Seam's improvement

[alpha88]

Hi,

I have some improvements about Seam. See the following:

// import statements

@Stateless
@Name("messageService")
public class MessageServiceImpl implements MessageService {

    @PersistenceContext
    private EntityManager em;

    // equals signal omitted
    @DataModel(scope=ScopeType.PAGE)
    private List<Message> messageList;

    @DataModelSelection
    @Out(required=false)
    private Message selectedMessage;

    public void getMessage(Integer messageId) {
        selectedMessage = em.find(Message.class, messageId);
    }

    public void getMessage() {
        // selectedMessage has been retrieved through @DataModelSelection, so no action is needed
        return;
    }

    @Factory("messageList")
    public void getAllMessage() {
        messageList = em.createQuery("from Message m order by m.info asc").getResultList();
    }
   
}

If i have requested a getAllMessage.seam as follow:

<h:form>
    // throws @Factory("messageList") and fills out @DataModel messageList in MessageServiceImpl
    <h:dataTable value="#{messageList}" var="_message">
        <h:column>
            #{_message.info}
        </h:column>
        <h:column>
            <s:link value="#{_message.info}" action="#{messageService.getMessage}"/>
        </h:column>
        <h:column>
            <h:commandLink value="#{_message.info}" action="#{messageService.getMessage(_message.id)}"/>
        </h:column>
    </h:dataTable>
</h:form>

See the code above: why do i use "s:link" when the action is getMessage and "h:commandLink" when the action is getMessage(_message.id) ?

Answer is found in MessageServiceImpl:

@DataModelSelection(scope=ScopeType.PAGE)
private List<Message> messageList;

ScopeType.PAGE says: remember my state at next postback OR save my state in the JSF UI tree. Ok. It happens "s:link" does not work if state is stored at JST UI tree. "h:commandLink" does. By the way, "h:commandLink" needs to be inserted inside a "h:form"; "s:link" does not; So, the postback needs remember which _message has been selected when you call "action=#{messageService.getMessage(_message.id)}". "h:commandLink" fulfill this requirement. If you use a "s:link" then you must call "action=#{messageService.getMessage}" with no arguments and use a @DataModelSelection to gain access to message selected in @DataModel.

Ok, let's go. So, what's the problem ?

first: if you use a getMessage method, what comes in mind ? here the answer: which message ? So we need a parameter, often a id in order to retrieve the requested message. Because "s:link" does not allows to pass parameters whether we use a @DataModel in PAGE scope, we have to adapt our getMessage with no arguments in order to use "s:link" because seam does not provide this funcionality.

What i suggest ? Something like this:

A "action" tag nested a "s:link" that support simple Java types - primitives and Wrappers

<s:link>
    <action method="getMessage">
        <param>#{_message.id}</param>
    </action>
</s:link>

It will throws getMessage(Integer id)

It could be use a JSF converter like this one

<s:link>
    <action method="#{messageService.getMessage}">
        <param converterType="javax.faces.convert.IntegerConverter">#{_message.id}</param>
    </action>
</s:link>

Or allows multiple simple Java Types parameters like this one whether we use a composite id

<s:link>
    <action method="#{messageService.getMessage}">
        <param converterType="javax.faces.convert.IntegerConverter">#{_message.id1}</param>
        <param converterType="javax.faces.convert.IntegerConverter">#{_message.id2}</param>
        <param converterType="javax.faces.convert.IntegerConverter">#{_message.id3}</param>
    </action>
</s:link>

It will throw getMessage(Integer id1, Integer id2, Integer id3)

Cool, don't. This way we do not have to put @DataModel in PAGE scope. We could simply put it in a EVENT scope, which is lighter.

Now, let's consider the following scenario: we have removed the @DataModel and @DataModelSelection. Again, there is another approach to @Factory method as follows

// ATT: @DataModel can not be marked in method
@Factory("messageList")
public List<Message> getMessageList() {
    return em.createQuery("from Message m order by m.info asc").getResultList();
}

Notice that getMessageList returns a List<Message> (opposed to void in previous example). This way, we cannot use <h:dataTable because @Factory method has been not encapsulated in a @DataModel as follows

// It does not work. Factory method needs to be encapsuled in a @DataModel.
<h:dataTable value="#{messageList}" var="_message">

What's the solution ?

// ui facelets
<ui:repeat var="_message" value="#{messageList}">
    #{message.info}
</ui:repeat>

With param tag, as propposed, we could be use as follows, even whether our MessageServiceImpl does not contain a @DataModel and @DataModelSelection:

<ui:repeat var="_message" value="#{messageList}">
    <p>
        <s:link value="#{message.info}">
           <action method="#{messageService.getMessage}">
               <param>#{_message.id}</param>
           </action>
        </s:link>
    </p>
</ui:repeat>

ATT: as we have left @DataModel behind, we can not use something like this

<s:link action="#{messageService.getMessage}" because neither @DataTable nor @DataModelSelection lives in MessageServiceImpl anymore.

Regards,
Arthur Ronald F D Garcia - Java programmer
(Natal - Brazil)