Re: Unfriendly Model.ofList etc. methods; can anything be done?
On Sat, Feb 12, 2011 at 8:49 AM, Willis Blackburn wbo...@panix.com wrote: jer...@wickettraining.com wrote: On Sat, Feb 12, 2011 at 7:56 AM, Willis Blackburn wbo...@panix.com wrote: As a side note, rarely should you ever use Model class for a list of things, especially things loaded from a database. If you then pass that model to a component, all the things in it will be serialized. I'm sorry that I said that I loaded the list from a database, since that has apparently created a distraction from my key point, which is that if you start with a ListC and pass it to Model.listOf, you get back something that is not a ListC, which is undesirable and perhaps unnecessary. I understood your key point, which is why I said as a side note but my point still remains. Loading a list and then sticking it into Model class is in almost all cases a *bad* idea. So use the Model constructors instead. The factory methods are just there to help remove some verbosity related to generics. Have you tried this yourself? Because it doesn't work. You can only instantiate Model with a Serializable instance, and java.util.List does not implement Serializable. The whole point of the ofList method is to generate serializable lists, and the documentation even says so: This factory method will automatically rebuild a nonserializable list into a serializable one. You're confusing Model.listOf with Model.of. Sorry, yes, it was early and I wasn't paying attention. Hadn't had my Wheaties yet :) Have you looked at the ListModel class? It may help with what you're looking for. Do you have a suggestion for a better method signature for that method? The problem you are describing, if I understand your description correctly, is a problem with Java generics, not with Wicket's use of them. -- Jeremy Thomerson http://wickettraining.com *Need a CMS for Wicket? Use Brix! http://brixcms.org*
Re: Unfriendly Model.ofList etc. methods; can anything be done?
A simpler API would be: public static C IModelListC ofList(final List? extends C list) or even: public static C IModelListC ofList(final ListC list) since you are calling this method with a specific List, and hence the type of the List is known. Scott On Sun, Feb 13, 2011 at 11:32 AM, Jeremy Thomerson jer...@wickettraining.com wrote: On Sat, Feb 12, 2011 at 8:49 AM, Willis Blackburn wbo...@panix.com wrote: jer...@wickettraining.com wrote: On Sat, Feb 12, 2011 at 7:56 AM, Willis Blackburn wbo...@panix.com wrote: As a side note, rarely should you ever use Model class for a list of things, especially things loaded from a database. If you then pass that model to a component, all the things in it will be serialized. I'm sorry that I said that I loaded the list from a database, since that has apparently created a distraction from my key point, which is that if you start with a ListC and pass it to Model.listOf, you get back something that is not a ListC, which is undesirable and perhaps unnecessary. I understood your key point, which is why I said as a side note but my point still remains. Loading a list and then sticking it into Model class is in almost all cases a *bad* idea. So use the Model constructors instead. The factory methods are just there to help remove some verbosity related to generics. Have you tried this yourself? Because it doesn't work. You can only instantiate Model with a Serializable instance, and java.util.List does not implement Serializable. The whole point of the ofList method is to generate serializable lists, and the documentation even says so: This factory method will automatically rebuild a nonserializable list into a serializable one. You're confusing Model.listOf with Model.of. Sorry, yes, it was early and I wasn't paying attention. Hadn't had my Wheaties yet :) Have you looked at the ListModel class? It may help with what you're looking for. Do you have a suggestion for a better method signature for that method? The problem you are describing, if I understand your description correctly, is a problem with Java generics, not with Wicket's use of them. -- Jeremy Thomerson http://wickettraining.com *Need a CMS for Wicket? Use Brix! http://brixcms.org* - To unsubscribe, e-mail: users-unsubscr...@wicket.apache.org For additional commands, e-mail: users-h...@wicket.apache.org
Re: Unfriendly Model.ofList etc. methods; can anything be done?
On Feb 13, 2011, at 2:33 PM, jer...@wickettraining.com [via Apache Wicket] wrote: I understood your key point, which is why I said as a side note but my point still remains. Loading a list and then sticking it into Model class is in almost all cases a *bad* idea. I agree with you! But nevertheless there are some cases in which a ModelListC makes sense--even when a database is involved. If, for example, the List is small, and is expensive to generate from the database, then serializing it and keeping it in the session could be the best approach. Sorry, yes, it was early and I wasn't paying attention. Hadn't had my Wheaties yet :) Have you looked at the ListModel class? It may help with what you're looking for. Do you have a suggestion for a better method signature for that method? The problem you are describing, if I understand your description correctly, is a problem with Java generics, not with Wicket's use of them. I hadn't seen ListModel, but thanks--it looks like a good solution. Although it sort of makes Model.listOf even more mysterious, in that Model.listOf doesn't create a ListModel. My suggestion for Model.listOf is simply: public static C IModelListC ofList(final ListC list) In other words it takes a ListC and return an IModelListC, which is (I think) what you'd expect. Maybe the thinking is that Model.listOf may need to return a list of some serializable subclass of C, if C is not serializable itself. W -- View this message in context: http://apache-wicket.1842946.n4.nabble.com/Unfriendly-Model-ofList-etc-methods-can-anything-be-done-tp3302712p3304062.html Sent from the Users forum mailing list archive at Nabble.com. - To unsubscribe, e-mail: users-unsubscr...@wicket.apache.org For additional commands, e-mail: users-h...@wicket.apache.org
Unfriendly Model.ofList etc. methods; can anything be done?
