ROW LOCK IN SQL SERVER 2005

Question

Please someone explain me how to lock exact row for UPDATE and DELETE. from my java application. I am testing with sql jdbc 2.0. I want in my application prevent simultaneous editing of the same record.

Answer 1

I think the term you are interested would be:
optimistic concurrency java
google that for some ideas.
Here is the rundown on one approach to it:
Most people read data and dont update too often.
When they update, they usually update separate records.
Therefore your approach is to be optimistic in assuming records are not altered while the end user
is looking at it (however, still handle the few times it happens).
A bad design is to display 100 records and when the user changes one of them, update all 100.
Doing that means you will almost always have changed data.
The correct way is to only update the changed record.
One solution is this:
For each database table, add a new column called 'version'. that you increment by one every time the record is updated. When you call up the record to display to the end user, you make note of the version number. You let him alter the record. When he goes to update, you compare the version number you made note of with the one in currently in the database. If it changes, you alert the user the data has changed. Then you may show him what changed and does he want to overwrite it. Usually, the situation seldom occurs (optimistic).
You need to check the version and update atomically (in a transaction for example). Here is a way to do it atomically (ie, in one sql statement instead of two):
update person set firsName='John' where personID=? and version=?
For delete, just go ahead and delete the record, the .executeUpdate() statement returns the number of records deleted. If its zero, you know someone previously deleted it. Similarly, if you go to update a record that someone prevously deleted while you were looking at the record, the update will return a value of zero instead of one.