事务是一组组合成逻辑工作单元的数据库操作,虽然系统中可能会出错,但事务将控制和维护每个数据库的一致性和完整性。如果在事务过程中没有遇到错误,事务中的所有修改都将永久成为数据库的一部分。如果遇到错误,则不会对数据库作出任何修改。
例如,在一个银行应用程序中,如果资金从一个帐户转到另一个帐户,则会将一定的金额记入一个帐户的贷方,同时将相同的金额记入另一个帐户的借方。由于计算机可能会因为停电、网络中断等原因而出现故障,所以有可能更新了一个表中的行,但没有更新相关表中的行。如果数据库支持事务,则可以将数据库操作组成一个事务,以防止因这些事件而使数据库出现不一致。
在 ADO.NET 中,可以使用 Connection 和 Transaction 对象来控制事务。若要执行事务,请执行下列操作:
调用 Connection 对象的 BeginTransaction 方法来标记事务的开始。BeginTransaction 返回对 Transaction 的引用。请保留此引用,以便将其分配给在事务中登记的 Command。
将 Transaction 对象分配给要执行的 Command 的 Transaction 属性。如果通过活动的 Transaction 对象对 Connection 执行 Command,但该 Transaction 对象尚未分配给 Command 的 Transaction 属性,则将引发异常。
执行所需的命令。
调用 Transaction 对象的 Commit 方法来完成事务,或调用 Rollback 方法来取消事务。
以下代码示例使用 Microsoft SQL Developer Network上的 ADO.NET 实例来演示事务逻辑。
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SqlConnection myConnection = new SqlConnection("Data Source=localhost;Initi Catalog=Northwind;Integrated Security=SSPI;");
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myConnection.Open();
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SqlTransaction myTrans = myConnection.BeginTransaction();// 启动一个事务
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SqlCommand myCommand = new SqlCommand();// 为事务创建一个命令
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myCommand.Connection=myConnection;
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myCommand.Transaction = myTrans;
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try
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{
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myCommand.CommandText = "Insert into Region (RegionID, RegionDescription) VALUES (100, "Description")";
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myCommand.ExecuteNonQuery();
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myCommand.CommandText = "Insert into Region (RegionID, RegionDescription) VALUES (101, "Description")";
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myCommand.ExecuteNonQuery();
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myTrans.Commit();//提交事务
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Response.Write("Both records are written to database.两次插入数据都成功");
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}
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catch(Exception e)
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{
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myTrans.Rollback();//回滚事务
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Response.Write(e.ToString());
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Response.Write("Neither record was written to database.没有一次插入数据成功");
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}
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finally
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{
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myConnection.Close();
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}
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