c#事务问题

Question

最近在学事务，发现一般更新删除的都没问题，但涉及select的就有些问题。

比如有这样一个场景，A需要用信用卡购买商品，购买之前需要先判断是否有足够的余额去购买。

我的代码是

    using (SqlConnection conn = new SqlConnection(”连接字符串))
            {
                conn.Open();
                using (SqlTransaction tran = conn.BeginTransaction())
                {
                    try
                    {
                        string strsql = "select balance from table where userid=1234"
                        decimal p1 = Execute(strsql,tran)  //取出余额    
                        decimal  p2=1.2 ; //需要付的款
                      //判断余额，足够购买，更新
                       if(p1>p2){
                       strsql = "update table set balance="+(p1--p2).ToString() +" where userid=1234";
                        ExecuteNonQuery(tran, strsql, null);
                        tran.Commit();
                       }
                    }
                    catch(Exception ex)
                    {
                        tran.Rollback();
                        Response.Write(ex.ToString());
                    }
                }
            }

 

但会出现错误，System.InvalidOperationException: 事务不是与当前连接无关联，就是已完成。

请问如何解决？

Answer 1

你要把你的Execute()这个方法的源代码贴出来。。。

Answer 2

不好意思，相关代码如下   

 public static object Execute(SqlTransaction trans, string cmdText, params SqlParameter[] commandParameters)
        {
            SqlCommand cmd = new SqlCommand();
            PrepareCommand(cmd, trans.Connection,trans, cmdText, commandParameters);
            object val = cmd.ExecuteScalar();
            cmd.Parameters.Clear();
            return val;
        }

public static int ExecuteNonQuery(SqlTransaction trans, string cmdText, params SqlParameter[] commandParameters)
        {
            SqlCommand cmd = new SqlCommand();
            PrepareCommand(cmd, trans.Connection, trans, cmdText, commandParameters);
            int val = cmd.ExecuteNonQuery();
            cmd.Parameters.Clear();
            return val;
        }

  private static void PrepareCommand(SqlCommand cmd, SqlConnection conn, SqlTransaction trans, string cmdText, SqlParameter[] cmdParms)
        {

            //判断数据库连接状态
            if (conn.State != ConnectionState.Open)
                conn.Open();

            cmd.Connection = conn;
            cmd.CommandText = cmdText;

            //判断是否需要事物处理
            if (trans != null)
                cmd.Transaction = trans;

            cmd.CommandType = CommandType.Text;

            if (cmdParms != null)
            {
                foreach (SqlParameter parm in cmdParms)
                    cmd.Parameters.Add(parm);
            }
        }

Answer 3

呵呵，贴下代码，发现问题了，原来一个地方使用了另外的SqlConnnection