[cdi-dev] CDI + transactions query

[Pete Muir]

On 22 Aug 2012, at 15:29, Tom Jenkinson wrote:

> Hi Pete,
> 
> Would it make sense to maintain the same restrictions as JMS?
> 
> In JMS you can initiate a new transaction from onMessage, analogous to a method decorated with @Observes. If the method returns without completing the transaction then an error is logged and the transaction rolled back.
> 
> Flowing a transaction from an event producer to an event consumer isn't a great idea (it doesn't work in JMS either). But allowing a consumer to control their own transaction does seem to make sense to me.

Yes, that makes sense.

> 
> Admittedly this is a gut reaction, I read through the Jira and the doc you linked to though, and used my JEE experience to draw analogies, do let me know if I got the wrong end of the stick please!

No, I think this is right.

In that case, what I would suggest we do is:

* explicitly make controlling transactions from observers non-portable (which allows implementors to experiment with such a feature without breaking spec compliance)
* raise a feature request in CDI to consider adding something like what you describe in the future

> Tom
> 
> On 2012-08-22T13:20:52 BST, Pete Muir wrote:
>> Hi Paul, Tom, Mike,
>> 
>> I have an open issue in CDI - https://issues.jboss.org/browse/CDI-213 - which I would like your input on.
>> 
>> Events in CDI are very simple (you can read more at http://docs.jboss.org/weld/reference/latest/en-US/html/events.html) and provide a typesafe implementation of the observer/observable pattern. Currently the spec prohibits manipulating transactions from an observer method, but it doesn't say what happens if someone does try to do this [1].
>> 
>> So, what I'm asking is really whether it really makes no sense to allow this, or whether it's best to say that it's "non-portable", which means that an implemenation might offer this as a feature above and beyond the spec. Furthermore, it may be that it's not really possible to disallow this, in which case we would need to go with non-portable as well.
>> 
>> Thanks
>> 
>> Pete
>> 
>> [1] If we say that it leads to an exception, we can then check it in the TCK, which is good :-)