JSF/Seam -- Nested/Recursive iteration

Question

I've got a situation where I would like to perform nested iterations on a series of options and display the results using JSF. As an example, think of a discussion board. Each comment may contain a parent comment and 0-n child comments. So, my root object would be something like this:

public class MyObject {

...

public List<Comment> getComments();

...
}

And my comments would look like this:

public class Comment {

...

public Comment getParent();

...

public List<Comment> getChildComments();

...
}

I've got all of my entities setup using JPA and they are populated within the database. But, my dilema is, how do I iterate over each comment so I can display its child comments inline? I know I can use <ui:repeat value="#{myObj}" var="comment" /> to iterate over the root-level comments for an object. But, how do I then iterate over the children comments for each of those? And then, how do I iterate over their child comments. And so on, and so on.

Has anyone ever done anything like this? I suppose "Nested Iteration" could really be thought of more as "recursive iteration". Thoughts?

Answer 1

For fixed-size nested iterations, simply use:

<ui:repeat value="#{myObj}" var="comment">
    <ui:repeat value="#{comment}" var="subComment">
        <ui:repeat value="#{subComment}" var="subSubComment">
        </ui:repeat>
    </ui:repeat>
</ui:repeat>

If you want full recursion, fetch the data in some Tree structure in your bean, using whatever loops you like, and use it just for visualization, in a simple iteration. You may need to have a "level" property of the objects that you put in your Tree.