Ok, let me just recap the motivation for qualifiers and what it is
supposed to achieve.
The goal (in the discussion that I participated in but later was absent
from) was to achieve something like association classes in UML.
Example A has a collection of Bs and you need to track the date when the
association was introduced.
A and B are entities. Is the association from an A to a particular B an
entity, no I don't think so.
Does it become an entity just because you need to know when the
association was introduced, no I don't think so either.
This is why there was an attempt to further qualify the relation without
introducing another entity.
Why is the qualified relation not an entity?
It has no identity, there is simply no need to track one and the same
association, it suffices to know what data is attached to the unique
association between a particular instance of A to a particular instance
of B.
The qualifier construct is supposed to make it explicit that it is just
some data being unique to an association between entities.
I think that a good api for this would enhance the understandability of
the model.
/Niklas
Michael Hunger wrote:
Encapsulating the qualification in concrete Entities of the ManyAssoc
makes more sense for me. It also is a better
design to have concrete types representing this qualified association.
The other way would be like cascading maps (which I don't like at all).
http://www.jexp.de/demotivators/cascading_collections.jpg
Michael
Am 03.04.2009 8:07 Uhr, schrieb Rickard Öberg:
Niclas Hedhman wrote:
On Fri, Apr 3, 2009 at 1:10 PM, Rickard Öberg <[email protected]>
wrote:
interface Movie
extends EntityComposite
{
@Aggregated
ManyAssociation<Casting> cast();
}
and then separately
interface Casting
extends EntityComposite
{
Association<Actor> actor();
Association<Role> role();
}
What say ye?
I never got my head twisted around Qualifiers, so can't really balance
in the advantages of it.
If nothing else; It is easier to;
1. Explain
2. Understand
3. Implement in Qi4j Runtime
so, I think it is a win.
Ok, so both Qualifiers and events are out. That's going to drastically
simplify things :-)
/Rickard
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