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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