How to build a domain model with JPA2 and Hibernate

I have been working with enterprise system for a while and mainly as an Infrastructure Architect – The person that binds all things together to a complete working system. One of the many integrations in an enterprise system, is the internal integration from the code (domain model) to the database. This is normally called ORM (http://en.wikipedia.org/wiki/Object-relational_mapping) – Object-relational mapping. Over the many years I have worked with this, the integration of cause have evolved from a simple and direct SQL approach to gigantic automatic frameworks. This is of cause both a good and a bad thing.

This first question I normally get when talking about ORM is: What about the overhead – is it fast enough? And the simple answer is…. NO!
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