A Look into Transactions in ADO.NET 2.0
 
Published: 15 Mar 2006
Unedited - Community Contributed
Abstract
In this article, we will look into how to manage transactions against SQL Server in ADO.NET 2.0.
by Mohammad Azam
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Introduction

We all have used transactions in one way or the other. In this article, I will show you how you can make use of the SqlTransaction class, which is introduced in ADO.NET 2.0.

What are Transactions?

A transaction is a set of operations in which either all of them are successful or all of them fail to ensure consistency. A simple example of a transaction is when you go to the bank and deposit some amount of money and then transfer your deposited amount to another bank account. In this case, all the operations must be performed for the transaction to be valid. This means that if your amount is not deposited and there is not enough money in your bank account, then there will be an error in transferring the funds. For this reason, we use transactions so that either all the operations are performed or none of them are.

Creating a Simple Transaction

Since we now have the basic idea of what a transaction is, let’s take a look at how we can use transactions using ADO.NET 2.0. We are going to implement the AddUser method, which will add a new user to the database, and if the insertion operation is successful, then we will assign the role to the newly added user and add him in the role database. Below you can see a screen shot of the database diagram.

 

As you can see, the above database is pretty simple and only consists of two tables, Users and UserRoles. Now let’s see the code that inserts data into the tables.

Listing 1 – AddUser() Method

public static bool AddUser(string firstName,string lastName)
{
  bool result = false;
 
  SqlConnection myConnection = newSqlConnection(ConnectionString);
  SqlTransaction myTransaction = null;
 
  SqlCommand myCommand = newSqlCommand(SP_INSERT_USER, myConnection);
  myCommand.CommandType =CommandType.StoredProcedure;
 
 myCommand.Parameters.AddWithValue("@FirstName", firstName);
 myCommand.Parameters.AddWithValue("@LastName", lastName);
  myCommand.Parameters.Add("@ReturnValue",SqlDbType.Int, 4);
 myCommand.Parameters["@ReturnValue"].Direction =
    ParameterDirection.ReturnValue;
 
  try
  {
    myConnection.Open();
    myTransaction =myConnection.BeginTransaction();
    myCommand.Transaction = myTransaction;
 
    myCommand.ExecuteNonQuery();
    int returnValue =(int)myCommand.Parameters["@ReturnValue"].Value;
 
    if (returnValue <= 0)
      throw newArgumentOutOfRangeException("Value not inserted.");
 
    myCommand.Parameters.Clear();
    myCommand.CommandText = SP_INSERT_USER_ROLE;
    myCommand.CommandType =CommandType.StoredProcedure;
   myCommand.Parameters.AddWithValue("@UserID", returnValue);
    myCommand.ExecuteNonQuery();
 
    result = true;
 
  }
  catch (Exception ex)
  {
    string exception = ex.Message;
    myTransaction.Rollback();
  }
 
  finally
  {
    myTransaction.Commit();
    myConnection.Close();
    myCommand.Dispose();
  }
 
  return result;
 
}

Analysis

Let’s see what is going on inside the AddUser() method. As you can see, the method takes two parameters, which are FirstName and LastName. I have created the SqlConnection object, SqlCommand object, and the SqlTransaction object. Later, I attached the parameters to the command object. The important part is when the connection opens and we begin our transaction. Take a look at the code below.

Listing 2 – Starting the Transaction

myConnection.Open();
myTransaction = myConnection.BeginTransaction();
myCommand.Transaction = myTransaction;

In the above code, I have first opened the database connection and then started the transaction using the BeginTransaction method of the connection object. After starting the transaction, I assigned the transaction to the command object. If the insertion in the Users table is successful, it will return the UserID of the newly inserted user. If that UserID is greater than 0, it means that the new user has been created successfully and we can proceed to our next task, which is to insert the role of that user into the UserRoles table. Check out the following code, which attaches the returnValue (returnValue contains the UserID) to the SqlCommand object.

