What different transaction isolation levels provided in WCF?

 Posted by articlesMaint on 9/14/2009 | Category: WCF Interview questions | Views: 36979

Transactions assure that a group of related activity occurs as a single atomic unit. In simple words, every activity in the unit must either all succeed or all should fail. WCF provides a central transaction system that can be used to handle transaction operations. One of the things WCF provides is a single unified transaction system for both database and non-database activity. For instance, BeginTrans and CommitTrans are database related syntaxes but we can not use the same for other activities like if we want to upload all message in a single transaction to a MSMQ server. One thing to note is that WCF transaction abides to WS specifications. That means any other language like JAVA can take advantage of this transaction…. I think that is the best part of WCF embracing other languages.

Figure 26:- Transactions in WCF

In order to support transaction the service should first support transactions. Above is a simple code snippet of the server service and client and explanation for the same:-

The top code snippet is of the server service and the below code snippet is of the client.

1 - At interface level the operation contract is attributed with [Transaction Flow] attribute. There are three values for it Allowed (which mean operation mar or may not be used in transaction), Not Allowed (Where it is never used in transaction) and required (Where the service can only be used in transactions). Below code snippet currently says that this service can only be used with transactions.

2 - In this section the [Service Behavior] attribute specifies the transaction isolation level property. Transaction isolation specifies the degree of isolation most compatible with other applications. So let us review what are the different levels you can provide in transaction isolation.
The data affected by a transaction is called volatile.
Chaos: - pending changes from more highly isolated transactions cannot be overridden.
Read Committed: - Volatile data can be modified but it cannot be read during the transaction.
Read Uncommitted: - Volatile data can be read as well as modified during the transaction.
Repeatable Read: - Volatile data can be read but not modified during the transaction and new data can be added.
Serializable: - Volatile data can be only read. However, no modifications and adding of new data is allowed.
Snapshot: - Volatile data can be read. However, before modifying the data it verifies if any other transaction had changed data. If yes then it raises error.
By default, the System. Transactions infrastructure creates Serializable transactions.

3 - This defines the transaction behavior with in the service. [Operation Behavior] has a property called as transaction scope. Transaction Scope setting indicates that operation must be called within a transaction scope. You can also see TransactionAutoComplete is set to true which indicates that transaction will complete by default if there are no errors. If you do not provide the TransactionAutoComplete to true then you will need to call OperationContext.Current.SetTransactionComplete() to make the transaction complete.
Now let us make a walkthrough of the client side code for the service.

4 and 5 - You can see from the client we need to define Isolation level and the scope while making the call to our Update Accounts method

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