如何获取自增长列（标识列）的ID，并写入另一张表(多对多关系插入数据示例)

问题
CSDN 里面不时有初学者疑惑：如何获取自增长列（标识列）的ID，并写入另一张表。

场景
这里选择典型的多对多关系，并以常见的 User-Role 作为 Demo，同时显示 Access 和 Sql Server 版本

关系图


实现要点
1， 如何获取新插入记录生成的 ID：Sql Server 和 Access（当使用 Jet ADO，当然包括ADO.NET，连接时）均支持 @@Identity 全局变量，返回在当前会话的所有表中生成的最后一个标识值
2，同时写入多张表需要显示使用事务

MS Access 版本 

<% @ Page Language="C#"  %>
<% @ Import Namespace="System.Data"  %>
<% @ Import Namespace="System.Data.OleDb"  %>

<! DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" >

< script  runat ="server" >

    string connStr;

    protected void Page_Load(object sender, EventArgs e)
    {
        connStr = "provider=Microsoft.Jet.OleDb.4.0;data source=" + Server.MapPath("~/App_Data/DemoManyToMany.mdb");
    }
    
    protected void btnLogin_Click(object sender, EventArgs e)
    {
        if (chkRoles.SelectedIndex == -1) throw new Exception("至少选择一个角色。");        
        
        string sqlInserUser = "INSERT INTO [User]([UserName], [Password]) VALUES(?, ?)";
        string sqlInserUserRoel = "INSERT INTO UserRole([UserId], [RoleId]) VALUES(?, ?)";
        string sqlSelectNewUserId = "SELECT @@Identity"; // OR "SELECT MAX([UserId]) FROM [User]";
        using (OleDbConnection conn = new OleDbConnection(connStr)) {            
            conn.Open();
            // 显示开启事务
            OleDbTransaction trans = conn.BeginTransaction();            
            OleDbCommand cmd = conn.CreateCommand();
            // 关联事务
            cmd.Transaction = trans;           
            
            try {
                cmd.CommandText = sqlInserUser;
                cmd.Parameters.Add("UserName", txtUserName.Text);
                cmd.Parameters.Add("Password", txtPassword.Text);
                // 插入 User
                cmd.ExecuteNonQuery();                               

                cmd.CommandText = sqlSelectNewUserId;
                // 读取新插入 UserId
                int newUserId = (int)cmd.ExecuteScalar();

                // 仅供测试
                if (chkGeneratError.Checked) throw new Exception("创建用户时发生错误。");

                cmd.CommandText = sqlInserUserRoel;
                cmd.Parameters.Clear();
                cmd.Parameters.Add("UserId", OleDbType.Integer);
                cmd.Parameters.Add("RoleId", OleDbType.Integer);
                cmd.Parameters[0].Value = newUserId;
                // 遍历可选角色列表
                foreach (ListItem item in chkRoles.Items) {
                    if (item.Selected) {
                        cmd.Parameters[1].Value = item.Value;
                        // 写入中间关系表 UserRole
                        cmd.ExecuteNonQuery();
                    }
                }
                // 提交事务
                trans.Commit();
                lblMsg.Text = String.Format("用户 '{0}' 创建成功。\n事务已提交。", txtUserName.Text);                             
            }
            catch(Exception inner) {
                // 发生错误，回滚事务
                if (trans != null) trans.Rollback();
                lblMsg.Text = String.Format("用户 '{0}' 创建失败。\n事务已回滚。\n详细信息：{1}", txtUserName.Text, inner.Message);
                //throw new Exception("创建用户失败。事务已回滚。", inner);
            }                        
        }
        // 重新加载 User 数据
        grdvUsers.DataBind();
    }

    protected void grdvUsers_RowDataBound(object sender, GridViewRowEventArgs e)
    {        
        // 加载每个 User 对应的 Roles
        DataList dlstRolesOfUser = e.Row.FindControl("dlstRolesOfUser") as DataList;
        if(dlstRolesOfUser == null) return;
        
        int userId = (int)grdvUsers.DataKeys[e.Row.RowIndex].Value;
        
        string sqlSelectRoleOfUser =
            "SELECT Role.RoleName FROM (Role INNER JOIN UserRole ON Role.RoleId = UserRole.RoleId) WHERE UserRole.UserId=?";
        OleDbDataAdapter da = new OleDbDataAdapter(sqlSelectRoleOfUser, connStr);
        da.SelectCommand.Parameters.Add("UserId", userId);
        DataTable dtRolesOfUser = new DataTable();
        da.Fill(dtRolesOfUser);
        dlstRolesOfUser.DataSource = dtRolesOfUser;
        dlstRolesOfUser.DataBind();        
    }
    
</ script >

< html  xmlns ="http://www.w3.org/1999/xhtml"   >
< head  runat ="server" >
     < title > 多对多写入实例——Access版本 </ title >
</ head >
< body >
     < form  id ="form1"  runat ="server" >
     < div >        
         < h1 > 多对多写入实例——Access版本 </ h1 >
         < h3 > 创建用户 </ h3 >
         < table  border ="1" >
             < tr >
                 < td >
                    用户名：
                 </ td >
                 < td >
                     < asp:TextBox  ID ="txtUserName"  runat ="server" ></ asp:TextBox >
                     < asp:RequiredFieldValidator  ID ="RequiredFieldValidator1"  runat ="server"  ControlToValidate ="txtUserName"
                        Display ="Dynamic"  ErrorMessage ="Required" ></ asp:RequiredFieldValidator ></ td >
             </ tr >
             < tr >
                 < td >
                    密码：
                 </ td >
                 < td >
                     < asp:TextBox  ID ="txtPassword"  runat ="server" ></ asp:TextBox ></ td >
             </ tr >
             < tr >
                 < td >
                    角色：
                 </ td >
                 < td >
                     < asp:CheckBoxList  ID ="chkRoles"  runat ="server"  DataSourceID ="AccessDataSource1"  DataTextField ="RoleName"  DataValueField ="RoleId"  RepeatDirection ="Horizontal" ></ asp:CheckBoxList >< asp:AccessDataSource  ID ="AccessDataSource1"  runat ="server"  DataFile ="~/App_Data/DemoManyToMany.mdb"
                        SelectCommand ="SELECT [RoleId], [RoleName] FROM [Role]" ></ asp:AccessDataSource >
                 </ td >
             </ tr >
             < tr >
                 < td >
                    强制发生错误：
                 </ td >
                 < td >
                     < asp:CheckBox  ID ="chkGeneratError"  runat ="server"   /></ td >
             </ tr >
             < tr >
                 < td >
                 </ td >
                 < td >
         < asp:Button  ID ="btnLogin"  runat ="server"  Text ="确定"  OnClick ="btnLogin_Click"   /></ td >
             </ tr >
         </ table >
         < pre >< asp:Label  ID ="lblMsg"  runat ="server"  ForeColor ="red" ></ asp:Label ></ pre >
         < br  />
     </ div >
     < h3 > 用户列表 </ h3 >
         < asp:GridView  ID ="grdvUsers"  runat ="server"  AutoGenerateColumns ="False"  DataKeyNames ="UserId"
            DataSourceID ="AccessDataSource2"  OnRowDataBound ="grdvUsers_RowDataBound" >
             < Columns >
                 < asp:BoundField  DataField ="UserId"  HeaderText ="UserId"  InsertVisible ="False"  ReadOnly ="True"
                    SortExpression ="UserId"   />
                 < asp:BoundField  DataField ="UserName"  HeaderText ="UserName"  SortExpression ="UserName"   />
                 < asp:BoundField  DataField ="Password"  HeaderText ="Password"  SortExpression ="Password"   />
                 < asp:TemplateField  HeaderText ="角色" >
                     < ItemTemplate >
                     < asp:Datalist  id ="dlstRolesOfUser"  runat ="server"  RepeatDirection ="Horizontal" >
                         < ItemTemplate > <% # Eval("RoleName")  %> </ ItemTemplate >
                         < AlternatingItemTemplate > , <% # Eval("RoleName")  %> </ AlternatingItemTemplate >
                     </ asp:datalist >
                     </ ItemTemplate >
                 </ asp:TemplateField >
             </ Columns >
             < EmptyDataTemplate >
                暂无数据
             </ EmptyDataTemplate >
         </ asp:GridView >
         < asp:AccessDataSource  ID ="AccessDataSource2"  runat ="server"  DataFile ="~/App_Data/DemoManyToMany.mdb"
            SelectCommand ="SELECT [UserId], [UserName], [Password] FROM [User]" ></ asp:AccessDataSource >
     </ form >
</ body >
</ html >

MS SQL Server 版本

<% @ Page Language="C#"  %>
<% @ Import Namespace="System.Data"  %>
<% @ Import Namespace="System.Data.SqlClient"  %>

<! DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" >

< script  runat ="server" >

    string connStr;

    protected void Page_Load(object sender, EventArgs e)
    {
        connStr = "server=.;database=DemoLib;uid=sa";
    }
    
    protected void btnLogin_Click(object sender, EventArgs e)
    {
        if (chkRoles.SelectedIndex == -1) throw new Exception("至少选择一个角色。");        
        
        string sqlInserUser = "INSERT INTO [User]([UserName], [Password]) VALUES(@UserName, @Password) SELECT @NewUserId=@@Identity";
        string sqlInserUserRoel = "INSERT INTO UserRole([UserId], [RoleId]) VALUES(@UserId, @RoleId)";
        string sqlSelectNewUserId = "SELECT @@Identity"; // OR "SELECT MAX([UserId]) FROM [User]";
        using (SqlConnection conn = new SqlConnection(connStr)) {            
            conn.Open();
            // 显示开启事务
            SqlTransaction trans = conn.BeginTransaction();            
            SqlCommand cmd = conn.CreateCommand();
            // 关联事务
            cmd.Transaction = trans;           
            
            try {
                cmd.CommandText = sqlInserUser;
                cmd.Parameters.Add("UserName", txtUserName.Text);
                cmd.Parameters.Add("Password", txtPassword.Text);
                // 此输出参数返回新插入 UserId
                cmd.Parameters.Add("NewUserId", SqlDbType.Int).Direction = ParameterDirection.Output;
                // 插入 User
                cmd.ExecuteNonQuery();                               

                /**//* 以下方法依然有效，只是我们选择更加简便方法：批处理SQL语句
                cmd.CommandText = sqlSelectNewUserId;
                // 读取新插入 UserId
                int newUserId = (int)cmd.ExecuteScalar();
                 */
                int newUserId = (int)cmd.Parameters["NewUserId"].Value;

                // 仅供测试
                if (chkGeneratError.Checked) throw new Exception("创建用户时发生错误。");

                cmd.CommandText = sqlInserUserRoel;
                cmd.Parameters.Clear();
                cmd.Parameters.Add("UserId", SqlDbType.Int);
                cmd.Parameters.Add("RoleId", SqlDbType.Int);
                cmd.Parameters[0].Value = newUserId;
                // 遍历可选角色列表
                foreach (ListItem item in chkRoles.Items) {
                    if (item.Selected) {
                        cmd.Parameters[1].Value = item.Value;
                        // 写入中间关系表 UserRole
                        cmd.ExecuteNonQuery();
                    }
                }
                // 提交事务
                trans.Commit();
                lblMsg.Text = String.Format("用户 '{0}' 创建成功。\n事务已提交。", txtUserName.Text);                             
            }
            catch(Exception inner) {
                // 发生错误，回滚事务
                if (trans != null) trans.Rollback();
                lblMsg.Text = String.Format("用户 '{0}' 创建失败。\n事务已回滚。\n详细信息：{1}", txtUserName.Text, inner.Message);
                //throw new Exception("创建用户失败。事务已回滚。", inner);
            }                        
        }
        // 重新加载 User 数据
        grdvUsers.DataBind();
    }

    protected void grdvUsers_RowDataBound(object sender, GridViewRowEventArgs e)
    {        
        // 加载每个 User 对应的 Roles
        DataList dlstRolesOfUser = e.Row.FindControl("dlstRolesOfUser") as DataList;
        if(dlstRolesOfUser == null) return;
        
        int userId = (int)grdvUsers.DataKeys[e.Row.RowIndex].Value;
        
        string sqlSelectRoleOfUser =
            "SELECT Role.RoleName FROM (Role INNER JOIN UserRole ON Role.RoleId = UserRole.RoleId) WHERE UserRole.UserId=@UserId";
        SqlDataAdapter da = new SqlDataAdapter(sqlSelectRoleOfUser, connStr);
        da.SelectCommand.Parameters.Add("UserId", userId);
        DataTable dtRolesOfUser = new DataTable();
        da.Fill(dtRolesOfUser);
        dlstRolesOfUser.DataSource = dtRolesOfUser;
        dlstRolesOfUser.DataBind();        
    }
    
