I can't help but think "DomainObject" is a far better representation of the
(Business) Problem Domain concept than "DomainEntity".
DDD for some reason known only to Eric Evans made a fetish of the term "Domain
Entity" as a type of "Domain Object". It was defined in juxtaposition to a
contrived "Value Object" type Domain Object. Sure some domain objects are light
on "Identity" but that doesn't imply such domain objects always lack
significant behaviour or attributes (I'm thinking of Coad's "Description"
archetypes here).
"Entity" has unfortunate connotations - anemic domain model antipattern, EJB
1&2, ...
So what is wrong with just plain old "Domain Object"?
On Wednesday, 31 December 2014 10:05 PM, David Tildesley
<[email protected]> wrote:
Hi Dan,
Perhaps a prefix that is layer agnostic for those annotations?
Regards,David.
On Wednesday, 31 December 2014 7:42 PM, Dan Haywood
<[email protected]> wrote:
On 30 December 2014 at 23:44, David Tildesley <[email protected]> wrote:
> +1 for the counter proposal (although I would suggest cloning/deriving
> "@DomainObjectLayout" to "@ViewModelLayout" etc. so that "Domain*" tags are
> not used in ViewModel - less confusing).
>
>
On a different thread to dev@ I also made a related proposal that
@Property, @Collection, @Action etc be renamed to @DomainProperty,
@DomainCollection, @DomainAction etc... the primary reason being that
clashes with @Collection clashes with java.util.Collection, plus I like the
idea of all Isis-related annotations starting with an @DomainXxx prefix.
No one's commented on that, yet.
Given your preference of @ViewModel and reserving "@Domain" to be strictly
for domain layer concepts, would I be right to guess you wouldn't be in
favour of adding "Domain" as a prefix to all those annotations?
> On Tuesday, 30 December 2014 3:07 AM, Dan Haywood <
> [email protected]> wrote:
>
>
> On 29 December 2014 at 13:23, GESCONSULTOR - Óscar Bou <
> [email protected]> wrote:
>
> > Ok.
> >
> > So let's raise some questions/doubts :)
> >
> > *** @DomainObject ***
> >
> > Is a ViewModel a DomainObject at all ?
> >
> >
> it's a good question, and I've debated it myself. Let me lay out my
> thinking on this so far and see if we can collectively come to a view on
> this.
>
> First thing to note is that there are two "varieties" of view models (even
> though the implementation is identical)
>
> - those that are part of the domain layer and are, conceptually at least,
> entities, but where the persistence is managed outside of Isis. An example
> is a document in a CMS
> - those that are part of the application layer, and represent a view on top
> of one or more entities.
>
> Of course, we expect an application layer to depend on the domain layer and
> not vice versa, but even so, because some view models are conceptually
> entities I suspect that in a typical Isis application it will be reasonable
> to allow JDO-managed domain entities to interact with externally-managed
> view model entities.
>
>
> Because of this, I've been thinking of "DomainObject" as being a superset
> of both entities and view models.
>
>
>
>
> > I would consider them as a different kind, so the @ViewModel annotation
> > shouldn't be deleted.
> >
>
> You are certainly right that quite a few of the features in @DomainObject
> don't apply to view models (even if conceptually they are entities)...
> because we rely on JDO to implement. Specifically:
>
> - auditing... requires JDO so doesn't apply to view models
> - publishing ... requires JDO so doesn't apply to view models
> - bounded = not sure... even though doesn't depend on JDO, suspect that it
> isn't supported for view models
>
> - autoComplete ... is supported for view models
> - editing ... is supported so long as the ViewModel.Cloneable interface is
> also implemented. I can foresee this restriction being lifted in the
> future
> - objectType ... is supported for view models (used as REST URLs)
>
>
>
>
>
> > Also, perhaps we can introduce Isis platform logic like not
> > "saving/persisting" view models, etc. If that would be the case, the
> > "editing" and "editingDisabledReason" at least might not have any sense.
> >
> >
> Not sure I understand this point. But at any rate, given that some view
> models are basically externally-managed entities, the semantics of
> "saving/persisting" would also apply.
>
>
>
>
>
> >
> > If so, I would better align with DDD naming conventions, in order to gain
> > acceptance.
> >
> > So, names should be @Entity or @DomainEntity (for avoiding name collision
> > with JPA) - instead of @DomainObject -.
> >
> >
> I did consider @DomainEntity, but as I say, sometimes view models act like
> entities. I do quite like it though.
>
> I have a counter-proposal, see below.
>
>
>
> > I like the @DomainService name, as it can act as a DDD Factory and/or
> > Repository.
> >
> >
> > As currently there's no "special" support for AggregateRoots or
> > ValueObjects, no more annotations are needed.
> >
> >
> Sounds like a vote to deprecate. Jeroen has said the same thing. Perhaps
> they should be deleted in v2.0 and reappear, if we want them back, in v3.0.
>
>
>
> > So the proposed set would be:
> > • @ViewModel and @ViewModelLayout
> > • @DomainService and @DomainServiceLayout
> > • @DomainEntity and @DomainEntityLayout
> > • @Property and @PropertyLayout
> > • @Collection and @CollectionLayout
> > • @Action and @ActionLayout
> > • @Parameter and @ParameterLayout
> >
> >
> >
> Here's my counter-proposal. It's not as symmetrical as before, but perhaps
> is less confusing overall:
>
> * replace @DomainObject(viewModel=false) with
> @DomainEntity(persistence=JDO)
> ... this would be the default
> * replace @DomainObject(viewModel=true) with
> @DomainEntity(persistence=EXTERNAL)
> ... for view models representing externally-persisted entities. In the
> Javadoc, say that auditing, publishing and bounded are not supported for
> these
> * keep @ViewModel
> ... extend to include the non-entity stuff from @DomainObject that does
> apply (basically, I think that's just "objectType" )
> ... the intention being that this is used for application-layer views.
>
> keep @DomainObjectLayout, because everything in it applies equally to both
> view models (either variety) and JDO entities.
>
>
> I'll reply on your points on @Property and @Parameter separately.
>
> Thx
> Dan
>
>
> >
>
>
>
