A little background:
I've designed my interfaces, which are used by clients, to be as
standalone as possible. Therefore Qi4j is quite invisible there. If a
client doesn't or can't use Qi4j, it can say
VanillaContext context = VanillaContextProvider.createNewContext();
SomeThing thingie = context.getSomeFactory().createSomeNewThing();
Here creating context does all the Qi4j application assembling, etc,
behind the scenes.
Now, when SomeThing is an Entity, currently problems arise with
UnitOfWork. From what I understand, now client must have UnitOfWork
opened whenever it wants to touch thingie? (OK that sounds a little
wrong. :) )
BUT, our client didn't want or couldn't use Qi4j at all! So there must
be some way to create new UnitOfWork behind the scenes whenever
required. Most appropriate situation for that would be whenever
entering entity's method and no UnitOfWork is available. I tried
UnitOfWorkPropagation, but that seems to be suitable only when
handling entities within tagged methods.
I could do
public interface SomeThingWrapper extends SomeThing, TransientComposite
{
// mostly call-through methods to entity
}
However, that is not very convient. Additionally, it is problematic
when SomeThing is given to some other place as parameter, and the code
has to figure out whether the parameter is wrapper or real entity, and
if wrapper, how to get hands on real entity? Some kind of mapping
maybe? It gets too complicated and too much work IMO.
Now, what really would be great, is that when creating VanillaContext,
I could use contextual fragments to add generic concern to all
entities. These concerns would create UnitOfWork whenever needed prior
actually entering the method. IE same as UnitOfWorkPropagation, but it
would affect on ALL methods of SomeThing.
That is currently not possible, as UnitOfWorkException is thrown
almost immediately after going through constraints, if UnitOfWork is
not open. Question is, is there some specific reason behind this?
Could it be better policy to check for UnitOfWork only when it is
really needed, ie when property, association, or maybe private mixin
is accessed within concern? And of course right after concerns, if
none of the concerns accessed entity's state in any way.
Assuming that UnitOfWork MUST ALWAYS be opened whenever even thinking
about accessing concerns of Entities, one could use constraints. Then
one would need to create a constraint, which would check some value to
see if vanilla context is being used, and if so, would create new
UnitOfWork whenever needed. For doing this, currently I would need to
add at least one tagged parameter in every method of every entity then
- dirty hack. :) In this situation those method-constraints me and
Rickard discussed earlier would become handy - I would still need to
tag every method though, which is error-prone and dull.
Of course, if there is some other simple solution to my problem, I
very much would like to hear it. :)
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