Concurrency Issue : J2ee Application

Question

Hi,
Ours is a J2ee Web Application, Where in we have maintenance screens (for doing CRUD(Create-Read-Update-Delete) operations) for each entity. Each entity has a business key which identifies that entity uniquely. So, from the Create screen, if I try to create a record with the same business key, it should say Object already exists. So, before we create a record, first we search for it using the business key. If we get any results for the search criteria, we will say, Object already exists else we will create the record.
Now the problem is, When we try to create two records with the same business key from two different screens. We open two browsers, and create a record with the same business key from two screens. Both the records are getting created. As per our analysis, What happens is, the search operation in both the screens is being done simultaneously, so, both the search operations does not return any result because of which both the records are getting created. If the record is created between the both search operations, then one thread sees the created record and says object already exists.
It would be of great help if you can give us the pointers in solving this concurrency issue. We are using EJB's in our project. Does changing the Isolation Level of the create and search methods help us?
Thanks & Regards,
Yong-Loh

Answer 1

search for the record right before you try to insert a new one; if another user inserted one while the user was busy typing, you'll catch it then. If you want to prevent 100% of the time that you don't get duplicate entries because of the rare occurrence that two people insert the exact same data at exactly the same time, figure out which fields uniquely identify a record (besides the ID) and put a unique constraint on them.
Note: that whole story was far from a clear description or question; you may want to narrow it down to a more compact description if I my answer doesn't help you.