A Look into Transactions in ADO.NET 2.0
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by Mohammad Azam
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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.


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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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