Re: Created DDD Exampe - Feedback?

Also having read through everything.

Your method should probably be move on the aggregate not moved (you are
telling the aggregate to do it the event would be moved)

There seems to be a lot of confusion with the usage of an "event store".
You are really just using a message queue (unless I missed where you
refactored to event sourcing).


In this scenario, the transaction boundaries are at the ApplicationService.
We can argue that the JMSMessageReceiver might call the CustomerService,
and do it around a JMSTransaction. This is also a viable solution.


Along the same lines it seems you have introduced a rather large problem
(though subtle) when introducing the domain event. You now need a
transaction between you backing model and the message queue/event store
that you introduced.

The tricky part is Event de-duplication. This can happen in case of
infrastructure failure or system outage. This can be avoided by giving
every Event an unique id, and track which ids were already processed.

Another tricky part is Event ordering. This depends on the messaging
infrastructure. If the infrastructure supports Event ordering, everything
is alright. If not, this must be implemented by ourselves. In any case it
is a good practice to design Events as an idempotent operation. This means
that every Event can be processed multiple times, and every time with the
same result without unwanted side effects.

These are actually pretty easy if done right. You can easily simulate
transactional messaging over an at least once path. Generally you do not
however want to hold every message id (imagine you get 100k/second).
Instead a stream is a sequence treat it that way. Transactionally save your
checkpoint (last completed message) with your processing. This will
simulate transactional messaging. You can see this in practice in the
durable subscriber in clientapi in the dev branch of
github.com/eventstore/eventstore



Cheers,

Greg

On Saturday, May 11, 2013, Greg Young wrote:

> It's also got a great example of words in different contexts. "body
> leasing domain" when I read that I thought it was a joke for a moment ;)
>
> On Saturday, May 11, 2013, mirko.sertic wrote:
>
> **
>
>
> Hi@all
>
> I really like the idea of domain-driven design. Based on a project I am
> working on at the moment I created a small example about what can happen to
> application architecture if strategical and tactical patterns are applied
> to the problem space.
>
> This example can be seen here:
>
> http://www.mirkosertic.de/doku.php/architecturedesign/dddexample
>
> It is far from being perfect, but it should show up a direction about how
> to find subdomains, bounded contexts, aggregates, context integration and
> application architecture.
>
> Any feedback is very welcome, so stay tuned and happy DDDing:-)
>
> Regards
> Mirko
>
>  
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Le doute n'est pas une condition agréable, mais la certitude est absurde.