Good discussion.
Em 23/12/2009 15:32, Igor Vaynberg escreveu:
On Wed, Dec 23, 2009 at 7:02 AM, Ricardo Mayerhofer
<ricardo.ekm.lis...@gmail.com> wrote:
Hi Igor,
Thanks for your response. Here goes my observations:
Em 22/12/2009 14:41, Igor Vaynberg escreveu:
On Tue, Dec 22, 2009 at 5:19 AM, Ricardo Mayerhofer
<ricardo.ekm.lis...@gmail.com> wrote:
Hi all,
We've just finished with success a wicket project for a large online
retailer. I think wicket is the best framework out there, but as any
other
project there is room for improvement. I will talk about some topics
bellow,
I hope it can help in some way.
- Separation of corcerns
I think we could get a better separation of concerns if page class were
focused more in behavior and html were more focused in display (or view).
What I mean is, some times we have components that the main purpose is to
add behavior, and we have to add extra markup just to satisfy wicket 1:1
mapping. Take CheckGroup for exaple, it is a component focused on
behavior,
even though we have to add a reference to it in HTML.
a redesigned CheckGroup is welcome, but that component is the
exception and not the rule.
Yes, but how do we deal with the requirement of all components having a HTML
representation? The same happens with RadioGroup, even with wicket-1055
solved, the HTML reference is still there.
CheckGroup and RadioGroup are essentially the same thing as far as the
way they work. once you redesign CheckGroup the RadioGroup update will
be minimal.f
i dont think there is a big problem requiring every component to have
an html tag. after all wicket is a component based framework where
components represent ui which is in turn represented by html tags. the
tags also carry with them importance on nesting, so i also dont think
its a problem that wicket components carry the same importance.
I think that components should not represent UI, because if you do so
you will get a very strong coupling between both. I think it should be
there to add behavior to UI.
It's mainly a philosofical difference that has many implications. For
example, if we go with the last there won't be TextArea, TextField,
HiddenField and PasswordField. Only a text field component, that
represents behavior for this kind of input. The same for buttons and links.
You also solve checkgroup and radiogroup useless tag problem, and open
doors for components that the main purpose is to add behavior to the
page, even if not directly related to one specific tag.
That's the very example you gave, a webmarkupcontainer that controls
other components visibility. There is no need to map the container to HTML.
Also if we loose this coupling we can change java and html in a more
independent way, resulting in more flexibility.
come up with a list of usecases where this is inconvenient and if
there are a lot we can address them. but i cant really see many past
Check/RadioGroup components.
When creating composite input fields (like date), the usual way is to
create
a panel even if you are not interested in reusability. A interesting
aproach
is to insert a hidden text field in HTML mapped to a component that
controls
other components input. It makes easier to integrate with designer and to
preview in browser. If we didn't have this limitation the hidden input
would
not be necessary and the development of behavior focused components would
be
easier.
i dont really understand this..the usual way would be to extend a
FormComponentPanel, not a Panel. are you saying that because the Panel
derivatives are just a<div> in the markup it makes it difficult for
the designers?
You're right, I meant FormComponentPanel. I think it would be better not
being constrained to have a separate markup just because server side
processing will be different. After all in HTML terms, a composite input is
the same as a single input.
this has nothing to do with the difference in server-side processing,
this is more a design choice that promotes good reuse. lets say you
create a compound component that has two select boxes. if you do not
make it into a panel that means everywhere you use it you *have* to
know what kind of markup to put in, what the wicket:id values are for
the two select boxes that it uses, etc. in the future if you modify
this component to have a container around the two select boxes you now
have to find every place in your project where you used this component
and add the container. sounds like pita to me.
We usually start simpler and if required by another piece of
functionaly, we start generalizing and extracting components. Even if
you know from the start you need a reusable components, it's nice to
take baby steps, do the simpler, make it work, and then extract it.
