On Sat, Mar 7, 2009 at 10:15 AM, Johannes Schneider
<[email protected]> wrote:
>
> > setobject is still called on the model, but is called with the same
> > instance of collection. this is necessary so that if you have a model
> > that translates a collection of one type to a collection of another
> > can perform the conversion when the component pushes new data into it.
>
> And this is just a *misuse* of the given method... Why not create a own
> model interface for collections and add some sort of conversion
> method/object?
i think "misuse" is a pretty bold word considering you are talking to
people who designed and built imodel, dont you think? :)
if we do what you suggest then we would end up with:
interface imodel { object getobject(); }
interface icollectionmodel extends imodel { object convert(object); }
interface iwhatevermodel extends imodel { void setobject(object); }
then things that are built on top of imodel now have to be built on
top of at least two hierarchies (imodel and iwhatevermodel -
considering icollectionmodel can be a mixin which all implementations
have to check for which makes it dirty), so we will end up with double
the classes like loadabledetachablemodel, etc.
where as right now this works perfectly and is quiet elegant:
abstract class collectionconverter<new,old> implements imodel<collection<new>> {
private final imodel<collection<old>> delegate;
public collection<new> getobject() {
list<new> list=new arraylist<new>(delegate.getobject().size());
for (old o:delegate.getobject()) {
list.add(converttonew(o));
}
return list;
}
public void setobject(collection<new> object) {
delegate.getobject().clear();
for (new o:object) {
delegate.getobject().add(converttold(o));
}
}
abstract new converttonew(old o);
abstract old converttoold(new o);
}
-igor
>
> Regards,
>
> Johannes
>
> >
> > -igor
> >
> > On Wed, Mar 4, 2009 at 4:50 AM, Johannes Schneider
> > <[email protected]> wrote:
> > > Hi,
> > >
> > > the concept of IModel seems to be very obvious. It is simply some kind
> > > of reference and offers a getter and a setter.
> > >
> > > When used with ordinary object, everything works fine. An IModel that
> > > contains a String can easily be mapped to a TextField.
> > > The text field calls "getObject" to show the initial value and sets the
> > > changed string to the model using "setObject" on form commit.
> > >
> > >
> > > Everything becomes a little more complicated when collections are
> > > affected. The problem is, that it is not obvious what those collections
> > > represent.
> > >
> > > 1) A collection might be read-only (e.g. the possible choices for a
> > > selection).
> > > 2) But it also might be necessary to add/remove single elements (e.g.
> > > privileged users shown within a shuffle list).
> > > 3) And sometimes the complete collection is changed (can't find an
> > > example here).
> > >
> > >
> > > IModel only supports the *third* method where the complete collection is
> > > replaced.
> > > (Don't forget that the reference to the collection changes which will
> > > lead to several other problems.)
> > > I strongly recommend the usage of a wrapping class for that case.
> > > But this case is not very common. Maybe someone finds a good example - I
> > > can't.
> > >
> > >
> > > For the other two cases it does *not* make any sense to call
> > > IModel#setObject.
> > >
> > >
> > > Summary: Nearly in every case when the IModel contains a collection, the
> > > "setObject" method does not make any sense and must not be called.
> > >
> > >
> > > Conclusion: I think we should have created some sort of IModelProvider
> > > (contains only the getObject method) and IModel (with both methods).
> > > Components that just *read* values from the model, accept the read only
> > > interface now.
> > >
> > > For special cases where a magic component adds/removes elements to a
> > > collection, we need some sort of ICollectionModel that offers "add" and
> > > "remove" methods (but no setter).
> > > That interface - of course - will be based upon a collection *without*
> > > wildcards...
> > >
> > >
> > >
> > > Regards,
> > >
> > > Johannes Schneider
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
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> > >
> >
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