[jsr-314-open-mirror] [jsr-314-open] question regarding ajax update cycle

Werner Punz werner.punz at gmail.com
Wed Apr 7 08:26:38 EDT 2010 

It is not well designed but yet a valid component (as I said the issue
originated from an issue I got for myfaces and I gave also the root node
recommendation), as I said both approaches are broken, but an error
definitely has to be emitted in this case, I will do that on the client side
and warn the author of the component that it has to habe a root node with
the client id!
After all we have the error API in place, why not use it a little bit more
:-)
Also the spec clearly does just say that the code part with the client id
has to be replaced with the content of the CDATA block afair!

The main issue I have with the old approach compared to mojarras and our
newer approach
is, that if you just update the client id with the code junk coming in from
the client without taking the clientid itself into consideration you end up
with a broken dom tree, aka a dom tree with multiple nodes having the same
id, hence the behavior definitely is more broken in the old way than in the
new way.

The probably cleanest solution probably would be to stop the dom tree update
(and dont update) or leave the affected part blank, or with something which
signals that the area could not be updated due to the problem and raise the
error.

As for exposing the PartialResponseWriter API to the components in myfaces
only, this does not make sense too much it would bind the components to the
impl and I am not sure what the status about the approach is which hopefully
will go into 2.1. This needs to be fixed on the API side and should have
been before 2.0 went into production but that did not happen, probably
because it was too late when this issue was discovered.


Werner


On Wed, Apr 7, 2010 at 12:28 PM, Ganesh <ganesh at j4fry.org> wrote:

