You are viewing a plain text version of this content. The canonical link for it is here.
Posted to users@wicket.apache.org by Johannes Schneider <ma...@cedarsoft.com> on 2009/03/04 13:50:18 UTC
How (not) to: IModel and Collections (and generics)
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
---------------------------------------------------------------------
To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
For additional commands, e-mail: users-help@wicket.apache.org
Re: How (not) to: IModel and Collections (and generics)
Posted by Johannes Schneider <ma...@cedarsoft.com>.
Thanks for your reply. I think I can (at least partially) understand
your position and think there aren't any new arguments here I can
mention. So the discussions seems to be at an end here.
Maybe it is a matter of taste... If I find any time, I will create a
patch...
Regards,
Johannes
On Sat, 2009-03-07 at 12:40 -0800, Igor Vaynberg wrote:
> you are right, the components that just read a collection do just
> that, read it. they simply ignore the setter method in imodel. no big
> deal, just because you are given an interface doesnt mean you have to
> use all the methods in it. thus abstractreadonlymodel.
>
> however, a lot of components manipulate items in the collection. you
> are right, they can do this without ever needing a setter, but it is
> very convenient to have a callback that lets you know that the
> collection has been updated. it is even more convenient to have a
> callback be part of model itself because in wicket you often factor
> out conversions and other transformations into the model
> implementation itself so they are reusable across multiple components.
> keep in mind models are the glue between components and your domain
> model, so if any kind of massaging needs to be done for the domain
> model to work smoothly with the component the model is the perfect
> place to do it.
>
> -igor
>
> On Sat, Mar 7, 2009 at 12:25 PM, Johannes Schneider
> <ma...@cedarsoft.com> wrote:
> >
> >> i think "misuse" is a pretty bold word considering you are talking to
> >> people who designed and built imodel, dont you think? :)
> >
> > Well, I think you are right. Sorry for that.
> > I just mean, that it has a bad smell here...
> >
> >>
> >> 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.
> >
> > Yes, I think we need at least two interfaces. I don't know whether we
> > need the icollectionmodel... I think that can be discussed.
> >>
> >> 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);
> >> }
> >
> > Don't know, whether that is really "elegant". It feels more like a
> > misuse... ;).
> > I think there is a reason you don't simply take an object for everything
> > (what might be the most elegant)...
> >
> > I really don't understand why IModel must handle the conversion stuff.
> > That conversion thing could/should be done using some wrapper or
> > something else. But I don't get all the concepts of Wicket.
> > I just think that components that just *read* a collection, should just
> > read the collection...
> >
> > But well, as you mentioned correctly, you have designed it, so it is
> > your choice...
> >
> >
> > Regards,
> >
> > Johannes
> >
> >
> >>
> >> -igor
> >>
> >> >
> >> > Regards,
> >> >
> >> > Johannes
> >> >
> >> > >
> >> > > -igor
> >> > >
> >> > > On Wed, Mar 4, 2009 at 4:50 AM, Johannes Schneider
> >> > > <ma...@cedarsoft.com> 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
> >> > > >
> >> > > >
> >> > > >
> >> > > >
> >> > > >
> >> > > >
> >> > > >
> >> > > >
> >> > > >
> >> > > >
> >> > > >
> >> > > >
> >> > > >
> >> > > > ---------------------------------------------------------------------
> >> > > > To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
> >> > > > For additional commands, e-mail: users-help@wicket.apache.org
> >> > > >
> >> > > >
> >> > >
> >> > > ---------------------------------------------------------------------
> >> > > To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
> >> > > For additional commands, e-mail: users-help@wicket.apache.org
> >> > >
> >> >
> >> >
> >> > ---------------------------------------------------------------------
> >> > To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
> >> > For additional commands, e-mail: users-help@wicket.apache.org
> >> >
> >>
> >> ---------------------------------------------------------------------
> >> To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
> >> For additional commands, e-mail: users-help@wicket.apache.org
> >>
> >
> >
> > ---------------------------------------------------------------------
> > To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
> > For additional commands, e-mail: users-help@wicket.apache.org
> >
> >
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
> For additional commands, e-mail: users-help@wicket.apache.org
>
---------------------------------------------------------------------
To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
For additional commands, e-mail: users-help@wicket.apache.org
Re: How (not) to: IModel and Collections (and generics)
Posted by Igor Vaynberg <ig...@gmail.com>.
