisterBundles(BundleTable.Bundles);
        }
    }
}

Answer 1

Single方法返回序列的唯一元素，如果序列中没有一个元素，则抛出异常。所以你可以使用SingleOrDefault函数，如果你有任何想要的行，它返回null。

Employee employee = EmployeeContext.Employees.SingleOrDefault(emp => emp.EmployeeID == id);

Answer 2

根据MSDN for Enumerable.Single()：

出现InvalidOperationException 输入序列包含多个元素。 -要么- 输入序列为空。

我相信您有多个符合条件的员工或没有符合条件的员工，因此会抛出异常。

如果可能存在多个First()，则应使用Employee或使用SingleOrDefault并检查null。

Answer 3

不使用Single方法，而是使用Find，然后验证是否找到了它。

Employee employee = EmployeeContext.Employees.Find(id);
if (employee == null)
    // not found on database

作为per documentation，Single方法只有在符合条件的情况下才会成功。不少于一条记录。

Mvc无效的操作异常

3 个答案: