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While doing a spot check on code and configuration – I noticed that the developer wasn’t throwing a runtime exception nor was he setting rollbackOnly in a CMT EJB. I was told that any exception will rollback a transaction and it is not possible to setRollbackOnly, and there are only 4 types of transaction attributes on CMT. Wrong, wrong and wrong. 1. If your code throws an application exception – the container expects the bean to handle it. However, if your bean throws a runtime exception (or subclass), like javax.ejb.Exception – the container will rollback the transaction. 2. If you don’t want to throw RTEs all around your code – and/or you have massive catch all exception code blocks, you should context.setRollbackOnly – to rollback transactions. 3. There are various transaction attributes – 6 to be exact: Requires, Requires New, Supports, Not Supported, Never & Mandatory. Never and Mandatory are opposite to one another. Requires starts a transaction if not called with one, M...

I’ve always done ORM with HIbernate –and it helped a lot with cardinality (besides ORM general features). 1:1::Married Couple (there are cultural and religious exceptions) 1:n:: Order: Line Item n:1:: Line Item: Order n:n:: Course: Student Regardless of cardinality, entities should never be non-singular from a naming convention stand point. In Bidirectional relationships – the inverse side must refer to its owning side via the mappedBy element. In n:1, the many side always owns the relationship. In n:n – it doesn’t matter. All in all the beauty of Java Persistence API is that it has all the features that Hibernate had – and then makes things a lot simpler with Annotations. I never was a fan of annotations when they first surfaced, but I have slowly come to like it. I like the encapsulation it provides. You can mix non-entity super classes with entity super classes, use polymorphic associations, queries etc. It is surprisingly flexible. Three basic strategies remained consiste...