> Hi,
>
> I agree with Alexander. The component you posted is not well designed. As
> Alexander pointed out: What would getClientId() return for this component? I
> also agree with Alexanders solution: enclose the components reposne with a
> div that carries a proper clientId.
>
> It's an obvious characteristic of JSF AJAX to require having one HMTL
> element corresponding with one JSF component to be able to replace it via
> AJAX. Trying to craft a sophisticated solution for the cornercase of a badly
> designed component leads to a highly complicated specification enhancement
> that only makes sense to very few experts.
>
> Best regards,
> Ganesh
>
> Martin Marinschek schrieb:
>
>  Hi Werner,
>>
>> no. Don't follow any broken approach - emit an error saying that this
>> is not possible. Then the component author will know. Mojarra should
>> do the same.
>>
>> I agree that the API should be more open than. Can we expose this API
>> unilaterally at least in MyFaces?
>>
>> best regards,
>>
>> Martin
>>
>> On 4/7/10, Werner Punz <werner.punz at gmail.com> wrote:
>>
>>> The problem here is either behavior is wrong (not sure which is wronger),
>>> in
>>> the end the only real fix is to expose the full partialresponse writer
>>> API
>>> to the component author to give him full access on how his subpart on the
>>> page gets updated.
>>>
>>> This road currently is blocked simply by enforcing an open update tag on
>>> the
>>> components from the rendering lifecycle!
>>>
>>> The workaround is to make the component authors aware that for the PPR
>>> case
>>> within a component they always should make a root node which has the
>>> identifier of ClientId and embed their own rendering into this root node
>>> (div, span, whatever)
>>>
>>> So if I follow a broken approach I personally prefer to use the one which
>>> is
>>> consistent over all two implementations.
>>>
>>> In the end the only fix I know which makes sense to this problem is to
>>> add a
>>> marker interface to the spec
>>> something like PPRAware and a separate component renderer method,
>>> renderPPR
>>> and then adding placeholders for the component while the update tag is
>>> open,
>>> defer the rendering of the PPRAware component to the stage when update is
>>> closed
>>> and then render those deferred components by giving them control over the
>>> update, insert etc... possibilities wie theoretically have in the API and
>>> practically can only use outside of the render cycle :-(
>>>
>>>
>>>
>>>
>>> On Wed, Apr 7, 2010 at 9:26 AM, Martin Marinschek
>>> <mmarinschek at apache.org>wrote:
>>>
>>>  Hi guys,
>>>>
>>>> is it really useful to follow Mojarra's behaviour here? I think it
>>>> might be a little better to have a wandering div (and see that
>>>> something is wrong) than just ignoring the second div and with this
>>>> let the developer in the believe that everything is alright, which it
>>>> really isn't.
>>>>
>>>> best regards,
>>>>
>>>> Martin
>>>>
>>>> On 4/7/10, Werner Punz <werner.punz at gmail.com> wrote:
>>>>
>>>>> Yes that is what I was basically posting as workaround to the issue I
>>>>>
>>>> got,
>>>>
>>>>> nevertheless I now coded Mojarras behavior into MyFaces, just to be
>>>>> consistent here.
>>>>> (With the exception that I also fixed it on the IE side as Mojarra
>>>>>
>>>> behaves
>>>>
>>>>> for
>>>>> more compliant  browsers to have the same behavior over all browsers)
>>>>>
>>>>> I do not expect any component author really doing it differently than
>>>>> you
>>>>> said, Alex, but in the end to really resolve the problem we probably
>>>>> have
>>>>>
>>>> to
>>>>
>>>>> resolve the enforced update issue in the long run so that the
>>>>> PartialResponseWriter API can be used in its full extent and glory by
>>>>> the
>>>>> component authors instead of being shoehorned into an already open
>>>>> update
>>>>> tag!
>>>>>
>>>>> Werner
>>>>>
>>>>>
>>>>> On Wed, Apr 7, 2010 at 12:05 AM, Alexander Smirnov
>>>>> <asmirnov at exadel.com>wrote:
>>>>>
>>>>>  You have to keep in mind that JSF Ajax updates component content, not
>>>>>> the Html elements. Therefore, any component have to has enclosing Html
>>>>>> element ( <div> , <span> whatever else ) with id attribute generated
>>>>>> as
>>>>>> the component clientId to be compatible with Ajax. In your case, you
>>>>>> have to create placeholder element ( probably <div> ) that
>>>>>> encapsulates
>>>>>> both of your elements.
>>>>>>
>>>>>> On 04/06/2010 09:42 AM, Werner Punz wrote:
>>>>>>
>>>>>>> Hello everyone, I ran into an issue regarding the update, which is
>>>>>>> closely related to a behavior jsf2 exposes regarding component
>>>>>>>
>>>>>> rendering
>>>>
>>>>> in the update cycle.
>>>>>>>
>>>>>>> The main issue is following: If we have a component which we trigger
>>>>>>> with following code:
>>>>>>>
>>>>>>>  <myComp:javascriptTestComponent
>>>>>>> id="myTestComponent"></grv:javascriptTestComponent>
>>>>>>>                <a href="#" name="mego3"
>>>>>>>
>>>>>>> onclick="jsf.ajax.request(this,event,{execute:'myTestComponent',
>>>>>>> render:'myTestComponent'}); return false;">submit
>>>>>>>                    me</a>
>>>>>>>
>>>>>>> and the component itself renders following in its renderer:
>>>>>>>
>>>>>>>        ResponseWriter writer = context.getResponseWriter();
>>>>>>>        writer.startElement(DIV, component);
>>>>>>>        writer.writeAttribute(ID,component.getClientId(context), null
>>>>>>>
>>>>>> );
>>>>
>>>>>        writer.write("hello world"+Math.random());
>>>>>>>        writer.endElement(DIV);
>>>>>>>
>>>>>>>        writer = context.getResponseWriter();
>>>>>>>        writer.startElement(DIV, component);
>>>>>>>
>>>>>>> writer.writeAttribute(ID,component.getClientId(context)+":_second",
>>>>>>>
>>>>>> null
>>>>
>>>>> );
>>>>>>
>>>>>>>        writer.write("hello world"+Math.random());
>>>>>>>        writer.endElement(DIV);
>>>>>>>
>>>>>>>
>>>>>>> the resulting ppr response now looks like following:
>>>>>>>
>>>>>>> |<update id="myTestComponent">
>>>>>>>
>>>>>>> <![CDATA||[<div id="myTestComponent">hello
>>>>>>>
>>>>>> world0.8619488403376933</div>
>>>>
>>>>> <div id="myTestComponent:_second">hello||
>>>>>>>
>>>>>> world0.25176272071402683</div>]]>
>>>>>>
>>>>>>> </update>...|
>>>>>>>
>>>>>>> Now the problem is, since the update part of the response is already
>>>>>>> opened the component author cannot really influence the response
>>>>>>> rendering in any meaningful way (the correct solution would be to
>>>>>>>
>>>>>> issue
>>>>
>>>>> two update commands here)
>>>>>>> Now the javascript has to react on the client side to resolve that
>>>>>>> situation.
>>>>>>>
>>>>>>> Now MyFaces just replaced the original
>>>>>>>
>>>>>>> |myTestComponent|
>>>>>>>
>>>>>>> with the update code and hence the result was a div wandering down
>>>>>>>
>>>>>> (aka
>>>>
>>>>> wrong update)
>>>>>>>
>>>>>>> hello world0.48748236239247755
>>>>>>> hello world0.6020541783857698
>>>>>>> hello world0.7181842402648805
>>>>>>> hello world0.2803064696069696
>>>>>>> (after a handful of requests, with the lowest line being the first
>>>>>>> second div being dran)
>>>>>>>
>>>>>>> now due to being incorrect a user gave me rightfully a bug issue. I
>>>>>>>
>>>>>> dug
>>>>
>>>>> deeper and ran the same example
>>>>>>> against Mojarra, now Mojarra does cherry pick the delivered first div
>>>>>>> and replaces the original div, and omits the second one.
>>>>>>> The Problem is Mojarra just does it for newer browsers, it does the
>>>>>>>
>>>>>> same
>>>>
>>>>> just updating the  original element with the replacement code
>>>>>>> (and hence producing a wandering div) for IE6+7-
>>>>>>>
>>>>>>> My question is, first, how to handle that problem correctly.
>>>>>>> Secondly,
>>>>>>> is this even a problem for us or more one for the component author?
>>>>>>> In the end the main problem would not exist if they ajax api could be
>>>>>>> used on the component side properly without being enforced already
>>>>>>>
>>>>>> into
>>>>
>>>>> an update (or to allow nested updates, inserts within an update)
>>>>>>>
>>>>>>>
>>>>>>> Werner
>>>>>>>
>>>>>>>
>>>> --
>>>>
>>>> http://www.irian.at
>>>>
>>>> Your JSF powerhouse -
>>>> JSF Consulting, Development and
>>>> Courses in English and German
>>>>
>>>> Professional Support for Apache MyFaces
>>>>
>>>>
>>
>>
> --
> "There are two kinds of people in the world, those who believe there are
> two kinds of people and those who don't."
> — Robert Benchley
>
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