linq中怎么解决这个问题:Cannot add an entity with a key that is already in use.

Question

错误信息：Cannot add an entity with a key that is already in use.
错误源：App_Web_vvfzwtzj
堆栈跟踪： 在 UserManagerUC.imgBtnSubmit_Click(Object sender, ImageClickEventArgs e) 位置 d:\MyWork\IM\Controls\UserManagerUC.ascx.cs:行号 361

C# code

  protected void imgBtnSubmit_Click(object sender, ImageClickEventArgs e)

        {

            this.DoInit();

            try

            {

                DBIMDataContext IM = (DBIMDataContext)Application["IM"];

               

                try

                {

                    var users = from user in IM.Users

                                where user.userID == this.txtUserID.Text

                                select user;

 

                    if (users.Count<User>()>0)

                    {

                        this.lblFailed.Text = "This user has been existed!";

                        this.lblFailed.Visible = true;

                        return;

                    }

                    if (string.IsNullOrEmpty(this.txtAddress.Text))

                    {

                        this.lblFailed.Visible = true;

                        this.lblFailed.Text = "Address is empty!";

                    }

                    else if (string.IsNullOrEmpty(this.txtCompany.Text))

                    {

                        this.lblFailed.Visible = true;

                        this.lblFailed.Text = "Company is empty!";

                    }

                    else if (string.IsNullOrEmpty(this.txtEmail.Text))

                    {

                        this.lblFailed.Visible = true;

                        this.lblFailed.Text = "Email is empty!";

                    }

                    else if (string.IsNullOrEmpty(this.txtPassword.Text))

                    {

                        this.lblFailed.Visible = true;

                        this.lblFailed.Text = "Password is empty!";

                    }

                    else if (string.IsNullOrEmpty(this.txtTelphone.Text))

                    {

                        this.lblFailed.Visible = true;

                        this.lblFailed.Text = "Telphone is empty!";

                    }

                    else

                    {

                        User xUser = new User();

                        xUser.userID = this.txtUserID.Text;

                        xUser.address = this.txtAddress.Text;

                        xUser.company = this.txtCompany.Text;

                        xUser.email = this.txtEmail.Text;

                        if (string.IsNullOrEmpty(this.txtNickName.Text))

                        {

                            xUser.nickName = this.txtUserID.Text;

                        }

                        else

                        {

                            xUser.nickName = this.txtNickName.Text;

                        }

                        xUser.orderFlag = int.Parse(this.ddlOrderFlag.SelectedValue);

                        xUser.password = this.txtPassword.Text;

                        xUser.roleID = this.rblRoles.SelectedValue;

                        xUser.telphone = this.txtTelphone.Text;

                       

                        IM.Users.InsertOnSubmit(xUser);

                        IM.SubmitChanges();

 

                        this.divList.Visible = true;

                        this.BindGVUsers();

                    }

                }

                catch (Exception exception)

                {

                    throw exception;

                }

            }

            catch (Exception exception)

            {

                try

                {

                    //发送错误信息给管理员

                    MyMail mail = new MyMail();

                    mail.Send(exception);

 

                    this.lblFailed.Visible = true;

                    this.lblFailed.Text = exception.Message;

                }

                catch (Exception ex)

                {

                    this.lblFailed.Visible = true;

                    this.lblFailed.Text = ex.Message;

                }

            }

          

        }

Answer 1

终于解决了...

Answer 2

一：若数据库做了更改之后，在设计器中实体必须做一下修正。（这是罪魁祸首） 二：检查一下数据库，与你将要变更的数据，在唯一性的字段上是否有重复项。 三：检查一下Key的设置，一般都是有符号自增。（这样设置是绝对不会出现此错误，无符号自增在批量插入时有可能会出错） 在DataContext未提交时候，数据都在内存中的，当提交时候，内存中的Key与服务器的Key会做对比，若是自增列，服务器会有一个ID，会自动给内存中的Key赋值并自增。若不是自增列，则会判断服务器上的Key是否已存在，若存在则会报Key已使用的异常。 Linq中有AttachAll这个方法，这是更新一组数据的，此方法会把内存中的Key到服务器查找，若内存中Key存在重复也会报错误，因为批量时候内存中的Key会按顺序的一个一个被使用，而且事物未完成是不释放，所以当内存中Key存在重复了，就无法进行下去。若这方法更新一条记录则无此问题。 若更新的一组记录中只要有一个Key查找不到，则看是否把asModify这个参数设为true，若设为true则提交时候直接抛出异常，事物断开，之前更新的不会滚。若设为false则不报异常，事物回滚，一组数据无一更新。