How to use SqlTransaction in C#

Question

I am using the following code to execute two commands at once. I used SqlTransaction to assure either all command get executed or rolled back. When I run my program without "transaction", it runs properly; but when I use "transaction" with them, they show error.

My code:

SqlTransaction transaction = connectionsql.BeginTransaction();
            
try
{
    SqlCommand cmd1 = new SqlCommand("select account_name from master_account where NOT account_name = 'BANK' AND NOT account_name = 'LOAN'", connectionsql);
    SqlDataReader dr1 = cmd1.ExecuteReader();
    while (dr1.Read())
    {
        comboBox1.Items.Add(dr1[0].ToString().Trim());
    }
    cmd1.Dispose();
    dr1.Dispose();

    SqlCommand cmd2 = new SqlCommand("select items from rate",connectionsql);
    SqlDataReader dr2 = cmd2.ExecuteReader();
    while (dr2.Read())
    {
        comboBox2.Items.Add(dr2[0].ToString().Trim());
    }
    cmd2.Dispose();
    dr2.Dispose();
    transaction.Commit();

    dateTimePicker4.Value = dateTimePicker3.Value;
}
catch(Exception ex)
{
    transaction.Rollback();
    MessageBox.Show(ex.ToString());
}

Error:

Answer 1

You have to tell your SQLCommand objects to use the transaction:

cmd1.Transaction = transaction;

or in the constructor:

SqlCommand cmd1 = new SqlCommand("select...", connectionsql, transaction);

Make sure to have the connectionsql object open, too.

But all you are doing are SELECT statements. Transactions would benefit more when you use INSERT, UPDATE, etc type actions.

Answer 2

The following example creates a SqlConnection and a SqlTransaction. It also demonstrates how to use the BeginTransaction, Commit, and Rollback methods. The transaction is rolled back on any error, or if it is disposed without first being committed. Try/Catch error handling is used to handle any errors when attempting to commit or roll back the transaction.

private static void ExecuteSqlTransaction(string connectionString)
{
    using (SqlConnection connection = new SqlConnection(connectionString))
    {
        connection.Open();

        SqlCommand command = connection.CreateCommand();
        SqlTransaction transaction;

        // Start a local transaction.
        transaction = connection.BeginTransaction("SampleTransaction");

        // Must assign both transaction object and connection 
        // to Command object for a pending local transaction
        command.Connection = connection;
        command.Transaction = transaction;

        try
        {
            command.CommandText =
                "Insert into Region (RegionID, RegionDescription) VALUES (100, 'Description')";
            command.ExecuteNonQuery();
            command.CommandText =
                "Insert into Region (RegionID, RegionDescription) VALUES (101, 'Description')";
            command.ExecuteNonQuery();

            // Attempt to commit the transaction.
            transaction.Commit();
            Console.WriteLine("Both records are written to database.");
        }
        catch (Exception ex)
        {
            Console.WriteLine("Commit Exception Type: {0}", ex.GetType());
            Console.WriteLine("  Message: {0}", ex.Message);

            // Attempt to roll back the transaction. 
            try
            {
                transaction.Rollback();
            }
            catch (Exception ex2)
            {
                // This catch block will handle any errors that may have occurred 
                // on the server that would cause the rollback to fail, such as 
                // a closed connection.
                Console.WriteLine("Rollback Exception Type: {0}", ex2.GetType());
                Console.WriteLine("  Message: {0}", ex2.Message);
            }
        }
    }
}

See SqlTransaction Class

Answer 3

You can create a SqlTransaction from a SqlConnection.

And use it to create any number of SqlCommands

SqlTransaction transaction = connection.BeginTransaction();
var cmd1 = new SqlCommand(command1Text, connection, transaction);
var cmd2 = new SqlCommand(command2Text, connection, transaction);

Or

var cmd1 = new SqlCommand(command1Text, connection, connection.BeginTransaction());
var cmd2 = new SqlCommand(command2Text, connection, cmd1.Transaction);

---

If the failure of commands never cause unexpected changes don't use transaction.

if the failure of commands might cause unexpected changes put them in a Try/Catch block and rollback the operation in another Try/Catch block.

Why another try/catch? According to MSDN:

Try/Catch exception handling should always be used when rolling back a transaction. A Rollback generates an InvalidOperationException if the connection is terminated or if the transaction has already been rolled back on the server.

Here is a sample code:

string connStr = "[connection string]";
string cmdTxt = "[t-sql command text]";

using (var conn = new SqlConnection(connStr))
{
    conn.Open();
    var cmd = new SqlCommand(cmdTxt, conn, conn.BeginTransaction());
    

    try
    {
        cmd.ExecuteNonQuery();
        //before this line, nothing has happened yet
        cmd.Transaction.Commit();
    }
    catch(System.Exception ex)
    {
        //You should always use a Try/Catch for transaction's rollback
        try
        {
            cmd.Transaction.Rollback();
        }
        catch(System.Exception ex2)
        {
            throw ex2;
        }
        throw ex;
    }

    conn.Close();
}

The transaction is rolled back in the event it is disposed before Commit or Rollback is called.

So you don't need to worry about app being closed.

Answer 4

Well, I don't understand why are you used transaction in case when you make a select.

Transaction is useful when you make changes (add, edit or delete) data from database.

Remove transaction unless you use insert, update or delete statements