It's great to have the option of getting a reusable composite component,
but the problem is that there is no way of doing different.
Another example of unecessary coupling IMO is
that text area and input text fields are mapped to different components,
even behaving the same.
Even if there are internals when manipulating one or another, I think it
should be handled by wicket because for the programmer it makes no
difference.
agreed. we already do this with links and buttons. my guess is that it
has never bothered anyone enough to create an rfe.
One thing that bothers me is when our designer move things around in HTML
and we get "added a component in code but forgot to reference it in the
markup" error, because of component hierarchy. Html tags position is a
view
problem not a behavior problem, so why bother in java?
it *is* a behavior problem. markup is what drives the rendering order
so if you move things around and change the nesting order of
components then you can have a component that is a child of another
render *before* the parent which will cause things to go seriously out
of whack.
in my company the designers understand that they cannot change the
nesting of tags with wicket:id attributes, it took an hour to explain
it to them, and we have not had any problems since. in practice, there
is no need to do that often anyways...
IMO learning how to deal with a restriction, isn't better than removing that
restriction. Even if it doens't happen often, I would be happier if it never
happens :)
Render order seems a wicket internal concern to me not a business or
application behavior concern.
render order has to be defined somewhere. it can either be defined in
the markup or it can be defined in your code. if it is defined in your
code by the sequence of add() calls then every time the designer wants
to move anything around (even sibling components) you will have to
change the code. with the render order coming from markup this
restriction is only when the nesting of components changes. which one
seems more restrictive to you?
None of them seem good to me. I don't know the solution but I would be
glad to help to come out with one.
it is nice to have a cop-out of "this is not a business concern", but
that doesnt really mean anything when discussing this does it? when
working on any application you are always restricted by the technology
you are using whether it be your web framework, your application
server, your database, your operation system, your server, your
backbone, etc..
Another issue, is when we want to change the class of a div, for example,
and have to change our whole page hierarchy in java, just to manipulate
that
tag.
you dont have to change the hierarchy, just make the component
attached to that div a "transparent resolver" by overriding
isTransparentResolver() and returning true.
So I think a hierarchy more focused on components behavior (for example
taking care of inherited models and inputs), rather than tags position in
HTML would be better. This would make wicket more flexible and easier to
work with.
once again, this is only a problem when you change the *nesting* of
components. if a component can be safely moved outside the parent,
then why is there a nesting to begin with? why arent the two
components siblings? the *nesting* is usually there *because* there is
a functional requirement.
here is a simple usecase:
webmarkupcontainer admin=new webmarkupcontainer("admin") { isvisible()
{ return user.isadmin(); }};
admin.add(new link("delete") {...});
the code is pretty much self-explanatory, now the designer takes the
delete link and moves it ouside the wicket:id="admin" tag. in your
vision this would work, but now the designer has completely
circumvented security the developer has put into place.
They have a functional relationship, so no matter where delete link is in
HTML, it should be invisible. This has a aditional advantage that I do not
need to map admin to HTML, and can group another admin functions in the same
component, even if they're scattered.
and how would you define this "functional" relationship. it is very
convenient to be able to control certain things such as visiblity and
enabled state on a parent in order to be able to easily propagate it
to children.
we are always ears for new good ideas, but it takes more then "it
should work like this".
You're right, I'm talking about ideas here, but as above I would be glad
to help if there is some acceptance of those or openness to discuss it
further.
