Tuesday, November 29, 2011

ADO.NET interview questions: - Elaborate different implementing ways of optimistic locking in ADO.NET.

This is one of the ADO.NET interview questions asked in the interview. Answer this question with the simple steps as follows.

Ways to implement optimistic locking using ADO.NET: -
  • When we call “Update” method of Data Adapter it handles locking internally. If the Dataset values are not matching with current data in Database, it raises concurrency exception error. We can easily trap this error using Try. Catch block and raise appropriate error message to the user.
  • Define a Date time stamp field in the table. When actually you are firing the UPDATE SQL statements, compare the current timestamp with one existing in the database. Below is a sample SQL which checks for timestamp before updating and any mismatch in timestamp it will not update the records. This I the best practice used by industries for locking.
Update table1 set field1=@test where Last Timestamp=@Current Timestamp
  • Check for original values stored in SQL SERVER and actual changed values. In stored procedure check before updating that the old data is same as the current Example in the below shown SQL before updating field1 we check that is the old field1 value same. If not then some one else has updated and necessary action has to be taken.
Update table1 set field1=@test where field1 = @oldfield1value

Locking can be handled at ADO.NET side or at SQL SERVER side i.e. in stored procedures: -

Also see the following video on Table Scan And Unique key in SQL Server: -

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1 comment:

jaylen watkins said...

How to trap the error and other question may be asked during this kind of interview so get prepared to
Interview Questions