you are right, the components that just read a collection do just
that, read it. they simply ignore the setter method in imodel. no big
deal, just because you are given an interface doesnt mean you have to
use all the methods in it. thus abstractreadonlymodel.
however, a lot of components manipulate items in the collection. you
are right, they can do this without ever needing a setter, but it is
very convenient to have a callback that lets you know that the
collection has been updated. it is even more convenient to have a
callback be part of model itself because in wicket you often factor
out conversions and other transformations into the model
implementation itself so they are reusable across multiple components.
keep in mind models are the glue between components and your domain
model, so if any kind of massaging needs to be done for the domain
model to work smoothly with the component the model is the perfect
place to do it.
-igor
On Sat, Mar 7, 2009 at 12:25 PM, Johannes Schneider
<ma...@cedarsoft.com> wrote:
>
>> i think "misuse" is a pretty bold word considering you are talking to
>> people who designed and built imodel, dont you think? :)
>
> Well, I think you are right. Sorry for that.
> I just mean, that it has a bad smell here...
>
>>
>> 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.
>
> Yes, I think we need at least two interfaces. I don't know whether we
> need the icollectionmodel... I think that can be discussed.
>>
>> 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);
>> }
>
> Don't know, whether that is really "elegant". It feels more like a
> misuse... ;).
> I think there is a reason you don't simply take an object for everything
> (what might be the most elegant)...
>
> I really don't understand why IModel must handle the conversion stuff.
> That conversion thing could/should be done using some wrapper or
> something else. But I don't get all the concepts of Wicket.
> I just think that components that just *read* a collection, should just
> read the collection...
>
> But well, as you mentioned correctly, you have designed it, so it is
> your choice...
>
>
> Regards,
>
> Johannes
>
>
>>
>> -igor
>>
>> >
>> > Regards,
>> >
>> > Johannes
>> >
>> > >
>> > > -igor
>> > >
>> > > On Wed, Mar 4, 2009 at 4:50 AM, Johannes Schneider
>> > > <ma...@cedarsoft.com> 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
>> > > >
>> > > >
>> > > >
>> > > >
>> > > >
>> > > >
>> > > >
>> > > >
>> > > >
>> > > >
>> > > >
>> > > >
>> > > >
>> > > > ---------------------------------------------------------------------
>> > > > To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
>> > > > For additional commands, e-mail: users-help@wicket.apache.org
>> > > >
>> > > >
>> > >
>> > > ---------------------------------------------------------------------
>> > > To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
>> > > For additional commands, e-mail: users-help@wicket.apache.org
>> > >
>> >
>> >
>> > ---------------------------------------------------------------------
>> > To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
>> > For additional commands, e-mail: users-help@wicket.apache.org
>> >
>>
>> ---------------------------------------------------------------------
>> To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
>> For additional commands, e-mail: users-help@wicket.apache.org
>>
>
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
> For additional commands, e-mail: users-help@wicket.apache.org
>
>
---------------------------------------------------------------------
To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
For additional commands, e-mail: users-help@wicket.apache.org
Re: How (not) to: IModel and Collections (and generics)
Posted by Johannes Schneider <ma...@cedarsoft.com>.
> i think "misuse" is a pretty bold word considering you are talking to
> people who designed and built imodel, dont you think? :)
Well, I think you are right. Sorry for that.
I just mean, that it has a bad smell here...
>
> 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.
Yes, I think we need at least two interfaces. I don't know whether we
need the icollectionmodel... I think that can be discussed.
>
> 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);
> }
Don't know, whether that is really "elegant". It feels more like a
misuse... ;).
I think there is a reason you don't simply take an object for everything
(what might be the most elegant)...
I really don't understand why IModel must handle the conversion stuff.
That conversion thing could/should be done using some wrapper or
something else. But I don't get all the concepts of Wicket.
I just think that components that just *read* a collection, should just
read the collection...
But well, as you mentioned correctly, you have designed it, so it is
your choice...
