Recipe 13.6. Using Transactions

Problem

You need to issue multiple database updates in the context of a single, atomic transaction.

Solution

Use an ADO.NET transaction to envelop the various SQL statements that need to be processed as a unit.

Discussion

The following block of code connects to a database via ADO.NET and makes several database updates within a single transaction:

 ' ----- Connect to the database. Dim connectionString As String = _    "Data Source=MySystem\SQLEXPRESS;" & _    "Initial Catalog=MyDatabase;Integrated Security=true" Dim theDatabase As New SqlClient.SqlConnection(connectionString) theDatabase.Open( ) ' ----- Create a command object that will hold each '       processed SQL statement. Dim sqlStatement As New SqlClient.SqlCommand sqlStatement.Connection = theDatabase ' ----- Start the transaction. Dim theTransaction As System.Data.SqlClient.SqlTransaction theTransaction = theDatabase.BeginTransaction( ) sqlStatement.Transaction = theTransaction ' ----- Issue the first statement. sqlStatement.CommandText = _    "UPDATE Table1 SET Column2 = 25 WHERE Column1 = 0" sqlStatement.ExecuteNonQuery( ) ' ----- Issue the second statement. sqlStatement.CommandText = _    "UPDATE Table1 SET Column2 = 50 WHERE Column1 = 1" sqlStatement.ExecuteNonQuery( ) ' ----- Finish the transaction. theTransaction.  Commit( ) ' ----- Clean up. theTransaction = Nothing sqlStatement = Nothing theDatabase.Close( ) theDatabase.Dispose( ) 

Transactions allow multiple SQL statements to exhibit all-or-nothing behavior. The ADO.NET transaction object is provider-specific and communicates with the target database to manage the atomic nature of the multi-statement transaction.

The SqlTransaction object establishes a transaction for a set of statements in SQL Server. Instead of creating the object directly, use the connection's BeginTransaction() method to create it. This establishes the new transaction at the database level:

 Dim theTransaction As System.Data.SqlClient.SqlTransaction theTransaction = theDatabase.BeginTransaction() 

All commands issued while the transaction is in effect need to include the transaction object. Assign the object to each command's transaction property:

 sqlStatement.Transaction = theTransaction 

When you have issued all the commands needed for this transaction, use the transaction object's Commit() method to permanently write all updates to the database:

 theTransaction.Commit() 

If for any reason you need to cancel the changes in the middle of the transaction, use the Rollback() method instead:

 theTransaction.Rollback()