Hi Oscar,
Seems to me it's the same thing:
Let me add some clarity to that DDD example you shared:
Port ---> Domain Model <---Adapter
is just a different set of terms for the same layers:
User Interface --> Problem Domain <--- System Interface
Chaining applications together in an integration you get Adapter "A" of AppA
calling Port "B" of AppB and so on - which I am guessing is what you meant by
"Inter Domain".
Clearly ViewModel fits into "Port" quite nicely. In fact it's the only place
it belongs.
But "Intra Domain"? Does ISIS in some way prevent a domain object calling
another domain object's operation directly? Anyway I suspect that's a separate
discussion.
The bottom line is that we can't stop people bleeding domain model behaviour
out into viewmodels, however what we can do is to make it as clear and
unambiguous as possible by avoiding/reducing overloading of terms/concepts and
suggesting the correct approach to building an application.
My single piece of advice to folk: If you want to avoid a disaster then make
sure you model your problem domain in a "just enough" consensus modelling
exercise before your team goes anywhere near "View Models" or any other part of
the UI layer. ISIS offers nothing new that would change this advice.
However "View Models" could be the scaffolding that you end up hanging yourself
and your team on if you don't understand that they are not part of your domain
model.
I guess I should shut up now as I am just repeating myself.
In summary: Big Tick for the addition of: "@DomainObject (External)" so that
we don't have to misuse "@ViewModel"
Regards,David.
On Saturday, 3 January 2015 10:24 PM, GESCONSULTOR
<o....@gesconsultor.com> wrote:
Hi David!
What it's clear is that properties/collections can be useful not only for
domain layer objects, so the @Domain prefix should not be added.
Regarding the Application Layer, I agree that sometimes it can be a clear
indication of an anemic domain. But properly implemented and used, it's well
accepted on the DDD community as a way to create a layer over domain entities
for orchestrating them. They're useful for representing Domain Entities the way
is most useful for the end-user as perhaps the Domain Entities have been
designed from another perpective different from that concrete use case.
There are some examples on the latest book, "Implementing DDD" by Caughn Vernon.
That use case is really similar to the most common use in Apache ISIS, with the
advantage that the UI is automatically generated from it
Anyway I don't advocate for using ViewModels only for the Application Layer,
but in all case where "views" can be useful, including intra-domain or
inter-domain use cases (for example, for modeling the integration patterns
described on the "Implementing DDD" book such as Ports and Adapters.
as an example sure you will find interesting this sole implementation made by
Vernon, and how they could be implementing by Apache Isis[1].
So yes, as you said we must be careful with anemic domains :))
Regards,
Oscar
[1]
https://github.com/VaughnVernon/IDDD_Samples/tree/master/iddd_collaboration/src/main/java/com/saasovation/collaboration
> El 1/1/2015, a las 20:45, David Tildesley <davo...@yahoo.co.nz> escribió:
>
> Hi Oscar,
>
> I think we may be looking at the "tail wagging the dog" in this part of the
> thread. I.e. the reason why Jeroen has found ViewModels for some of the
> scenarios he outlined (e.g. "External Entity service" integration) so useful
> was because there was no alternative available to him. This is where Option 1
> tidies things up from a conceptual layer point of view, as discussed earlier
> in the post, but doesn't in any way prevent you from doing what you suggest
> below if that is what you believe is correct i.e. there would nothing forcing
> you to use "@ DomainObject (External)" - you could instead carry on using
> "@ViewModel" within your domain layer if that is what you think is correct.
> For those of us that believe this is conceptually wrong, Option 1 keeps us
> happy because now we have "@ DomainObject (External)" available to us and
> furthermore, it allows "@DomainObject (External)" to evolve independently of
> "@ViewModel" sometime in the future.
>
> i.e. Option 1 removes the layer overloading as Dan already points out.
>
> On a further note, I don't like to use the concept "Application Layer" - this
> layer was invented by those that ran into difficulty when forced to use EJB 1
> & 2 and unfortunately persisted even when the POJO movement started (maybe
> because it was easier to migrate from the EJB 1 & 2 legacy). I.e the presence
> of an "Application Layer" concept is a very strong indicator of the presence
> of "Anemic Domain Model" anti-pattern [1] and this is pointed out by Martin
> Fowler. Assuming a rich domain model then, what may be thought of as the
> "Application Layer" is really just part of the UI layer.
>
> [1] bliki: AnemicDomainModel
>
>
>
>
>
>
>
>
> bliki: AnemicDomainModel
> If you use an object-oriented domain model, and you don't put behavior in
> your objects, you're missing out on most of the benefits of that pattern.
> View on www.martinfowler.com
> Preview by Yahoo
>
>
>
> Regards,
> David.
>
> On Friday, 2 January 2015 12:40 AM, GESCONSULTOR - Óscar Bou
> <o....@gesconsultor.com> wrote:
>
>
> Hi folks!!
>
> Happy New Year to all those following the Gregorian Calendar !!!
