Ado.net session10

Slide 1 of 31Ver. 1.0

Developing Database Applications Using ADO.NET and XML

Session 10

In this session, you will learn to:Manage local transactions

Manage distributed transactions

Objectives



Session 10

A transaction can be defined as a sequence of operations that are performed together as a single logical unit of work.

If a transaction is successful, all the data modifications performed in the database will be committed and saved.

If a transaction fails or an error occurs, then the transaction is rolled back to undo the data modifications done in the database.

Managing Local Transactions



Session 10

For a transaction to commit successfully within a database, it should possess the following four properties:

Atomicity

Consistency

Isolation

Durability

Properties of a Transaction

States that either all the modifications are performed or none of them are performed

States that data is in a consistent state after a transaction is completed successfully to maintain the integrity of data

States that any data modification made by one transaction must be isolated from the modifications made by the other transaction

States that any change in data by a completed transaction remains permanently in effect in the database



Session 10

ADO.NET provides support for two types of transactions:Local transactions

Distributed transactions

Types of Transaction

A local transaction performs on a single data source. Because local transactions are performed on a single data source, these transactions are efficient to operate and easy to manage.

A distributed transaction performs on multiple data sources. Distributed transactions enable you to incorporate several distinct transactional operations into an atomic unit that either succeed or fail completely.



Session 10

ADO.NET has an interface, IDbTransaction that contains methods for creating and performing local transactions against a single data source.

The following table lists the transaction classes available in the .NET Framework 2.0.

Performing Local Transactions

Types of Transaction Classes Description

System.Data.SqlClient.SqlTransaction Transaction class for .NET framework data provider for SQL Server

System.Data.OleDb.OleDbTransaction Transaction class for .NET framework data provider for OLE DB

System.Data.Odbc.OdbcTransaction Transaction class for .NET framework data provider for ODBC

System.Data.OracleClient.OracleTransaction Transaction class for .NET framework data provider for Oracle



Session 10

Let us understand how to create a local transaction.string connectString =

"Initial Catalog=AdventureWorks; Data Source=SQLSERVER01;User id=sa;Password=niit#1234";

SqlConnection cn = new SqlConnection();

cn.Open();

cn = connectString;

SqlTransaction tran = null;

Performing Local Transactions (Contd.)

Creating a connection to the data source



Session 10

try

{

tran = cn.BeginTransaction();SqlCommand cmd = new SqlCommand("INSERT INTOempdetails(ccode,cname, caddress,cstate,ccountry, cDesignation,cDepartment)VALUES(1101,'Linda Taylor', 'Oxfordshire','London','UK','Manager','Finance')", cn, tran);


Calling the BeginTransaction() methodCreating the command object and passing the SQL command



Session 10

cmd.ExecuteNonQuery();

tran.Commit();

Console.WriteLine("Transaction Committed\n)";

}

catch (SqlException ex)

{

tran.Rollback();

Console.WriteLine("Error - TRANSACTION ROLLED BACK\n" + ex.Message);

}


Committing the transaction if the command succeeds

Rolling back the transaction if the command fails



Session 10

catch (System.Exception ex)

{

Console.WriteLine("System Error\n" + ex.Message);

}

finally

{

cn.Close();

}

Console.ReadLine();

}

}

}




Session 10

Which method is called when a transaction succeeds in its operation?1. Rollback()

2. Commit()

3. BeginTransaction()

4. ExecuteNonQuery()

Just a minute

Answer:2. Commit()



Session 10

Problem Statement:John Howard, the HR executive has joined as a head of the Finance department at Texas. Therefore, his details need to be added to the HR database. The Department code for the Finance department is D002. The user name that needs to be assigned to him is JohnH and the password is howard.

As a part of the development team, you need to create a transaction that will allow you to add these details in the HRusers and Department tables.

Demo: Managing Local Transactions



Session 10

Distributed transactions are performed on multiple data sources or multiple connections within a data source.

Distributed transactions are created in the System.Transaction namespace.

The System.Transaction namespace has a TransactionScope class, which enables a developer to create and manage distributed transactions.

To create a distributed transaction, a TransactionScope object is created in a using block.

The TransactionScope object decides whether to create a local transaction or a distributed transaction. This is known as transaction promotion.

Managing Distributed Transactions



Session 10

Let us understand how to create a distributed transaction.using (TransactionScope ts = new TransactionScope())

{

using(SqlConnection cn = new SqlConnection("InitialCatalog=HR;Data Source=SQLSERVER01;Userid=sa;Password=niit#1234")){

cn.Open();

Managing Distributed Transactions (Contd.)

Creating a connection to the data source

Creating the TransactionScope object



Session 10

using(SqlCommand cmd = newSqlCommand("INSERT INTO HRusers(cUserName,cPassword)VALUES('Darren','Cooper')", cn))

{

int rowsUpdated =cmd.ExecuteNonQuery();if (rowsUpdated > 0)

{


Creating a SqlCommand object to insert a record in the HRusers table



Session 10

SqlConnection cn1 = newSqlConnection("Initial Catalog=HR;Data Source=SQLSERVER01;User id=sa;Password=niit#1234"))

{

cn1.Open();

using (SqlCommand cmd1 =new SqlCommand("DELETEDepartment WHEREcDepartmentCode=1111", cn1))

{

int rowsUpdated1 = cmd1.ExecuteNonQuery();


Creating another connection to the same data source

Creating another SqlCommand object to delete a record in the Department table



Session 10

if (rowsUpdated1 > 0)

{

ts.Complete();

Console.WriteLine("Transaction Committed\n");

cn1.Close();

}

}}}

cn.Close();

}}

Console.ReadLine();

}}}


Calling the Complete() method to commit the transactions



Session 10

The _______ method is invoked to commit the distributed transaction.1. Commit()

2. BeginTransaction()

3. Complete()

4. Rollback()

Just a minute

Answer:3. Complete()



Session 10

Bulk copy operations can be performed as an isolated operation or as a part of a transaction.

