Database, Using Transaction

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()