10 理解事务

10.1 什么是事务

10.2 创建事务

10.2.1 使用T-SQL创建事务

 

SET  XACT_ABORT  ON
BEGIN  TRY
     BEGIN   TRANSACTION
     -- work code here
     COMMIT   TRANSACTION
END  TRY
BEGIN  CATCH
     ROLLBACK   TRANSACTION
     -- cleanup code
END  CATCH

 

10.2.2 使用DbTransaction对象创建事务

 

代码

Imports  System.Configuration
Imports  System.Data.SqlClient
Public   Class  Form1
     Private   Sub  Button1_Click( ByVal  sender  As  System.Object,
                               ByVal  e  As  System.EventArgs)  Handles  Button1.Click
         Dim  cnSetting  As  ConnectionStringSettings  =
            ConfigurationManager.ConnectionStrings( " NorthwindString " )
         Using  cn  As   New  SqlConnection
            cn.ConnectionString  =  cnSetting.ConnectionString
            cn.Open()
             Using  tran  As  SqlTransaction  =  cn.BeginTransaction
                 Try
                     ' work code here
                     Using  cmd  As  SqlCommand  =  cn.CreateCommand
                        cmd.Transaction  =  tran
                        cmd.CommandText  =   " SELECT COUNT(*) FROM employees "
                         Dim  count  As   Integer   =   CInt (cmd.ExecuteScalar)
                        MessageBox.Show(count.ToString)
                     End   Using
                     ' if we made it this far, commit
                    tran.Commit()
                 Catch  ex  As  Exception
                    tran.Rollback()
                     ' cleanup code
                    MessageBox.Show(ex.Message)
                 End   Try
             End   Using
         End   Using
     End Sub
End Class

 

 

10.3 设置事务的孤立级别

SET   TRANSACTION   ISOLATION   LEVEL   REPEATABLE   READ

 

添加查询提示设置事务的孤立级别

SELECT   *   FROM  CUSTOMERS  WITH  (NOLOCK)

 

在SqlTransaction类上设置事务孤立级别。

代码

     Private   Sub  Button2_Click( ByVal  sender  As  System.Object,
                               ByVal  e  As  System.EventArgs)  Handles  Button2.Click
         Dim  cnSetting  As  ConnectionStringSettings  =
            ConfigurationManager.ConnectionStrings( " NorthwindString " )
         Using  cn  As   New  SqlConnection
            cn.ConnectionString  =  cnSetting.ConnectionString
            cn.Open()
             Using  tran  As  SqlTransaction  =
                cn.BeginTransaction(System.Data.IsolationLevel.Serializable)
                 Try
                     ' work code here
                     Using  cmd  As  SqlCommand  =  cn.CreateCommand
                        cmd.Transaction  =  tran
                        cmd.CommandText  =   " SELECT COUNT(*) FROM employees "
                         Dim  count  As   Integer   =   CInt (cmd.ExecuteScalar)
                        MessageBox.Show(count.ToString)
                     End   Using
                     ' if we made it this far, commit
                    tran.Commit()
                 Catch  ex  As  Exception
                    tran.Rollback()
                     ' cleanup code
                    MessageBox.Show(ex.Message)
                 End   Try
             End   Using
         End   Using
     End Sub

  

10.4 System.Transactions命名空间

10.4.1 使用TransactionScope类创建事务

 

代码

Imports  System.Transactions

     Private   Sub  Button3_Click( ByVal  sender  As  System.Object,
                               ByVal  e  As  System.EventArgs)  Handles  Button3.Click
         Dim  cnSetting  As  ConnectionStringSettings  =
            ConfigurationManager.ConnectionStrings( " NorthwindString " )
         Using  ts  As   New  TransactionScope
             Using  cn  As   New  SqlConnection
                cn.ConnectionString  =  cnSetting.ConnectionString
                cn.Open()
                 ' work code here
                 Using  cmd  As  SqlCommand  =  cn.CreateCommand
                    cmd.CommandText  =   " SELECT COUNT(*) FROM employees "
                     Dim  count  As   Integer   =   CInt (cmd.ExecuteScalar)
                    MessageBox.Show(count.ToString)
                 End   Using
                 ' if we made it this far, commit
                ts.Complete()
             End   Using
         End   Using
     End Sub

 

10.4.2 设置事务选项

 

代码

     Private   Sub  Button4_Click( ByVal  sender  As  System.Object,
                               ByVal  e  As  System.EventArgs)  Handles  Button4.Click
         Dim  cnSetting  As  ConnectionStringSettings  =
            ConfigurationManager.ConnectionStrings( " NorthwindString " )
         Dim  opt  As   New  TransactionOptions
        opt.IsolationLevel  =  IsolationLevel.Serializable
         Using  ts  As   New  TransactionScope(TransactionScopeOption.Required, opt)
             Using  cn  As   New  SqlConnection
                cn.ConnectionString  =  cnSetting.ConnectionString
                cn.Open()
                 ' work code here
                 Using  cmd  As  SqlCommand  =  cn.CreateCommand
                    cmd.CommandText  =   " SELECT COUNT(*) FROM employees "
                     Dim  count  As   Integer   =   CInt (cmd.ExecuteScalar)
                    MessageBox.Show(count.ToString)
                 End   Using
             End   Using
             ' if we made it this far, commit
            ts.Complete()
         End   Using
     End Sub

 

10.4.3 处理分布式事务

10.4.4 建立自己的事务资源管理器