Transactions are a fundamental concept in database management, ensuring data integrity by allowing a series of operations to be treated as a single, atomic unit. If any part of the transaction fails, the entire transaction is rolled back, leaving the database in its original state. ADO.NET provides robust support for managing database transactions through its transaction objects.

Understanding Database Transactions

A database transaction adheres to the ACID properties:

• Atomicity: All operations within a transaction are completed successfully, or none of them are.
• Consistency: A transaction brings the database from one valid state to another.
• Isolation: Concurrent transactions do not interfere with each other.
• Durability: Once a transaction is committed, its changes are permanent, even in the event of system failure.

In ADO.NET, transactions are managed using the DbTransaction class and its provider-specific implementations (e.g., SqlTransaction for SQL Server).

Managing Transactions with ADO.NET

The process of managing a transaction typically involves the following steps:

1. Open a connection: Establish a connection to the database.
2. Begin the transaction: Call the BeginTransaction() method on the connection object. This returns a transaction object.
3. Execute commands: Associate DbCommand objects with the transaction. This ensures that commands are executed as part of the transaction.
4. Commit or Rollback:
   • If all operations are successful, call the Commit() method on the transaction object.
   • If an error occurs, call the Rollback() method on the transaction object.
5. Close the connection: Release the database connection.

Example: Using a Transaction with SQL Server

The following C# code demonstrates how to use a SqlTransaction to perform a series of database operations:

using System;
using System.Data.SqlClient;

public class TransactionExample
{
    public static void Main(string[] args)
    {
        string connectionString = "Server=myServerAddress;Database=myDataBase;User ID=myUsername;Password=myPassword;";

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

            try
            {
                // Begin the transaction
                transaction = connection.BeginTransaction();

                // Create commands and associate them with the transaction
                SqlCommand command1 = new SqlCommand("UPDATE Accounts SET Balance = Balance - 100 WHERE AccountId = 1", connection, transaction);
                command1.ExecuteNonQuery();

                SqlCommand command2 = new SqlCommand("UPDATE Accounts SET Balance = Balance + 100 WHERE AccountId = 2", connection, transaction);
                command2.ExecuteNonQuery();

                // If both commands succeed, commit the transaction
                transaction.Commit();
                Console.WriteLine("Transaction committed successfully.");
            }
            catch (Exception ex)
            {
                // If an error occurs, roll back the transaction
                if (transaction != null)
                {
                    transaction.Rollback();
                    Console.WriteLine("Transaction rolled back. Error: " + ex.Message);
                }
            }
            finally
            {
                // Ensure connection is closed
                if (connection.State == System.Data.ConnectionState.Open)
                {
                    connection.Close();
                }
            }
        }
    }
}
            

Transaction Isolation Levels

ADO.NET allows you to specify the isolation level for your transactions. The isolation level determines the degree to which one transaction must be isolated from the data modifications made by other concurrent transactions. Common isolation levels include:

• ReadUncommitted: Lowest isolation level. Reads may include uncommitted data.
• ReadCommitted: Reads only include data that has been committed.
• RepeatableRead: Guarantees that if a transaction reads a row multiple times, it will see the same row each time.
• Serializable: Highest isolation level. Ensures that transactions are executed as if they were run one after another, preventing all concurrency conflicts.

You can specify the isolation level when calling BeginTransaction():

SqlTransaction transaction = connection.BeginTransaction(System.Data.IsolationLevel.RepeatableRead);
            

Best Practices

• Keep transactions as short as possible to minimize lock times.
• Handle exceptions and ensure Rollback() is called if an error occurs.
• Use using statements for connections, commands, and transactions for automatic resource management.
• Choose an appropriate isolation level based on your application's requirements for concurrency and data consistency.