>
>
> As David mentions, we can think about ViewModels to be like "views".
>
> In that case, as Jeroen has commented, those "views" can be useful both at
> the Domain layer and the Application layer.
> So we cannot assume that View Models are going to be useful only for the
> Application layer, but also for the Domain layer.
> And not only they are "views" from this system's domain objects. As he points
> out, Views can also be used to represent external systems entities.
>
> As Isis managed Properties/Collections can belong to any class of this
> Bounded Context / Domain or External Systems Domains objects (being a
> DomainEntity, a ViewModel used on the Domain Layer, a ViewModel used on the
> ApplicationLayer, a ViewModel representing entities managed by External
> Systems) they shouldn't be prefixed with a layer-specific term, IMHO.
>
>
> Oscar
>
>
>
>
>
>> El 31/12/2014, a las 23:40, Branham, Jeremy [HR]
>> <jeremy.d.bran...@sprint.com> escribió:
>>
>> At least it wasn’t DOA =]
>>
>> That helps me understand the evolution of Isis better, and It makes sense
>> the PD would never depend on the UI.
>>
>> So having separate annotations [@ViewModel and @DomainEntity] would help
>> maintain the distinction between UI and PD.
>> Where a single annotation [@DomainObject, @Model, or whatever else] would
>> blur the lines of responsibility.
>> Do I understand this correctly?
>>
>> Jeremy D. Branham
>> Tel: **DOTNET
>>
>>
>> -----Original Message-----
>> From: David Tildesley [mailto:davo...@yahoo.co.nz]
>> Sent: Wednesday, December 31, 2014 4:36 PM
>> To: d...@isis.apache.org; users@isis.apache.org
>> Subject: Re: ISIS-970 ... (new annotations) please review if you get a
>> chance...
>>
>> Sorry - too many new years eve beers - I typed DOI when I meant DI (fuddled
>> with IoC in my brain).
>>
>> On Thursday, 1 January 2015 11:04 AM, David Tildesley
>><davo...@yahoo.co.nz> wrote:
>>
>>
>> Hi Jeremy,
>> The intention of "ViewModel" is provide a Use Case specific mechanism to
>> aggregate/present/"cut and dice" a view of the problem domain. In this
>> respect it is certainly not part of the domain layer and logically belongs
>> the "UI" layer. It was invented as part of ISIS as the mechanism for
>> significantly influencing the UI. In this way, it is a departure from the
>> original concept of Naked Objects from which ISIS evolved, however if you
>> choose not to use ViewModel then you are left with the original concept of
>> Naked Objects and therefore ISIS remains true to Naked Objects.
>> The domain layer has long term enduring value to the business who paid for
>> the application to be built and should never depend on other layers. The
>> "UI" layer should be thought of as "disposable" and will mutate at a high
>> rate, whilst the "domain layer" should remain stable in "shape" and
>> independent of the other layers. There is nothing inherent about ISIS that
>> would give you a valid reason to ignore this architecture pattern. If we
>> ignore the data management layer which is no longer of significance due to
>> persistence frameworks like DataNucleus, JPA, Hibernate, Toplink, etc., then
>> there are only the traditional three layers in consideration for the
>> developer (if they choose not to stick to the pure Naked Objects paradigm
>> for user experience) and the below represents these with the direction of
>> dependency shown by the arrows:
>> UI --> PD <-- SI
>> Where:
>> UI = User Interface (system or human)*PD = Problem DomainSI = System
>> Integration.
>> * UI layer Includes both the ViewModels and the generated UI(s). Where
>> things got messy for ISIS was when Domain Objects in the domain layer were
>> required not to be locally persisted but instead required DOI based
>> integration with an external system (integration). The ISIS Domain Objects
>> were "locked" into local persistance and that was because that was where the
>> initial focus was (necessary because you have to get this right as priority
>> because this is the majority scenario). Then in this vacuum, folk started
>> proposing to use "ViewModel" as Domain Objects that required DOI based
>> external system integration because "ViewModel" was free from the local
>> persistance lock-in. Other proposals were also on the table (e.g roll your
>> own datanucleus persistance plugin) that came with their own headaches.
>> Option 1 then tidies this up and nothing is lost.
>> Speaking to Jereon's point - yes there are some "trivial" system
>> integrations where it is valid to bypass the PD layer and have a direct
>> integration from UI layer to SI layer (e.g fetch a controlled value list
>> from some other system) although I would say that ISIS negates the need to
>> do this anyway by lowering development cost.
>> A step in the right direction is to first sort out the semantics with Option
>> 1 and then later when folk feel comfortable, to have ISIS enforce the UI -->
>> PD dependency direction (i.e. disallow PD --> UI).
>> Applications should reinforce the layer separation via package naming
>> convention. e.g.
>> com.mycompany.myapp.pd.*com.mycompany.myapp.ui.*
>> David.
>>
>> On Thursday, 1 January 2015 3:24 AM, "Branham, Jeremy [HR]"
>><jeremy.d.bran...@sprint.com> wrote:
>>
>>
>> What would it look like with @Model?
