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From Markku Saarela <>
Subject Re: How to determine in which container code is running?
Date Mon, 31 Dec 2012 17:40:45 GMT
JPA is one implementation of DataMapper.

One idea of Domain Model with UOW is that it decouples persistence layer 
from domain implementation and tracking changes of the domain objects.

Domain Model does not know anything about persistence. When domain 
object is created or otherway manipulated it register that it's state 
has changed to the UOW instance and when user or service decide to save 
state of the domain objects they call UOW method commit() which delegate 
work to actual persistence implementation(JPA for example).

So these patterns are not reinventing the wheel again (persistence), 
instead it describe how to build  effective software with domain model 
that is totally independent of EIS layer.



On 12/31/2012 06:55 PM, David Jencks wrote:
> I'm not familiar with this particular way of describing UOW or data mapper, but you might
consider whether they are irrelevant with ee facilities.  The whole purpose of EJBs is to
provide declarative transaction management, which is what UOW usually means.  A tiny bit of
googling of data mapper makes me ask why you wouldn't use jpa.  I haven't read Fowler's books
for many years, I thought his refactoring book was really good, but the design patterns ones
seemed to me to be reinventing the wheel as far as ee goes.
> thanks
> david jencks
> On Dec 31, 2012, at 8:18 AM, Markku Saarela wrote:
>> My use case is to implement Martin Fowler's Domain Model enterprise design pattern
with Unit Of Work and  Data Mapper.
>> This UOW does not work with ThreadLocal in every app server due to thread pooling.
>> So only solution to use different UOW storing mechanism in different layers;
>> session persistence in web container and pass UOW instance to the EJB container and
store it to TransactionSynchronizationRegistry. Of course standalone Java client could use
TrhreadLocal implementation.
>> In UOW static methods to manipulate current UOW instance (getCurrent(), newCurrent()
etc,) must some how decide which implementation to use.
>> Markku
>> On 12/31/2012 06:06 PM, David Jencks wrote:
>>> On Dec 31, 2012, at 7:57 AM, Markku Saarela wrote:
>>>> Hi,
>>>> Has Java EE spec any API to determine is code running in EJB or WEB container?
>>> no.
>>>> Or is there any better way than examine stacktrace?
>>> I'm imagining that you have some library or perhaps CDI code that is called from
both a servlet and an ejb?  Why do you care?  Just to figure out why something is working
the way it is, or do you need to take different action depending on what calls this code?
 You could pass appropriate context information to the code in question from the caller.
>>> david jencks
>>>> Rgds,
>>>> Markku

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