Listing 3 – Inserting User Role in the UserRoles Table

myCommand.Parameters.Clear();
myCommand.CommandText = SP_INSERT_USER_ROLE;
myCommand.CommandType =CommandType.StoredProcedure;
myCommand.Parameters.AddWithValue("@UserID",returnValue);
myCommand.ExecuteNonQuery();

As you can see in the code above, first I clear the old parameters from the SqlCommand object, and then attach the new parameters.

If any exception is thrown, then we do a rollback using the myTransaction.Rollback(); method; else we commit the transaction using myTransaction.Commit();. This will ensure that the transaction is only committed when there is no exception thrown.

So, you see in the above example that we used Transactions, which I am sure you found simple. Now let’s take a look at some other stuff that comes along with Transactions.

Transaction Isolation Levels

There are different Isolation Levels in Transactions. The one that we demonstrated in the example above is known as ReadOnCommited, which means that you can read the newly inserted data only after the transaction is committed. Of course, if you rollback, you will not see the new record. The other important Isolation Level is ReadUnCommited, which is also known as “Dirty Reads”. Let’s see what “Dirty Reads” means.

Dirty Reads

Dirty Reads means that you are able to read the data that is being processed within the transaction and not yet committed or rolled back. This means that you might be able to view the information of a user who was never inserted in the database. Let’s see how we can implement "Dirty Reads" using ADO.NET 2.0 Transactions.

Implementing Dirty Reads

In this example, I will create two SqlConnections. I am creating two connections since in SQL SERVER 2000 you cannot have parallel transactions. Apart from making two connections, I will also make two SqlCommand objects. One command object will be used to insert a new user; the second command object will be used to read the inserted user. Each of the command objects will be accompanied with their own SqlTransaction objects.

Listing 4: AddUserDirtyRead() Method Implementation

public static bool AddUserDirtyRead(stringfirstName, string lastName)
{
  bool result = false;
 
  SqlTransaction myTransaction1 = null;
  SqlTransaction myTransaction2 = null;
 
  SqlConnection myConnection1 = newSqlConnection(ConnectionString);
  SqlConnection myConnection2 = new SqlConnection(ConnectionString);
 
  SqlCommand myCommand1 = newSqlCommand(SP_INSERT_USER, myConnection1);
  myCommand1.CommandType =CommandType.StoredProcedure;
 myCommand1.Parameters.AddWithValue("@FirstName", firstName);
  myCommand1.Parameters.AddWithValue("@LastName",lastName);
 
  SqlCommand myCommand2 = newSqlCommand("SELECT * FROM Users", myConnection2);
 
  try
  {
    myConnection1.Open();
    myConnection2.Open();
    myTransaction1 =myConnection1.BeginTransaction();
    myTransaction2 = myConnection2.BeginTransaction
      (IsolationLevel.ReadUncommitted);
 
    myCommand1.Transaction = myTransaction1;
    myCommand2.Transaction = myTransaction2;
 
    Console.WriteLine("Inserting newrecords into the database.");
    myCommand1.ExecuteNonQuery();
 
    SqlDataReader reader =myCommand2.ExecuteReader();
 
    Console.WriteLine("Reading uncommiteddata..");
    while (reader.Read())
    {
      if (reader.HasRows)
      {
        Console.WriteLine("FirstName:" + reader[1] + "," + "LastName:" +
          reader[2]);
      }
    }
 
    reader.Close();
 
    result = true;
  }
  catch (Exception ex)
  {
    string exception = ex.Message;
    myTransaction1.Rollback();
    myTransaction2.Rollback();
  }
 
  finally
  {
    myTransaction1.Commit();
    myTransaction2.Commit();
    myConnection1.Close();
    myConnection2.Close();
 
  }
 
  return result;
}

Analysis

As I mentioned in the example above, I created two SqlConnection, SqlCommand, and SqlTransaction objects. myCommand1 is used to insert a new user into the database table and myCommand2 is used to select all records from the database table. Both of the connections are open and the transactions are started. You will notice that I have set the transaction isolation level for the myTransaction2 object. Check out the code below.