>> Giving more specificity than ‘Object’ but opening the interpretation to
>> Entities and ViewModels.
>>
>> Or am I overlooking something? [I am new to Isis]
>>
>> (fyi - there is a name clash with Model in Spring-MVC)
>>
>>
>> Jeremy D. Branham
>> Tel: **DOTNET
>>
>> From: Jeroen van der Wal [mailto:jer...@stromboli.it]
>> Sent: Wednesday, December 31, 2014 7:37 AM
>> To: dev; users
>> Subject: Re: ISIS-970 ... (new annotations) please review if you get a
>> chance...
>>
>> I like this discussion because it's defining where Apache Isis is right now.
>> Personally I think Isis has grown far beyond the concepts of DDD so sticking
>> to it's grammar would limit ourselves.
>>
>> In the applications I'm developing things aren't black or white: we have
>> view models that represent documents in a CMIS document store but in DDD
>> terms they are domain entities. We have view models that are based on
>> entries in a database view but in DDD terms these are domain entities. We
>> have view models that are created on the fly and never get persisted but in
>> DDD terms they are domain entities.
>>
>> As you might expect I opt to simply call everything a domain object.
>> Residing in the application's domain object model. Very easy to explain to
>> newcomers too.
>>
>> Cheers,
>>
>> Jeroen
>>
>>
>> On Wed, Dec 31, 2014 at 1:13 PM, GESCONSULTOR - Óscar Bou
>> <o....@gesconsultor.com<mailto:o....@gesconsultor.com>> wrote:
>> Hi to all.
>>
>>
>> I'm thinking about it but still convinced of option 1 ...
>>
>> In my opinion, annotations are going to be "our main API". So they must be
>> thought from the user's perspective, more than from the implementation's
>> perspective.
>>
>> In that way, aligning with DDD concepts (that are the most widely spread) is
>> more important to me than implementation criteria.
>>
>> So I would keep my vote for implementing:
>>
>> @DomainEntity
>> @ViewModel
>> @DomainEntityLayout
>> @ViewModelLayout
>>
>>
>>
>> Regarding adding the "Domain" preffix to properties and collections, I think
>> it's not needed.
>>
>> As Dan's exposed, they are present on any type of class (despite being a
>> "domain" or "application" level one).
>> As they're annotations an not classes, in my current setup (based on Apache
>> Isis latest snapshot):
>> - @Property does not conflict with any other annotation (i.e., no
>> identically named annotation is present on any dependency).
>> - @Collection does not conflict with any other annotation.
>> - @Action clashes with the javax.xml.ws.Action annotation.
>> - @Parameter clashes with the org.junit.runners.parammetrized.Parameter
>> annotation.
>>
>> None of them can be confused with Isis ones by a junior developer.
>>
>> In fact, this clash conflict was already present with @Named (that it's
>> going to be kept) and same other Apache Isis annotations without being more
>> relevant.
>>
>> So my opinion would be to not add the "Domain" prefix to them.
>>
>>
>> Perhaps this could also be a good moment to add a "collateral" debate :)
>>
>> In my head, I also associate Collections with Properties. I would consider
>> "Simple Properties" and "Collection Properties".
>> So perhaps naming could be instead "SimpleProperty" and "CollectionProperty"
>> ? :-))
>>
>>
>>
>> HTH,
>>
>> Oscar
>>
>>
>>
>>
>>
>>
>> El 31/12/2014, a las 12:39, Vladimir Nišević
>> <vnise...@gmail.com<mailto:vnise...@gmail.com>> escribió:
>>
>>
>> I would vote for most well described DDD terms (described in Evans book) -
>> this would help users to adopt/understand ISIS framework easier and have a
>> kind of reference documentation. Term 'Object' is too general, and "Business
>> Object modelling antipatterns" are also very wide spreaded, e.g. by people
>> like enterpise information modelling architects...
>>
>> Regs, Vladimir
>>
>>
>>
>> Am 31.12.2014 um 07:40 schrieb Dan Haywood
>> <d...@haywood-associates.co.uk<mailto:d...@haywood-associates.co.uk>>:
>>
>>
>> On 30 December 2014 at 23:44, David Tildesley
>> <davo...@yahoo.co.nz<mailto:davo...@yahoo.co.nz>> 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 <
>>d...@haywood-associates.co.uk<mailto:d...@haywood-associates.co.uk>> wrote:
>>
>>
>> On 29 December 2014 at 13:23, GESCONSULTOR - Óscar Bou <
>> o....@gesconsultor.com<mailto:o....@gesconsultor.com>> 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
>>
>>
>>
>>
>>
>>
>> Óscar Bou Bou
>> Responsable de Producto
>> Auditor Jefe de Certificación ISO 27001 en BSI CISA, CRISC, APMG ISO 20000,
>> ITIL-F
>>
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>>
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>>
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>>
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> Óscar Bou Bou
> Responsable de Producto
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>
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