- Too many finals modifiers
It's hard for a API or framework designer to foresee all uses and
unxepected
situations its users may face in day to day development. Final modifiers
places a additional challenge when facing these situations. In project
were
deadlines are in place, there is little room for submiting a request and
waiting for a new version to be released. Furthermore, unfortunately,
it's
not possible to mock final methods making it harder sometimes to test
wicket
related classes/components. What we had to do internally, is to have our
own
version of wicket, mainly to remove final modifiers when necessary, a
clear
violation of open/closed principle.
there is a trade off here. the final modifiers allow us to change
things below without breaking the api because final methods do not
expose a contract. when we make a code change inside a final method we
do not have to think about all the users out there who might have
potentially overridden the method in their apps and we have to make
whatever change backwards-compatible.
in short, the upgrade path with final methods looks like this:
1.4.0,1.4.1,...,1.4.8,1.4.9
and the path without final methods would look like this:
1.4.0,1.4.1,1.5.0 (api break),1.5.1, 1.6.0 (api break), 1.7.0 (api break)
and because we are changing contracts the api break would most likely
not be compile time, so you would have to scour through release notes
and see if you have overridden any of the specified methods that now
work differently.
which one is better?
Being able to overcome a problem is a need required by the current project,
which final may impose a additional challenge.
Upgrades, on the other hand, are usually planned process, in which are
considered possible problems or API changes.
so now to get almost any bug fix you have to recompile, change code,
and redeploy the entire application. that seems like a highly risky
proposition. it basically means you can never really retire an
application that is feature-complete and simply drop new wars in to
get bug fixes, you always have to have active development on it. i
dont think many people will buy this approach.
I think spring is a good example in this area. It has a pretty good backward
compatibily, and use very few finals.
you are comparing apples to oranges. you do not write your application
"in" spring. spring is all about staying out of your code, so of
course they can do whatever the hell they want because they have very
few public apis. wicket, on the other hand, is opposite. in wicket
most apis *are* public and you use them in your code. we do not
provide interfaces for the same reason we use final methods, we do not
want to lock ourselves into a contract.
Spring also has Spring MVC and spring web flow as part of it. If I
remember correctly Rod Johnson, is a advocator of avoiding static,
singletons and finals.
Wicket is the only framework I remember that uses final as a aproach for
backward compatibility. That makes me wonder if there is a real problem
of not doing so and if there is alternatives.
another point is that neither one of us has any visibility into the
internal development of spring. you are making this observation seeing
only the final product, but do you know how many times a core spring
developer thought to himself: damn, if only this method was final i
could throw in this new cool feature into the next minor release, or
better yet, damn if only this method was final i could fix this bug in
the next minor release instead of the next major one.
About contracts, I think that they should be specified in terms of
interfaces, not concrete classes. If you depend on concrete classes, it's
natural that they evolve and may break your integration.
so its ok if the next minor jdk update changes the api of String?
thats a concrete class...
I don't remember JDK using many finals :)
Wicket offers no stateless ajax
we may work on a stateless ajax in the future, for now it is really
not that hard to use a third party library.
and often changes HTML id, which makes
harder to integrate with a 3rd party ajax framework.
wicket only changes ids that belong to components, and that is only to
make sure they are unique. wicket does , however, offer a way to
override the id to whatever you want by calling setMarkupId(..)
the proper way to integrate with third party libraries is to pass them
ids by calling getmarkupid()
Many of things I raised (or all of them) have solutions in wicket. But I
think it's best when the framework solves the problem, rather than doing it
myself. That's why we use frameworks in the first place.
yes, it would be great to have an easy button. unfortunately every
application out there is different and there is no way we can provide
a set of defaults that will work for everyone out there.
we strive to hit the point at which "easy things are easy and hard
things are possible".
I can't see how a application would benefit of having its HTML ID
changed if there isn't the same identifier another place in the
document. Sometimes I don't think it's about solving everyone problem,
but about keeping possible problems away.
Is there any hope for
constructor change?
what constructor change is that?
From the discontinued 2.0.
there was a reason why 2.0 was discontinued. the constructor change
made some things that were easy before hard, and some things that were
possible before not possible anymore. the constructor change also did
not solve any of the issues that we have discussed here so i dont even
see how it is relevant.
I thought it would help integration with ajax and javascript that
requires html id, but I could get it wrong.
-igor
-igor
Thank you for your feedback.
Please let me know your thoughts, keep up the good work.
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