public static int ExecuteNonQuery(out int id, DbConnection connection, CommandType commandType, string commandText, params DbParameter[] commandParameters)
        {
            if (connection == null) throw new ArgumentNullException("connection");
            if (string.IsNullOrEmpty(Provider.GetLastIdSql().Trim())) throw new ArgumentNullException(" GetLastIdSql is  Null Or Empty" );

            // 创建DbCommand命令,并进行预处理
            DbCommand cmd = Factory.CreateCommand();
            bool mustCloseConnection = false;
            PrepareCommand(cmd, connection, (DbTransaction)null, commandType, commandText, commandParameters, out mustCloseConnection);

            // 执行命令
            int retval = cmd.ExecuteNonQuery();//这里没问题
            // 清除参数,以便再次使用.
            cmd.Parameters.Clear();
            cmd.CommandType = CommandType.Text;
            cmd.CommandText = Provider.GetLastIdSql();

            System.Diagnostics.Debug.Assert(cmd.ExecuteScalar()==null);//总是返回空
            id = int.Parse(cmd.ExecuteScalar().ToString());

            m_querycount++;


            if (mustCloseConnection)
            {
                connection.Close();
            }
            return retval;
        }

我运行一个insert语句，前面的运行良好，可是后面的取回自增值就报错了，返回的总是空值。郁闷来了。自己在外面写的时候好好的，放到这里面就不行了。

其它内部方法

        private static void PrepareCommand(DbCommand command, DbConnection connection, DbTransaction transaction, CommandType commandType, string commandText, DbParameter[] commandParameters, out bool mustCloseConnection)
        {
            if (command == null) throw new ArgumentNullException("command");
           if (string.IsNullOrEmpty(commandText)) throw new ArgumentNullException("commandText");

            // If the provided connection is not open, we will open it
            if (connection.State != ConnectionState.Open)
            {
                mustCloseConnection = true;
                connection.Open();
            }
            else
            {
                mustCloseConnection = false;
            }

            // 给命令分配一个数据库连接.
            command.Connection = connection;

            // 设置命令文本(存储过程名或SQL语句)
            command.CommandText = commandText;

            // 分配事务
            if (transaction != null)
            {
                if (transaction.Connection == null) throw new ArgumentException("The transaction was rollbacked or commited, please provide an open transaction.", "transaction");
                command.Transaction = transaction;
            }

            // 设置命令类型.
            command.CommandType = commandType;

            // 分配命令参数
            if (commandParameters != null)
            {
                AttachParameters(command, commandParameters);
            }
            return;
        }

        public string GetLastIdSql()
        {
            return "SELECT SCOPE_IDENTITY()";
        }

---

　　　　//System.Data.SqlClient.SqlCommand cmd = new System.Data.SqlClient.SqlCommand("insert into lcs_Sys_Model ([Model_GUID],[Model_Name],[Model_Desp],[Model_IsSys]) values ( 'F3CD1369-58C0-4A1F-AF88-05FCF734E079','name','desp',1 )", new System.Data.SqlClient.SqlConnection(@"Integrated Security=SSPI;Persist Security Info=False;Initial Catalog=officially;Data Source=LCSNB\SQL2K"));
            //cmd.Connection.Open();
            //cmd.ExecuteNonQuery();
            //cmd.Parameters.Clear();
            //cmd.CommandText = "SELECT SCOPE_IDENTITY()";
            //Console.WriteLine(cmd.ExecuteScalar().ToString());
            //cmd.Connection.Close();

这个没问题，他们有啥区别呢？看不出个所以然来。