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New Message on BDOTNET
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From: chocoGee
Message 2 in Discussion
Hi, I think these couple of sentences will make it clear. Transactions are a group
of database operations combined into a logical unit of work, and are used to control
and maintain the consistency and integrity of each database despite errors that might
occur in the system. A transaction consists of a series of SQL SELECT, INSERT, UPDATE,
or DELETE statements. If no errors are encountered during a transaction, all
modifications in the transaction become a permanent part of the database. If errors
are encountered, none of the modifications are made to the database.
For example, in a banking application where funds are transferred from one account to
another, one account is credited an amount, and another account is debited the same
amount at the same time. Because computers can fail due to power outages, network
outages, and so on, it is possible to update a row in one table, but not in the
related table. If your database supports transactions, you can group database
operations into a transaction to prevent database inconsistency resulting from these
events.
There are three basic commands for transactions: BEGIN, COMMIT, and ROLLBACK. The
BEGIN statement marks the beginning of a transaction. All procedures attempted after
the BEGIN statement are considered part of the transaction, which is completed by the
COMMIT statement, or canceled by the ROLLBACK statement.
The following example demonstrates transactional logic using Transact-SQL.BEGIN TRAN
INSERT INTO account (account,amount,debitcredit) values (100,100,'d') INSERT INTO
account (account,amount,debitcredit) values (300,100,'c') IF (@@ERROR > 0) ROLLBACK
ELSE COMMIT
In ADO.NET, you control transactions using the Connection and Transaction objects.
To perform a transaction Call the BeginTransaction method of the Connection
object to mark the start of the transaction. BeginTransaction returns a reference to
the Transaction. Retain this reference so that you can assign it to Commands that are
enlisted in the transaction. Assign the Transaction object to the Transaction
property of the Command to be executed. If a Command is executed on a Connection with
an active Transaction and the Transaction object has not been assigned to the
Transaction property of the Command, an exception will be thrown. Execute the
required commands. Call the Commit method of the Transaction object to
complete the transaction, or call the Rollback method to cancel the transaction.
The following code example demonstrates transactional logic using ADO.NET with
Microsoft� SQL Server�.[Visual Basic] Dim myConnection As SqlConnection = New
SqlConnection("Data Source=localhost;Initial Catalog=Northwind;Integrated
Security=SSPI;") myConnection.Open() ' Start a local transaction. Dim myTrans As
SqlTransaction = myConnection.BeginTransaction() ' Enlist the command in the current
transaction. Dim myCommand As SqlCommand = New SqlCommand myCommand.Transaction =
myTrans Try myCommand.CommandText = "Insert into Region (RegionID,
RegionDescription) VALUES (100, 'Description')" myCommand.ExecuteNonQuery()
myCommand.CommandText = "Insert into Region (RegionID, RegionDescription) VALUES (101,
'Description')" myCommand.ExecuteNonQuery() myTrans.Commit()
Console.WriteLine("Both records are written to database.") Catch e As Exception
myTrans.Rollback() Console.WriteLine(e.ToString()) Console.WriteLine("Neither
record was written to database.") Finally myConnection.Close() End Try Rgds,Geetha
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