[jboss-user] [JBoss Seam] - Re: Layering the code in Seam

[Grandfatha]

If you create the EntityManager in the presentation layer and pass it down to the DAO layer, then I dont see no difference to invoking the method of EntityManager right inside you presentation bean.


Truely layered code would mean that you business code would not even know about an Entity Manager let alone your presentation code. Truely layered means, that the presentation bean calls a business method and gets a result and does not care about how this result is produced. 


In my view, only the DAO class should have a dependency to the EntityManager IF you want to truely structure your code into independent layers. Thats great for maintenance and testing since each layer can swapped out or replaced by a different implementation without breaking  e.g. the layers above. 


But this flexibility in the long term is bought by a higher complexity and more code in the short term. Maybe you will even have to deal with "LazyInitializationException" again depending on how you work with the Entitymanager/Seam components.

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