How to lock the rows in a transaction so others cant modify the rows

Hi,
I want few suggestion in the following scenario .
I have a few records ( say 100 ) in a table which Im sending to the client over a network and are populated in a swing GUI...Now the client selects few of them ( say 3 ) and submits to the server. Now the server should assign a number to those rows and store them in the database. As it is a multi client environment While assigning the number it should check that no other client has already assigned a number to at lease to one of the row in the meantime. in that case it shoudl fail.
In this case i want to lock those 3 records when the request arrives at the server assign number commit and release the lock.
I want to avoid deadlocks.
Can any one suggest me whoch locking policy should i use and how ?
Thanx in advance...
Mahi

It depends on how acceptable it is for your commit to fail. By far the easiest and safest thing to do is use Optimistic Locking. This way if the server tries to commit changes to something that has already been committed, an Optmistic Lock exception will be thrown. It's up to your application to handle this, and depending on your domain and the likelyhood of this happeneing, you could just tell the user "try again". The other option is pessemistic locking, which is very, very, dangerous (in my opinion). The main issue is that it's resource intensive, and different databases have different semantics on how it works.
IIWY, I'd look at Optimistic Locking in the docs and go from there.
- Don

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---
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 Oracle TopLink, EclipseLink
 Wiki: Java Persistence, EclipseLink

How to lock the rows in a transaction so others cant modify the rows

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