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From "Kevin Meyer" <ke...@kmz.co.za>
Subject Re: How to display value object
Date Tue, 15 Aug 2017 09:55:59 GMT
Hi Ekko,

I believe Dan has answered the question that you asked. However I think it
is worth mentioning that (as I see it), Apache Isis does not treat the
different objects in the way that I think you are considering them.

While DDD may make the distinction between "value" and "entity" e.g. [1],
in Apache Isis, all annotated objects are entities and persisted to the
database.

By annotating a "value" object e.g. in [2] with @PrimaryKey (and @Column),
you are declaring that that are to be persisted - that they are entities.

In your case "CustomerContactInfomation" is an entity. You just want to
subordinate maintenance and viewing to the Customer entity.

True DDD "value" objects (which are also immutable) would not be persisted
in their own table - there is no need and you'd fill up a table with old
entries that are no longer needed (the Location in the example [1]).
To me, the "immutable" aspect of a value object means that *if* you did
persist it to a table, you'd want to delete the old entry as soon as the
value changes or the reference count drops to zero.

In Apache Isis you would make them properties of the parent. It was once
possible to write ValueAdapters that could serialise a value class into 
(one or more) columns of the table used to persist the "parent" entity and
the framework would maintain (serialise/deserialise) these "value" object
properties for you.
However these ValueAdapters are no longer supported (the behaviour is now
achieved in other ways).

In short - in Apache Isis all "database" annotated objects are entities.
But you can tweak the presentation of data from these entities with the
use of annotations and actions (on the "parent") to enforce the
subordination expected of a "value" object.

Cheers,
Kevin

[1] http://culttt.com/2014/04/30/difference-entities-value-objects/
[2] https://stackoverflow.com/a/45662839/56880

> Hi support,
>
>
> I'm building project with Apache Isis,but I have some confusion.
>
>
> In DDD,I know there have two objects,entity & value object.
>
>
> When I plan a DomainObject,eg. Customer, a entity object. I think one
> Customer may be have many value objects,for example contact information
> or other value objects.
>
> So I plan a value object called CustomerContactInformation,may be have
> other value objects.
>
> For the database,a entity object and its value objects may be persist to
> diff tables.
>
> I think CustomerContactInformation just a value object,it can not have
> any actions and should be maintained by Customer.
>
> In fact,Customer-CustomerContactInfomation definitely is 1-1.
>
>
> Now,how should I display CustomerContactInformation in Customer's layout
> and be able to edit CustomerContactInformation?
>
> Any ideas?
>
>
> Ekko
>
>
>


-- 
Kevin Meyer
Ljubljana, Slovenia



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