</ script >

< html  xmlns ="http://www.w3.org/1999/xhtml"   >
< head  runat ="server" >
     < title > 多对多写入实例——SqlServer版本 </ title >
</ head >
< body >
     < form  id ="form1"  runat ="server" >
     < div >        
         < h1 > 多对多写入实例——SqlServer版本 </ h1 >
         < h3 > 创建用户 </ h3 >
         < table  border ="1" >
             < tr >
                 < td >
                    用户名：
                 </ td >
                 < td >
                     < asp:TextBox  ID ="txtUserName"  runat ="server" ></ asp:TextBox >
                     < asp:RequiredFieldValidator  ID ="RequiredFieldValidator1"  runat ="server"  ControlToValidate ="txtUserName"
                        Display ="Dynamic"  ErrorMessage ="Required" ></ asp:RequiredFieldValidator ></ td >
             </ tr >
             < tr >
                 < td >
                    密码：
                 </ td >
                 < td >
                     < asp:TextBox  ID ="txtPassword"  runat ="server" ></ asp:TextBox ></ td >
             </ tr >
             < tr >
                 < td >
                    角色：
                 </ td >
                 < td >
                     < asp:CheckBoxList  ID ="chkRoles"  runat ="server"  DataSourceID ="SqlDataSource1"  DataTextField ="RoleName"  DataValueField ="RoleId"  RepeatDirection ="Horizontal" ></ asp:CheckBoxList >< asp:SqlDataSource  ID ="SqlDataSource1"  runat ="server"  ConnectionString ="Data Source=.;Initial Catalog=DemoLib;Integrated Security=True"
                        ProviderName ="System.Data.SqlClient"  SelectCommand ="SELECT [RoleId], [RoleName] FROM [Role]" >
                     </ asp:SqlDataSource >
                 </ td >
             </ tr >
             < tr >
                 < td >
                    强制发生错误：
                 </ td >
                 < td >
                     < asp:CheckBox  ID ="chkGeneratError"  runat ="server"   /></ td >
             </ tr >
             < tr >
                 < td >
                 </ td >
                 < td >
         < asp:Button  ID ="btnLogin"  runat ="server"  Text ="确定"  OnClick ="btnLogin_Click"   /></ td >
             </ tr >
         </ table >
         < pre >< asp:Label  ID ="lblMsg"  runat ="server"  ForeColor ="red" ></ asp:Label ></ pre >
         < br  />
     </ div >
     < h3 > 用户列表 </ h3 >
         < asp:GridView  ID ="grdvUsers"  runat ="server"  AutoGenerateColumns ="False"  DataKeyNames ="UserId"
            DataSourceID ="SqlDataSource2"  OnRowDataBound ="grdvUsers_RowDataBound" >
             < Columns >
                 < asp:BoundField  DataField ="UserId"  HeaderText ="UserId"  InsertVisible ="False"  ReadOnly ="True"
                    SortExpression ="UserId"   />
                 < asp:BoundField  DataField ="UserName"  HeaderText ="UserName"  SortExpression ="UserName"   />
                 < asp:BoundField  DataField ="Password"  HeaderText ="Password"  SortExpression ="Password"   />
                 < asp:TemplateField  HeaderText ="角色" >
                     < ItemTemplate >
                     < asp:Datalist  id ="dlstRolesOfUser"  runat ="server"  RepeatDirection ="Horizontal" >
                         < ItemTemplate > <% # Eval("RoleName")  %> </ ItemTemplate >
                         < AlternatingItemTemplate > , <% # Eval("RoleName")  %> </ AlternatingItemTemplate >
                     </ asp:datalist >
                     </ ItemTemplate >
                 </ asp:TemplateField >
             </ Columns >
             < EmptyDataTemplate >
                暂无数据
             </ EmptyDataTemplate >
         </ asp:GridView >
         < asp:SqlDataSource  ID ="SqlDataSource2"  runat ="server"  ConnectionString ="Data Source=.;Initial Catalog=DemoLib;Integrated Security=True"
            ProviderName ="System.Data.SqlClient"  SelectCommand ="SELECT [UserId], [UserName], [Password] FROM [User]" >
         </ asp:SqlDataSource >
         &nbsp;
     </ form >
</ body >
</ html >

下载： /Files/Jinglecat/DemoManyToMany_Insert.rar

update 2007年7月30日
这里 zjp1978 (铁血柔情) 提到 Access 中使用 @@Identity 无法获取正确值，主要原因是，没有使用显示事务，详细讨论见： http://community.csdn.net/Expert/TopicView3.asp?id=5661149