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From Dan Haywood <...@haywood-associates.co.uk>
Subject Re: Compuond objects
Date Fri, 06 Nov 2015 08:03:02 GMT
Hi David,
thanks for chipping in on this thread.  To answer your last question, I
think I agree very broadly with your analysis.  More detail within...


On 5 November 2015 at 20:08, David Tildesley <davotnz@yahoo.co.nz> wrote:

> Hi Cesar,
> I think you are saying you currently have :
>
> Business - ------> 1..* BusinessLocation
> Where one way navigation.
> Whereas in the first use case you want two way navigation so it looks like
> this:
> Business 1 <--------> 1..* BusinessLocation
>




> So if you have a BusinessLocation "in focus" then it is associated to
> single Business. This two way navigation between objects has always been an
> "expensive thing" to build - hence it is normally avoided unless the
> tradeoff suggests it should be done - but maybe ISIS makes this easier.
>

With JDO/DataNucleus, bidirectional relationships are no more difficult
than unidirectional.  With both bidirectional and undirectional, DN
supports either using a join table to hold the tuples between parent/child,
or alternatively a more traditional FK in the child.  I prefer to use a
join table for unidirectional, but FK for bidirectional; that way the
database tables model the domain classes quite nicely (in particular, with
a unidirectional and a join table the child table doesn't "know" about its
parent).



> But it sounds like you want a view which consolidates the information from
> one graph instance of the above into a single "form". So I believe the
> correct answer is yes: that is what the View Model is for. In terms of
> update behaviour - you need to add the operation on the View Model that
> explicitly sets the values on the domain object graph and persists them - I
> would suggest a single operation on Business for that purpose because
> Business should know about it's BusinessLocations - you pass the user
> values in including the BusinessLocation.id because Business has to know
> which BusinessLocation to update.
> Put all your View models in a separate package - they are not part of the
> domain. Make sure all the domain behaviour belongs to the domain objects
> and doesn't leak out into View objects. Never reference a View Model from
> the Domain Model the dependency should be View --> Domain and never the
> other way around. Domain is stable, View is volatile. Just create as many
> View Models as you need for the UI - after all that is what they are for.


What you are saying is true in this case, but you'll remember a long thread
from about a year ago when we enumerated various different "types" of view
model.  We came to the conclusion that the view model implementation is
also appropriate for what are really domain entities that just happen to be
persisted externally, eg over a SOAP service.

We express this using the @DomainObject(nature=...) attribute [1]



> In fact your application may not need to expose any domain objects as
> naked objects - but then again, there may some user experience downside to
> that (e.g. having to explicit operation for update).
> Folk - correct me if I am wrong - I need to catch up with where ISIS is
> currently at and so having folk correct me is very welcome for my education.
>

As per.  If you're just catching up, check out:

- changes to Isis itself in the release notes [2] ; 1.10.0 is imminent.
- (non ASF) Isis addons, [3]  - for reusable cross-cutting concerns
- (non ASF) incode catalog, [4]  - for reusable business functionality



> Regards,David.
>
>
>
Thx
Dan


[1]
http://isis.apache.org/guides/rg.html#_rg_annotations_manpage-DomainObject_nature
[2] http://isis.apache.org/release-notes.html
[3] http://www.isisaddons.org/
[4] http://catalog.incode.org/





>
>
>
>      On Friday, 6 November 2015 4:16 AM, Cesar Lugo <
> cesar.lugo@sisorg.com.mx> wrote:
>
>
>  Hello. I have the need to create some objects that are compound from some
> other domain objects (similar to a "view" in a relational database,
> updatable views). Let's say I have Business with businessId and name
> properties, 1:n to another entity named BusinessLocation with properties
> businessLocationId and name and address properties (to keep things simple
> for now). So, for example, I need to create a new object that is
> BuisinessLocationView, which contains BuinessLocation.id,
> BusinessLocation.name, Business.id and Buiness.name . Then, in some cases,
> I
> want to use such views like BusinessLocationView as a collection within
> Business, and as a standalone collection, and also have the ability to
> update its fields so the corresponding entities are updated with the
> changes
> (Business and BusinessLocation), and in some cases even add a new view like
> BusinessLocationView so it adds a new BusinessLocation.
>
>
>
> Is there a way to do this? Is that what @ViewModel is for?
>
>
>
> I would appreciate If you could point me to any sample that might help.
>
>
>
> Cesar.
>
>
>
>
>
>
>
> ---
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>
>
>
>

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