Local Transactions

Transactions in ADO.NET are used when you want to bind multiple tasks together so that they execute as a single unit of work. For example, imagine that an application performs two tasks. First, it updates a table with order information. Second, it updates a table that contains inventory information, debiting the items ordered. If either task fails, then both updates are rolled back.

A transaction is considered to be a local transaction when it is a single-phase transaction and is handled by the database directly. A transaction is considered to be a distributed transaction when it is coordinated by a transaction monitor and uses fail-safe mechanisms (such as two-phase commit) for transaction resolution.

Each of the .NET Framework data providers has its own Transaction object for performing local transactions. If you require a transaction to be performed in a SQL Server database, select a System.Data.SqlClient transaction. For an Oracle transaction, use the System.Data.OracleClient provider. In addition, there is a DbTransaction class that is available for writing provider-independent code that requires transactions.

In ADO.NET, you control transactions with the Connection object. You can initiate a local transaction with the BeginTransaction method. Once you have begun a transaction, you can enlist a command in that transaction with the Transaction property of a Command object. You can then commit or roll back modifications made at the data source based on the success or failure of the components of the transaction.

The scope of the transaction is limited to the connection. The following example performs an explicit transaction that consists of two separate commands in the try block. The commands execute INSERT statements against the Production.ScrapReason table in the AdventureWorks SQL Server sample database, which are committed if no exceptions are thrown. The code in the catch block rolls back the transaction if an exception is thrown. If the transaction is aborted or the connection is closed before the transaction has completed, it is automatically rolled back.

Follow these steps to perform a transaction.

1. Call the BeginTransaction method of the SqlConnection object to mark the start of the transaction. The BeginTransaction method returns a reference to the transaction. This reference is assigned to the SqlCommand objects that are enlisted in the transaction.

2. Assign the Transaction object to the Transaction property of the SqlCommand 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 object, an exception is thrown.

3. Execute the required commands.

4. Call the Commit method of the SqlTransaction object to complete the transaction, or call the Rollback method to end the transaction. If the connection is closed or disposed before either the Commit or Rollback methods have been executed, the transaction is rolled back.

The following code example demonstrates transactional logic using ADO.NET with Microsoft SQL Server.

using (SqlConnection connection = new(connectionString))
{
    connection.Open();

    // Start a local transaction.
    SqlTransaction sqlTran = connection.BeginTransaction();

    // Enlist a command in the current transaction.
    SqlCommand command = connection.CreateCommand();
    command.Transaction = sqlTran;

    try
    {
        // Execute two separate commands.
        command.CommandText =
          "INSERT INTO Production.ScrapReason(Name) VALUES('Wrong size')";
        command.ExecuteNonQuery();
        command.CommandText =
          "INSERT INTO Production.ScrapReason(Name) VALUES('Wrong color')";
        command.ExecuteNonQuery();

        // Commit the transaction.
        sqlTran.Commit();
        Console.WriteLine("Both records were written to database.");
    }
    catch (Exception ex)
    {
        // Handle the exception if the transaction fails to commit.
        Console.WriteLine(ex.Message);

        try
        {
            // Attempt to roll back the transaction.
            sqlTran.Rollback();
        }
        catch (Exception exRollback)
        {
            // Throws an InvalidOperationException if the connection
            // is closed or the transaction has already been rolled
            // back on the server.
            Console.WriteLine(exRollback.Message);
        }
    }
}

Using connection As New SqlConnection(connectionString)
    connection.Open()

    ' Start a local transaction.
    Dim sqlTran As SqlTransaction = connection.BeginTransaction()

    ' Enlist a command in the current transaction.
    Dim command As SqlCommand = connection.CreateCommand()
    command.Transaction = sqlTran

    Try
        ' Execute two separate commands.
        command.CommandText = _
          "INSERT INTO Production.ScrapReason(Name) VALUES('Wrong size')"
        command.ExecuteNonQuery()
        command.CommandText = _
          "INSERT INTO Production.ScrapReason(Name) VALUES('Wrong color')"
        command.ExecuteNonQuery()

        ' Commit the transaction
        sqlTran.Commit()
        Console.WriteLine("Both records were written to database.")

    Catch ex As Exception
        ' Handle the exception if the transaction fails to commit.
        Console.WriteLine(ex.Message)

        Try
            ' Attempt to roll back the transaction.
            sqlTran.Rollback()

        Catch exRollback As Exception
            ' Throws an InvalidOperationException if the connection
            ' is closed or the transaction has already been rolled
            ' back on the server.
            Console.WriteLine(exRollback.Message)
        End Try
    End Try
End Using

• Transactions and Concurrency
• Distributed Transactions
• System.Transactions Integration with SQL Server
• ADO.NET Overview