Listing 5 – Setting the Transaction Isolation Level

myTransaction2 =myConnection2.BeginTransaction(IsolationLevel.ReadUncommitted);

Notice that I have executed the myCommand object but not committed the transaction. At this point I used the myCommand2 to run a SqlDataReader and return all the records in the table. Since I had set the transaction level to ReadUnCommitted, a newly inserted and uncommitted user will be returned and displayed on the screen. This is called a “Dirty Read” since we are reading data that is not yet committed.

Save Points in Transactions

Whenever you rollback a transaction, it rolls back all the operations that you have performed before. Sometimes you need to undo the transaction to a certain point. For this scenario, you can use the Save Points functionality. Save Points allows you to rollback a transaction to a certain point. Let’s take a look at code below, which uses a Save Point.

Listing 6 – Using Save Points in Transaction

public static void AddUserSavePointTransaction()
{
  SqlConnection myConnection = newSqlConnection(ConnectionString);
  SqlCommand myCommand = new SqlCommand();
  myCommand.CommandText = @
    "INSERT INTOUsers(FirstName,LastName)VALUES('John', 'Doe')
    ";myCommand.Connection = myConnection;
 
  SqlTransaction myTransaction = null;
 
  try
  {
    myConnection.Open();
    myTransaction =myConnection.BeginTransaction();
    myCommand.Transaction = myTransaction;
 
    myCommand.ExecuteNonQuery();
 
    myTransaction.Save("firstInsertUser");
 
    myCommand.CommandText = @
      "INSERT INTOUsers(FirstName,LastName)VALUES('Azam', 'Sharp')";
 
    myCommand.ExecuteNonQuery();
   myTransaction.Rollback("firstInsertUser");
  }
  catch (Exception ex)
  {
    string exception = ex.Message;
    myTransaction.Rollback();
  }
 
  finally
  {
    myTransaction.Commit();
    myConnection.Close();
 
  }
}

Analysis

As you can see in the code above, I am using the command object to insert a new user. After executing the command object for the first time, I create a save point and insert another user. Immediately after inserting the second user, I rollback the transaction to the save point. Since the save point is declared after first user is inserted, only the insertion of first user will succeed, and the insertion of the second user will be discarded.

[Download Sample]

Conclusion

In this article, I demonstrated how you can make use of the SqlTransaction class to support transactions in your applications. There are many different options and features that cannot be covered in one article; for this reason, I recommend that you check out www.msdn.microsoft.com for more details about the SqlTransaction class. 



User Comments

Title: feedback   
Name: programacion web
Date: 2010-11-22 11:07:36 AM
Comment:
excellent article, thanks
Title: feedback   
Name: suleman
Date: 2010-06-11 2:20:56 AM
Comment:
myTransaction.Commit();
is in finally block in listing 1 , that is wrong , it there is exception then transaction already rollback , and myTransaction.Commit() will also execute in finally block.

Can you Please verify.
Title: Where are the SP of this article   
Name: Rameez
Date: 2009-05-25 3:49:45 AM
Comment:
Hi,
Excellet work keep it up but where are the stored Procedure of this article let me know plz
Best Regards
Title: Very Nice Article   
Name: Krunal.Shaholia
Date: 2008-09-04 4:24:31 AM
Comment:
A very nice article .would like to see more interesting articles of this kind.
Title: easy understandable to any person   
Name: pralay mitra
Date: 2008-05-23 12:35:26 PM
Comment:
it' good. keep going
Title: keep it up   
Name: peddakapu
Date: 2007-12-04 3:02:24 AM
Comment:
Hi
Mohammad Azam......How r u? The way u r done is very nice.