Regards,
Johannes
>
> -igor
>
> >
> > Regards,
> >
> > Johannes
> >
> > >
> > > -igor
> > >
> > > On Wed, Mar 4, 2009 at 4:50 AM, Johannes Schneider
> > > <ma...@cedarsoft.com> 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
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > ---------------------------------------------------------------------
> > > > To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
> > > > For additional commands, e-mail: users-help@wicket.apache.org
> > > >
> > > >
> > >
> > > ---------------------------------------------------------------------
> > > To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
> > > For additional commands, e-mail: users-help@wicket.apache.org
> > >
> >
> >
> > ---------------------------------------------------------------------
> > To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
> > For additional commands, e-mail: users-help@wicket.apache.org
> >
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
> For additional commands, e-mail: users-help@wicket.apache.org
>
---------------------------------------------------------------------
To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
For additional commands, e-mail: users-help@wicket.apache.org
Re: How (not) to: IModel and Collections (and generics)
Posted by Igor Vaynberg <ig...@gmail.com>.
On Sat, Mar 7, 2009 at 10:15 AM, Johannes Schneider
<ma...@cedarsoft.com> 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
> > <ma...@cedarsoft.com> 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
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > ---------------------------------------------------------------------
> > > To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
> > > For additional commands, e-mail: users-help@wicket.apache.org
> > >
> > >
> >
> > ---------------------------------------------------------------------
> > To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
> > For additional commands, e-mail: users-help@wicket.apache.org
> >
>
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
> For additional commands, e-mail: users-help@wicket.apache.org
>
---------------------------------------------------------------------
To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
For additional commands, e-mail: users-help@wicket.apache.org
Re: How (not) to: IModel and Collections (and generics)
Posted by Johannes Schneider <ma...@cedarsoft.com>.
On Wed, 2009-03-04 at 09:14 -0800, Igor Vaynberg wrote:
> components that deal with collections in wicket always reuse the same
> instance of collection is one was provided where it makes sense.
Yes, and therefore a setter is not necessary.
> 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?
Regards,
Johannes
>
> -igor
>
> On Wed, Mar 4, 2009 at 4:50 AM, Johannes Schneider
> <ma...@cedarsoft.com> 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
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > ---------------------------------------------------------------------
> > To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
> > For additional commands, e-mail: users-help@wicket.apache.org
> >
> >
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
> For additional commands, e-mail: users-help@wicket.apache.org
>
---------------------------------------------------------------------
To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
For additional commands, e-mail: users-help@wicket.apache.org
Re: How (not) to: IModel and Collections (and generics)
Posted by Igor Vaynberg <ig...@gmail.com>.
components that deal with collections in wicket always reuse the same
instance of collection is one was provided where it makes sense.
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.
-igor
On Wed, Mar 4, 2009 at 4:50 AM, Johannes Schneider
<ma...@cedarsoft.com> 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
>
>
>
>
>
>
>
>
>
>
>
>
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
> For additional commands, e-mail: users-help@wicket.apache.org
>
>
---------------------------------------------------------------------
To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
For additional commands, e-mail: users-help@wicket.apache.org
Re: How (not) to: IModel and Collections (and generics)
Posted by Johannes Schneider <ma...@cedarsoft.com>.
On Wed, 2009-03-04 at 08:27 -0800, Scott Swank wrote:
> Does AbstractReadOnlyModel accomplish what you're talking about?
Not really. I suggest a separate interface that does not extend IModel.
Instead IModel should extend that one (since it adds the setter)...
And of course that interface should be used within the declarations to
show that only read access is used...
Regards,
Johannes
>
> Scott
>
> On Wed, Mar 4, 2009 at 4:50 AM, Johannes Schneider
> <ma...@cedarsoft.com> 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
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > ---------------------------------------------------------------------
> > To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
> > For additional commands, e-mail: users-help@wicket.apache.org
> >
> >
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
> For additional commands, e-mail: users-help@wicket.apache.org
>
---------------------------------------------------------------------
To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
For additional commands, e-mail: users-help@wicket.apache.org
Re: How (not) to: IModel and Collections (and generics)
Posted by Scott Swank <sc...@gmail.com>.
Does AbstractReadOnlyModel accomplish what you're talking about?
Scott
On Wed, Mar 4, 2009 at 4:50 AM, Johannes Schneider
<ma...@cedarsoft.com> 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
>
>
>
>
>
>
>
>
>
>
>
>
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
> For additional commands, e-mail: users-help@wicket.apache.org
>
>
---------------------------------------------------------------------
To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
For additional commands, e-mail: users-help@wicket.apache.org