基于TransactionScope类的分布式隐式事务

System.Transactions 命名空间中除了上一节中提到的基于 Transaction 类的显式编程模型，还提供使用 TransactionScope 类的隐式编程模型，它与显示编程模型相比，更加方便简单，它也是MSDN中建议使用的编程模型。

下面，我们基于TransactionScope类实现上一节银行转帐的例程。

示例代码：

（1）SqlHelper.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Configuration;
using MySql.Data.MySqlClient;
using System.Transactions;
using System.Data;

namespace 事务处理
{
    public class SqlHelper
    {
        public static string GetConnection()
        {
            string connStr = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
            return connStr;
        }

        public static int ExecuteNonQuery(string sql, params MySqlParameter[] parameters)
        {
            int result = -1;
            using (MySqlConnection conn = new MySqlConnection(GetConnection()))
            {
                conn.Open();

                using (MySqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = sql;
                    cmd.Parameters.AddRange(parameters);
                    result = cmd.ExecuteNonQuery();
                }
            }
            return result;
        }

        public static DataTable ExecuteDataTable(string sql, params MySqlParameter[] parameters)
        {
            using (MySqlConnection conn = new MySqlConnection(GetConnection()))
            {
                using (MySqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = sql;
                    cmd.Parameters.AddRange(parameters);
                    using (MySqlDataAdapter da = new MySqlDataAdapter(cmd))
                    {
                        using (DataSet ds = new DataSet())
                        {
                            da.Fill(ds);
                            return ds.Tables[0];
                        }
                    }
                }
            }
        }
    }

}

（2）Bankaccountn.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using MySql.Data.MySqlClient;
using System.Data;
using System.Transactions;

namespace 事务处理
{
    public class Bankaccountn
    {
        public Bankaccountn(string bankaccountnId)
        {
            string sql = @"SELECT * FROM Bankaccountn WHERE BankaccountnId=@BankaccountnId;";
            DataTable dt = SqlHelper.ExecuteDataTable(sql, new MySqlParameter("@BankaccountnId", bankaccountnId));
            if (dt.Rows.Count <= 0)
            {
                throw new Exception("账户不存在！");
            }
            else if (dt.Rows.Count > 1)
            {
                throw new Exception("异常信息：有重名的账户存在！");
            }
            else
            {
                this.bankaccountnId = dt.Rows[0]["BankaccountnId"] as string;
                this.UserName = dt.Rows[0]["UserName"] as string;
                this.Balance = Convert.ToDecimal(dt.Rows[0]["Balance"]);
            }
        }

        private string bankaccountnId;
        public string UserName
        {
            get;
            private set;
        }
        public decimal Balance
        {
            get;
            private set;
        }

        protected int Update()
        {
            string sql = @"UPDATE bankaccountn SET UserName = @UserName,Balance = @Balance
                           WHERE BankaccountnId= @BankaccountnId;";
            return SqlHelper.ExecuteNonQuery(sql, new MySqlParameter("@BankaccountnId", this.bankaccountnId), new MySqlParameter("@UserName", this.UserName), new MySqlParameter("@Balance", this.Balance));

        }
        public void Epend( decimal money)
        {
            this.Balance -= money;
            this.Update();
        }
        public void Income(decimal money)
        {
            this.Balance += money;
            this.Update();

        }
        public bool HiddenTransferOfAccount(string incomeBankaccountnId, decimal money)
        {
            bool result = true;
            using (TransactionScope scope = new TransactionScope())
            {
                try
                {
                    Bankaccountn incomeBankaccountn = new Bankaccountn(incomeBankaccountnId);
                    incomeBankaccountn.Income(money); //收款账户入账
                    this.Epend(money); //付款账户支出
                    scope.Complete();
                }
                catch (Exception ex)
                {
                    //这里写做异常信息的记录的代码
                    result = false;
                }
            }
            return result;
        }
    }

}

（3）测试代码

Bankaccountn one = new Bankaccountn("6666660123456789");
if (one.HiddenTransferOfAccount("6666669876543210", 200M))
{
    Response.Write("<script>alert('转账成功')</script>");
}
else
{
    Response.Write("<script>alert('转账失败')</script>");
}

代码分析：

使用TransactionScope 之后，事务管理器会 预执行代码，直至Complete()处，如果过程没有出错，这通知事务管理器去提交，如果错误就不提交，保证了整个执行过程的一致性。

但，在使用隐式编程模型时应注意以下几点：

1）要确保参与事务的资源（如连接的打开等）的全登记放在TransactionScope 实例化对象之后，调用Complete()方法之前。

2）从TransactionScope 实例化到调用Complete()方法之间的代码，不要吃掉异常。

using (TransactionScope scope = new TransactionScope())
{
    try
    {
        //要确保参与事务的资源全部登记在这个位置（如连接的打开等）
         Bankaccountn incomeBankaccountn = new Bankaccountn(incomeBankaccountnId);
         incomeBankaccountn.Income(money); //收款账户入账
         this.Epend(money); //付款账户支出
         scope.Complete();
    }
    catch (Exception ex)
    {
         //捕获异常要在这个位置
          result = false;
    }
}

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