By default, a bulk copy operation is its own transaction.

To perform a bulk copy operation, you need to create a new instance of BulkCopy class with a connection string.

The bulk copy operation creates, and then, commits or rolls back the transaction.

Performing Bulk Copy Operations in a Transaction



Session 10

An isolation level determines the effect a transaction has on other transactions that are currently running, and vice versa.

By default, all transactions are completely isolated and run concurrently without impacting each other.

The isolation level of a transaction specifies the locking strategy used by the connection running the transaction to prevent concurrency problems when multiple transactions access the same data.

Specifying Isolation Levels of a Transaction



Session 10

The following table describes the concurrency errors that can occur if multiple transactions access the same data at the same time.

Concurrency Error Description

Dirty read A transaction reads the data that has not been committed by the other transaction. This can create problem if a transaction that has added the data is rolled back.

Nonrepeatable read A transaction reads the same row more than once and a different transaction modifies the row between the reads.

Phantom read A transaction reads a rowset more than once and a different transaction inserts or deletes rows between the first transaction’s reads.

Specifying Isolation Levels of a Transaction (Contd.)



Session 10

The various types of isolation levels of a transaction are:Read Uncommitted

Read Committed with Locks

Read Committed with Snapshots

Repeatable Read

Snapshot

Serializable




Session 10

The following table describes the various isolation levels and the corresponding concurrency errors for a transaction.

Isolation Level Dirty Read Nonrepeatable Read Phantom Read

Read Uncommitted Yes Yes Yes


No Yes Yes


No Yes Yes

Repeatable Read No No Yes

Snapshot No No No

Serializable No No No




Session 10

Let us understand how to set the isolation level of a transaction to Read Committed.TransactionOptions options = new TransactionOptions();

options.IsolationLevel =System.Transactions.IsolationLevel.ReadC ommitted;

using(TransactionScope ts = new TransactionScope(TransactionScopeOption.Required, options)){

using (SqlConnection cn = newSqlConnection("Initial Catalog=HR;Data Source=SQLSERVER01;User id=sa;Password=niit#1234;")){

cn.Open();

Initializing the TransactionOptions object

Setting the Isolation level of both transactions to Read Committed

Creating a connection to a data source




Session 10

using(SqlCommand cmd = new SqlCommand("INSERT INTO Department(cDepartmentCode ,vDepartmentName,vDepartmentHead,vLocation) VALUES(2013,'IT','Lara King','Houston')", cn)){

int rowsUpdated = cmd.ExecuteNonQuery();if (rowsUpdated > 0){

Creating a SqlCommand object to insert a record in the Department table




Session 10

using (SqlConnection cn1 = new SqlConnection("Initial Catalog=HR;Data Source=SQLSERVER01;User id=sa;Password=niit#1234"))

{

cn1.Open();

using(SqlCommand cmd = new SqlCommand("INSERT INTO HRusers(cUserName,cPassword) VALUES('Hansel','Lord')", cn1))

Creating another connection to the same data source

Creating another command object to insert a record in the HRusers table




Session 10

Calling the Complete() method to commit both transactions


{

int rowsUpdated1 = cmd1.ExecuteNonQuery();

if (rowsUpdated1 > 0)

{

ts.Complete();

}}}}



Session 10

Which isolation level supports the occurrence of Dirty read, Nonrepeatable read, and Phantom read?1. Read Committed with Locks

2. Serializable

3. Read Committed with Snapshots

4. Read Uncommitted

Just a minute

Answer:4. Read Uncommitted



Session 10

Problem Statement:Pamela Cruz has joined as an HR executive in Tebisco. Therefore, her details that includes user name and password needs to be inserted in the HRusers table. In addition, the details about her position needs to be added in the Position table. Both the operations need to be performed simultaneously in both the tables. As a part of the development team, you need to add the required details for Pamela in the HR database.

Note: To enable execution of the distributed transactions, you need to ensure that the MSDTC services are running on your system.

Demo: Managing Distributed Transactions



Session 10

In this session, you learned that:A transaction is a logical unit of work that must be completed to maintain the consistency and integrity of a database.

A transaction has the following properties:Atomicity

Consistency

Isolation

Durability

The two types of transaction are:Local transactions

Distributed transactions

Summary



Session 10

A local transaction performs on a single data source. The IDbTransaction interface contains methods for creating and performing local transactions against a data source.

A distributed transaction performs on multiple data sources. A distributed transaction enables you to incorporate several distinct transactional operations into an atomic unit that either succeed or fail completely.

Bulk copy operations can be performed as an isolated operations or as a part of a transaction. By default, a bulk copy operation is its own transaction.

An isolation level determines the effect a transaction has on other transactions that are currently running, and vice versa.

Summary (Contd.)



Session 10

The various concurrency errors that can occur when multiple transactions access the same data at the same time are:

Dirty read

Nonrepeatable read

Phantom read

The various types of isolation levels are for a transaction are:Read Uncommitted



Repeatable Read

Snapshot

Serializable

Summary (Contd.)

Technology

Ado.net session10