I'm constantly running into problems with this method: public static C IModelList? extends C ofList(final List? extends C list) This says that ofList takes, as a parameter, a List of C or some subclass of C, and returns a List of C or of some subclass of C. The problem that I keep having is that the type of the input list and the type of the output list may not be the same. I think that in practice they are, but the compiler does not know that. If C = StringedInstrument then the parameter may be ListViolin while the returned list may be ListGuitar. So every time I call Model.listOf, the type parameter of my List becomes hazy, which has annoying downstream effects. If I load a ListStringedInstrument from a database, then pass it to Model.ofList, I wind up with a List? extends StringedInstrument--the compiler has no idea what the generic type of the List is, only that whatever it is, it is compatible with StringedInstrument. I can still get StringedInstrument instances out of the List, but I can't pass it to any method (like a component constructor) that takes a ListStringedInstrument or an IModelListStringedInstrument without ugly casting. Since Model.ofList must return a list that is compatible with the original list--it's a wrapper, not a transformer--can't it just take ListC and return ListC? Same goes for the other ofCollection-type methods. -- View this message in context: http://apache-wicket.1842946.n4.nabble.com/Unfriendly-Model-ofList-etc-methods-can-anything-be-done-tp3302712p3302712.html Sent from the Users forum mailing list archive at Nabble.com. - To unsubscribe, e-mail: users-unsubscr...@wicket.apache.org For additional commands, e-mail: users-h...@wicket.apache.org
Re: Unfriendly Model.ofList etc. methods; can anything be done?
On Sat, Feb 12, 2011 at 7:56 AM, Willis Blackburn wbo...@panix.com wrote: I'm constantly running into problems with this method: public static C IModelList? extends C ofList(final List? extends C list) This says that ofList takes, as a parameter, a List of C or some subclass of C, and returns a List of C or of some subclass of C. The problem that I keep having is that the type of the input list and the type of the output list may not be the same. I think that in practice they are, but the compiler does not know that. If C = StringedInstrument then the parameter may be ListViolin while the returned list may be ListGuitar. So every time I call Model.listOf, the type parameter of my List becomes hazy, which has annoying downstream effects. If I load a ListStringedInstrument from a database, then pass it to Model.ofList, I wind up with a List? extends StringedInstrument--the compiler has no idea what the generic type of the List is, only that whatever it is, it is compatible with StringedInstrument. As a side note, rarely should you ever use Model class for a list of things, especially things loaded from a database. If you then pass that model to a component, all the things in it will be serialized. You should be using LoadableDetachableModel and have the load from database logic in the load method. Model is just a dataholder implementation of IModel that should typically only be used for transient data (data that can't be loaded from somewhere) because it must serialize whatever you get it. This is especially bad whenever you are dealing with any collection of things. I can still get StringedInstrument instances out of the List, but I can't pass it to any method (like a component constructor) that takes a ListStringedInstrument or an IModelListStringedInstrument without ugly casting. Since Model.ofList must return a list that is compatible with the original list--it's a wrapper, not a transformer--can't it just take ListC and return ListC? Same goes for the other ofCollection-type methods. So use the Model constructors instead. The factory methods are just there to help remove some verbosity related to generics. -- Jeremy Thomerson http://wickettraining.com *Need a CMS for Wicket? Use Brix! http://brixcms.org*
Re: Unfriendly Model.ofList etc. methods; can anything be done?
jer...@wickettraining.com wrote: On Sat, Feb 12, 2011 at 7:56 AM, Willis Blackburn wbo...@panix.com wrote: As a side note, rarely should you ever use Model class for a list of things, especially things loaded from a database. If you then pass that model to a component, all the things in it will be serialized. I'm sorry that I said that I loaded the list from a database, since that has apparently created a distraction from my key point, which is that if you start with a ListC and pass it to Model.listOf, you get back something that is not a ListC, which is undesirable and perhaps unnecessary. So use the Model constructors instead. The factory methods are just there to help remove some verbosity related to generics. Have you tried this yourself? Because it doesn't work. You can only instantiate Model with a Serializable instance, and java.util.List does not implement Serializable. The whole point of the ofList method is to generate serializable lists, and the documentation even says so: This factory method will automatically rebuild a nonserializable list into a serializable one. You're confusing Model.listOf with Model.of. W -- Jeremy Thomerson http://wickettraining.com *Need a CMS for Wicket? Use Brix! http://brixcms.org* -- View this message in context: http://apache-wicket.1842946.n4.nabble.com/Unfriendly-Model-ofList-etc-methods-can-anything-be-done-tp3302712p3302752.html Sent from the Users forum mailing list archive at Nabble.com. - To unsubscribe, e-mail: users-unsubscr...@wicket.apache.org For additional commands, e-mail: users-h...@wicket.apache.org
