mojavelinux.com: Open Source Advocacy

Great tip. Now if you'll excuse me I'm off to check all my code...

Hi,

I think there's a mistake in the last block of code:

At the end of the first line when you use the value attribute. I think that it's value = "#userList.users"

I'm quite sure that what I have in the <h:dataTable> is correct. A value expression is written as #{userList.users}.

This article it is great clue. However, I'm scared because my application uses this approach, which was recomended on the book Jboss Seam (Michael Juan) as "...avoid excesive bijection" because it is slow. My application uses long running conversations, and nested conversations intensively, and have noted queries being performed several times. However, starting a use case with a long running conversation, and then keeping nested conversations has solved this problem.

Since I'm new to Seam, i'd like to have your opinion.

Thank you.

@Roger, I'm pretty sure that Michael recommended the factory approach in his book JBoss Seam, based on what I see in the source code.

As @Roger pointed out, an alternative solution is to start a long running conversation and then store the data (in this case a list) in the conversation context. The main point here is that the retrieval of the data should be separated from the access of the data. You shouldn't care how many times JSF decides to ask for the data, as long as there isn't a direct channel to the database.

@Pierre Deruel imho your question is valid, as I assume you're talking about the following line <h:dataTable id="users" var="user" value="#{users}">

the expression #{users} could come from the value property of the @Factory annotation @Factory(value = "users" ..

Either way, great point by Dan, and another reason of considering seam.

@cvl Yes, that is the proper explanation. Perhaps @Pierre didn't realize that the #{users} expression is being supplied by the @Factory annotation. Perfectly understandable if you aren't familiar with Seam.

If you want to know the ins and outs of Seam, I promise you that if you read Seam in Action, you won't be let down.

In your solution you say that you should use the factory component delivered by Seam. But this approach is framework dependent (here seam) and can't be used in every application.

Maybe the simplest solution to avoid multipe db queries is to save your list in your bean and only if the list is null perform a db query (works well for request scoped beans).

public class UserListBean {
    private UserService userService;
    prviate List users;
    public List getUsers() {
        if(users == null){
            users = userService.findAll();
        }
        return users;
    }
}

ok, ugly code.. With JSF 1.2 it is possible to use @PostConstruct annotation to initialise your list.

public class UserListBean {
    private UserService userService;
    prviate List users;
    @PostConstruct
    public void init() {
        users = userService.findAll();
    }
    public List getUsers() {
        return users;
    }
}

I think the real problem lies in the understanding how JSF works and that getters will be called not only once per page. Thus you should not perform db actions or do anything else in your getter methods.

But i do agree that with the Seam factory component there exist a quite good answer for this problem. Without Seam you have to search for an other solution.

@Markus, yes, I will grant you that the first solution does indeed work, but I purposely didn't mention it because I find it to be extremely ugly. I do, however, like the second solution. That's a good suggestion. It relies on JSF 1.2, but then again, so does Seam.

Personally, I think its crazy not to use Seam when using JSF, and even crazier to use JSF 1.1. That is my opinion, though.

What if I don't use Seam? Can I still have only JSF solution to overcome this problem?

You can solve this problem in JSF by simply caching the result of the lookup in a property on the object and performing a null check before looking up a value. You can see an example of this in comment #8.

I like @Factory approach , but i think it is necessary to its evolution to take account of paging data very large. I immagine an @Factory(int totalNumRows, int pageSize) that loads only the data of the current page. Actually i use this solution: http://wiki.apache.org/myfaces/WorkingWithLargeTables

best regards

Fiorenzo

About comments #8, code portion below:

public class UserListBean { private UserService userService; prviate List users; public List getUsers() { if(users == null){ users = userService.findAll(); } return users; } }

Why did you call this an 'ugly code'? Any specific reason? Do you mean that you should not write logic in getter method? Is that any specification? Clarify please.

... Chisty

The code is ugly because it has to be repeated throughout your code base, calling out for a framework feature to prevent the repetition (DRY). You are having to check for null because you are unsure when the method will be called the first time (hence no way to initialize the data ahead of time).

And yes, in practice I generally don't like to put initialization logic in getter methods, but that is more of a personal choice.

Yes, thanks. I get your point.

My last question is: about your post, is there any good solution to this without using SEAM (i.e. if I don't use SEAM but still using JSF and fall into the 'trap')? I'm asking this because my current development combination are JSF with Spring and Hibernate.

Thanks, ... Chisty

I would recommend looking into the Spring Faces project. Perhaps they have a solution. I'm not familiar with it, though.

Btw, Web Beans will have an even more elegant solution to this problem with producer methods, for those following this thread. Though producer methods and factories are equally as effective.

i got one problem regarding jsf seam session , can you please look into this , i am very new to this topic , could you be able to help me , below is my bean package com.gms_v6.model;

import java.util.Date; import java.util.HashSet; import java.util.Set; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.FetchType; import javax.persistence.GeneratedValue; import javax.persistence.Id; import javax.persistence.JoinColumn; import javax.persistence.ManyToOne; import javax.persistence.OneToMany; import javax.persistence.Table; import javax.persistence.Temporal; import javax.persistence.TemporalType; import org.hibernate.validator.Length; import org.hibernate.validator.NotNull; import javax.servlet.http.HttpSession; import javax.faces.context.FacesContext; @Entity public class PatHeader implements java.io.Serializable {

/* FacesContext fCtx; HttpSession session;*/ private Integer patId; /* auto incremented in database */ private String patFirstName; private String patMiddleName;

public PatHeader() { } @Id @GeneratedValue @Column() public Integer getPatId() { /* fCtx = FacesContext.getCurrentInstance(); session = (HttpSession) fCtx.getExternalContext().getSession(false); session.setAttribute("patId", patId); System.out.print(" patId >>>>>>>>> : "+patId);*/ return this.patId; } public void setPatId(Integer patId) { System.out.print(" patId >>>>>>>>> : "+patId); this.patId = patId; }

@Column() public String getPatFirstName() { return this.patFirstName; } public void setPatFirstName(String patFirstName) { this.patFirstName = patFirstName; } @Column() public String getPatMiddleName() { return this.patMiddleName; } public void setPatMiddleName(String patMiddleName) { this.patMiddleName = patMiddleName; }

in the above java class i want put only " patId " into session not other variables how can i do this in jsf seam framework , How will i access this session value in another bean i am using netbeans IDE any help will be great

I am trying to use tomahawk t:dataScroller for pagination on my jsf page. Data is rendered properly for the first page but whenever I try to click any button to go to next page, java script error is thrown as below

form is undefined var oldTarget = form.target;

Any solution to this will be quite helpful.

I am using tomahawk12-1.1.9 lib with JSF2.0