System.Data.Entity.Infrastructure.DbUpdateConcurrencyException

Question

我得到了这个错误：

异常在这里的db.SaveChanges()行中发生；db.SaveChanges发生在EntityFramework.dll.Store update、insert或delete语句中，影响到意外的行数(0)。实体可能已被修改或删除，因为实体是加载的。

密码有什么问题吗？请帮帮我。下面是我的密码。

模型类：

public class EmployeeDb : DbContext
{
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {        base.OnModelCreating(modelBuilder);
        modelBuilder.Entity<Employee>().ToTable("EmployeeTable");
    }
    public DbSet<Employee> Employees { get; set; }
}

public class Employee
{
    [Key]
    public int EmployeeID { get; set; }
    public string EmployeeName { get; set; }
    public string EmployeeAddress { get; set; }
    public string EmployeeEmail { get; set; }
}

控制器类：

public class EmployeeController : Controller
{
    public ActionResult Index()
    {
        return View();
    }

    [HttpPost]
    public ActionResult Create(Employee emp)
    {
        EmployeeDb dbobj = new EmployeeDb();
        dbobj.Employees.Add(emp);
        dbobj.SaveChanges();
        return View("Employee",emp);
    }
}

意见：

@model EmployeeMgmt.Models.Employee

@using (Html.BeginForm("Create","Employee",FormMethod.Post)) 
{
    @Html.AntiForgeryToken()   

<div class="form-horizontal">
    <h4>Employee</h4>
    <hr />
    @Html.ValidationSummary(true, "", new { @class = "text-danger" })
    <div class="form-group">
        @Html.LabelFor(model => model.EmployeeID, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.EmployeeID, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.EmployeeID, "", new { @class = "text-danger" })
        </div>
    </div>
    <div class="form-group">
        @Html.LabelFor(model => model.EmployeeName, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.EmployeeName, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.EmployeeName, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.EmployeeAddress, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.EmployeeAddress, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.EmployeeAddress, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.EmployeeEmail, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.EmployeeEmail, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.EmployeeEmail, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        <div class="col-md-offset-2 col-md-10">
            <input type="submit" value="Create" class="btn btn-default" />
        </div>
    </div>
</div>
}

<div>
    @Html.ActionLink("Back to List", "Index")
</div>

是什么导致了这个错误，以及如何修复它？

Answer 1

@Sushma您的Id字段必须包含唯一的编号。这通常是通过允许数据库为您选择该号码来完成的。在某些情况下，它可以由代码生成，但这在多用户系统中是很困难的。最简单的修复方法是将[DatabaseGenerated(DatabaseGeneratedOption.Identity)]添加到模型中的id字段。您还需要创建一个迁移来用这个新设置更新数据库。

public class Employee
{
  [Key]
  [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
  public int EmployeeID { get; set; }
  public string EmployeeName { get; set; }
  public string EmployeeAddress { get; set; }
  public string EmployeeEmail { get; set; }
}