keep it up ..young man..takecare...
Title: good explain   
Name: naidu
Date: 2007-12-04 2:59:24 AM
Comment:
Thanks...a lot....
Title: nice coding work   
Name: vijay
Date: 2007-12-03 5:13:36 AM
Comment:
the codeing work done by mr azam is very nice
Title: Very Nice   
Name: Irina
Date: 2007-10-30 12:52:12 PM
Comment:
Very clear and simple idea to demonstrate transaction in use. Can be easily modified to see results for other isolation level settings. Nice!
Title: Excellent   
Name: abc
Date: 2007-10-01 8:23:32 AM
Comment:
Excellent way of understanding the Transaction.
Title: Nice (Y)   
Name: Faraz Siddiqui
Date: 2007-09-26 1:38:55 PM
Comment:
Very easy way to understand the Transaction.
Title: SQL Transaction   
Name: Nitin Sharma(.Net Developer)
Date: 2007-07-02 6:33:23 AM
Comment:
The article is very very easy to understand...Keep it up..always...!!
Title: very good   
Name: Lalji Mer
Date: 2007-05-01 3:26:24 AM
Comment:
It is very nice to understand transaction process too.
Title: Very Good   
Name: Sivanthinathan
Date: 2007-03-16 4:42:52 AM
Comment:
It is very nice to understand transaction process.
Title: Very very good   
Name: Paul Gonzales
Date: 2007-01-19 1:01:02 PM
Comment:
My english isn't so good, but i understand all.. this article is excelent.
I'd like get more similar articles.
thanks
Lima-Peru
Title: good   
Name: nitin
Date: 2006-12-07 2:51:01 PM
Comment:
good work. keep it up
Title: GOOD Article   
Name: Rajesh Varma
Date: 2006-11-24 8:59:05 AM
Comment:
ITs Very good Articles...and well presented....
Title: gr8 job   
Name: Rajeev Kumar Shukla
Date: 2006-08-18 8:59:34 AM
Comment:
problem with finally block otherwise article is very good specialy regarding SavePoint in transaction.
Title: Knowledge shareable Article   
Name: Mahendra singh
Date: 2006-07-20 7:43:41 AM
Comment:
wow
that's great Article.
specially the way of explanation is Interesting
Title: Software Engineer   
Name: Premanshu Mukherji
Date: 2006-07-20 7:33:18 AM
Comment:
Very nice article. Dirty Read was well explained. Examples are self explanatory. Good Job.
Title: Best one   
Name: Sudhakar rao
Date: 2006-07-04 1:41:21 AM
Comment:
This article is best one ,i didnt c this type of article .
Thanks keep it up my friends
Title: Problem with IsolationLevel   
Name: Ctut
Date: 2006-04-28 5:42:54 PM
Comment:
The one that you demonstrated in the example above is not known as ReadOnCommited, it's known as a ReadCommitted.
Title: Problem with commit   
Name: Simon Stewart
Date: 2006-04-05 2:58:05 AM
Comment:
Please check your finally block.

You should rather call commit directly after you have done the DB operation.
In your case if an error occurs, your finally block will fail because the transaction is not in a usable state at that point.
Title: Programer Analyst   
Name: Srinivas
Date: 2006-03-23 6:51:56 AM
Comment:
Nice One for novice users
Title: Very Nice Work   
Name: Rupesh kumar Sinha
Date: 2006-03-22 12:52:12 AM
Comment:
Its a great work for them who wants to be updated in latest technology!! Keep it Up
Title: Thanks   
Name: Mohammad Azam
Date: 2006-03-21 7:59:41 PM
Comment:
Thank you very much everyone for your kind comments.
Title: Nicely Done!   
Name: strahman
Date: 2006-03-21 12:10:14 PM
Comment:
Very well written!! Excellent job, Azam!!
Title: Very Good   
Name: sree
Date: 2006-03-21 4:47:41 AM
Comment:
This Artcile is so Informative and Nice.






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