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
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