Why is transaction processing very important for web applications?

31. Why is transaction processing very important for web applications?

Transaction processing is very important for Web applications that use data access, because Web applications are distributed among many different clients. In a Web application, databases are a shared resource, and having many different clients distributed over a wide area can present the below key problems. Contention for resources: Several clients might try to change the same record at the same time. This problem gets worse the more clients you have. Unexpected failures: The Internet is not the most reliable network around, even if your Web application and Web server are 100 percent reliable. Clients can be unexpectedly disconnected by their service providers, by their modems, or by power failures. Web application life cycle: Web applications don’t follow the same life cycle as Windows applications—Web forms live for only an instant, and a client can leave your application at any point by simply typing a new address in his or her browser.

32. List the steps in order to process a transaction?

1. Begin a transaction.

2. Process database commands.

3. Check for errors.

4. If errors occurred, restore the database to its state at the beginning of the transaction. If no errors occurred, commit the transaction to the database.

33. Explain how a DataSet provides transaction processing?

DataSet provide transaction processing through the RejectChanges and Update methods. DataSet also provide an AcceptChanges method that resets the state of records in a data set to Unchanged. Data sets provide implicit transaction processing, because changes to a data set are not made in the database until you invoke the Update method on the data adapter object. This lets you perform a set of commands on the data and then choose a point at which to make the changes permanent in the database.

 If an error occurs during the Update method, none of the changes from the data set is made in the database. At that point, you can either attempt to correct the error and try the Update method again or undo the changes pending in the data set using the data set’s RejectChanges method.

34. Give an example to show how DataSets provide transaction processing?

Let us assume we have a DataGrid that displays employee information. Every row also has a delete button, which when you click will delete that row. On this page we also have a Restore and Commit buttons. When you click the Restore button you should be able to restore the data to its previous state. When you click the Commit button you should be able to update the database with the deletions made in the DataSet.

35. What are the 3 types of transaction objects available in ADO.NET?

As we have 3 types of database connections in ADO.NET, there are also 3 types of transaction objects:

1.     SqlTransaction

2.     OracleTransaction

3.     OleDbTransaction

36. What are the steps involved in using a transaction object in ADO.NET?

1. Open a database connection.

2. Create the transaction object using the database connection object’s Begin Transaction method.

3. Create command objects to track with this transaction, assigning the Transaction property of each command object to the name of the transaction object created in step 2.

4. Execute the commands. Because the purpose of transaction processing is to detect and correct errors before data is written to the database, this is usually done as part of an error-handling structure.

5. Commit the changes to the database or restore the database state, depending on the success of the commands. Close the database connection.

37. What property of a transaction object determines how concurrent changes to a database are handled?

IsolationLevel property of the transaction object is used to determine how concurrent changes to a database are handled.

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