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From Alasdair Nottingham <>
Subject Re: jpa blueprint ns handler question
Date Fri, 05 Nov 2010 21:05:37 GMT


On 5 Nov 2010, at 20:16, Jarek Gawor <> wrote:

> On Fri, Nov 5, 2010 at 6:08 AM, Timothy Ward <> wrote:
>> To clarify, the aim when designing this function was to make consuming persistence
units and contexts as simple as possible - hence trying to make sure that it could be expressed
as a single element.
>> The primary injection mechanism people use is by setters, which in blueprint would
be something like:
>> <property name="foo" ref="bar"/>
>> In order to get JPA to be similarly concise, and to avoid breaking the existing validation
requirements of Blueprint, we came up with the <unit/> and <context/> tags, which
contain the information from an @PersistenceContext and @PersistenceUnit annotation.
>> The decision was made that:
>> <property name="emf" type="javax.persistence.EntityManagerFactory">
>>   <jpa:unit unitname="myUnit"/>
>> </property>
>> was significantly less usable than:
>> <jpa:unit property="emf" unitname="myUnit"/>
> I disagree. To me the following is much clearer:
> <property name="emf">
>  <jpa:unit unitname="myUnit">
> </property>
> And this syntax is consistent with rest of the blueprint syntax, i.e.
> how you would inject a bean as a property or argument. The <jpa:unit/>
> and <jpa:context/> provide a specific object just like a <bean/> or
> <reference/>, etc. and should be handled in the same way, IMHO.

It depends on what you consider jpa:context is doing. I you think it defines a bean that is
an entity manager then I understand your point, if you consider it the equivalent of @PersistenceContext
then I think the scheme as is makes sense.

My view has always been that it is the equivalent of the @PersistenceContext annotation, so
I like the scheme as is, and it makes sense and is clear.


> Jarek

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