Re: ISIS-970 ... (new annotations) please review if you get a chance...

[David Tildesley <da...@yahoo.co.nz>]

Hi Jeremy,
That's correct.
Regards,David. 

     On Thursday, 1 January 2015 11:48 AM, "Branham, Jeremy [HR]" <Je...@sprint.com> wrote:
   

 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:davotnz@yahoo.co.nz]
Sent: Wednesday, December 31, 2014 4:36 PM
To: dev@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 <da...@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]" <Je...@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:jeroen@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>> 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 <vn...@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 <da...@haywood-associates.co.uk>>:


On 30 December 2014 at 23:44, David Tildesley <da...@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 < dan@haywood-associates.co.uk<ma...@haywood-associates.co.uk>> wrote:


On 29 December 2014 at 13:23, GESCONSULTOR - Óscar Bou < o.bou@gesconsultor.com<ma...@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
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