[seam-dev] In list.xhtml.ftl, what is the point of the foreach for the create button if Pages.applyConvertedValidatedValuesToMode cannot deal with nulls in parameters?
Dan Allen
dan.j.allen at gmail.com
Sat Mar 14 03:59:28 EDT 2009
And you you're other question, yes, the following is a simple way of
disabling the page parameter for a link:
<f:param name="paramName"/>
Hence the loop. Yes, usePageParams="false" would also work.
-Dan
On Sat, Mar 14, 2009 at 3:58 AM, Dan Allen <dan.j.allen at gmail.com> wrote:
> I actually came across this issue while working on the design of view
> parameters for JSF 2.0. It's a tricky problem because sometimes you just
> want the parameter to be discarded if it is null and sometimes you want that
> null value to clear the property on the model.
>
> If we think about the goal of page parameters, they are there to map an
> inbound request parameter to the property of a model. The mapping is there
> to kick things off. The absence of a request parameter cannot be assumed to
> mean that you want to nullify the model. Otherwise, the page parameters
> would always be required and thus overstepping their bounds (which is
> exactly the situation you have with using them w/ a long-running
> conversation). If you want to clear the model out of the conversation, you
> should be using a command, whether it be a command button or a page action.
> Only then can you be sure that setting the value to null is the desired
> operation. You can easily pass a parameter hint like create=true to tell the
> page action to clear out any previous model value and start with a fresh
> form.
>
> Keep in mind that the application seam-gen creates is a starting point, not
> a design best practice. If the button it creates is not handling the
> situation properly, then add some extra code to make it work.
>
> -Dan
>
> On Mon, Dec 8, 2008 at 12:52 PM, Francisco Jose Peredo <
> franciscoperedo at tabasco.gob.mx> wrote:
>
>> Hi!
>> The code for the create button in list.xhtml.ftl looks like this:
>>
>> <s:div styleClass="actionButtons" rendered="${'#'}{empty from}">
>> <s:button view="/${editPageName}.xhtml"
>> id="create"
>> propagation="none"
>> value="Create ${componentName}">
>> <#assign idName = componentName + pojo.identifierProperty.name?cap_first>
>> <#if c2j.isComponent(pojo.identifierProperty)>
>> <#foreach componentProperty in
>> pojo.identifierProperty.value.propertyIterator>
>> <#assign cidName = componentName + componentProperty.name?cap_first>
>> <f:param name="${cidName}"/>
>> </#foreach>
>> <#else>
>> <f:param name="${idName}"/>
>> </#if>
>> </s:button>
>> </s:div>
>>
>> That generates a <f:param name="${idName}"/> for the primarykey(s). Why is
>> that done? My best guess is that it is to clear the value
>> of the primary key for the new object that is going to be created.
>>
>> But the <f:param name="${idName}"/> actually does nothing, because in seam
>> it is impossible to set a parameter to null. This f:params are AFAIK
>> expected to set the method generated in EntityHome.java.ftl:
>>
>> public void set${idName}(${idType} id)
>> {
>> setId(id);
>> }
>>
>> But that set is never going to be called for <f:param name="${idName}"/>
>> because the id value is null! And there is code to prevent
>> set${idName}(${idType} id) from being called if the value for the id is
>> going to be null in Pages.applyConvertedValidatedValuesToMode:
>>
>> private void applyConvertedValidatedValuesToModel(FacesContext
>> facesContext)
>> {
>> String viewId = getViewId(facesContext);
>> for ( Page page: getPageStack(viewId) )
>> {
>> for ( Param pageParameter: page.getParameters() )
>> {
>> ValueExpression valueExpression =
>> pageParameter.getValueExpression();
>> if (valueExpression!=null)
>> {
>> * Object object = Contexts.getEventContext().get(
>> pageParameter.getName() );
>> if (object!=null) //<--- HERE IS THE PROBLEM
>> {
>> valueExpression.setValue(object);
>> }*
>> }
>> }
>> }
>> }
>>
>> Of course, it gives the impression it works, but that is just because our
>> EntityHome is recently created and the value for the Id is initially null.
>> But if we place our EntityHome inside a LRC, and try to use after a previous
>> creation set the value of the Id, we will see that the Id is not reset to
>> null by the <f:param name="${idName}"/>
>>
>> A workaround I use when the id is Integer is this the -1 value:
>>
>> <f:param name="${idName}" value="-1"/>
>>
>> public void set${idName}(${idType} id)
>> {
>> if(id<0){
>> setId(null);
>> }else{
>> setId(id);
>> }
>> }
>>
>> But that, as it was commented in another null related discussion, a really
>> ugly way to deal with stuff we want to be "undefined". So what can be done
>> to fix this in Seam/seam-gen? (And of course offer a solution that can be
>> used as a "best practice" for dealing with this even in applications that do
>> not use seam-gen).
>>
>> I propose removing the if (object!=null) from
>> applyConvertedValidatedValuesToModel (and maybe other methods in Pages that
>> avoid dealing with nulls in the same limited way? like perhaps
>> convertAndValidateStringValuesInPageContext? and getStringValuesFromModel?
>> and storeRequestStringValuesInPageContext? and possibly others...).
>>
>> Now, if ignoring null values for page parameters in this way is not a bug,
>> but a feature, then I propose removing the foreach for the create button
>> list.xhtml.ftl, because it just creates the false impression that <f:param
>> name="${idName}"/> actually does something.
>>
>> I already created a related JIRA a while ago (
>> https://jira.jboss.org/jira/browse/JBSEAM-3693) but guess I was not able
>> to correctly explain this problem, I hope to have better luck this time.
>>
>> Regards,
>> Francisco Peredo
>>
>>
>> --
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>
>
> --
> Dan Allen
> Senior Software Engineer, Red Hat | Author of Seam in Action
>
>
> http://mojavelinux.com
> http://mojavelinux.com/seaminaction
>
> NOTE: While I make a strong effort to keep up with my email on a daily
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--
Dan Allen
Senior Software Engineer, Red Hat | Author of Seam in Action
http://mojavelinux.com
http://mojavelinux.com/seaminaction
NOTE: While I make a strong effort to keep up with my email on a daily
basis, personal or other work matters can sometimes keep me away
from my email. If you contact me, but don't hear back for more than a week,
it is very likely that I am excessively backlogged or the message was
caught in the spam filters. Please don't hesitate to resend a message if
you feel that it did not reach my attention.
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