I couldn't believe it, so I made an example. And I had to discover that
it is true:
org.apache.tapestry.ioc.internal.util.TapestryException
The template for component example.recursive.components.Node is
recursive (contains another direct or indirect reference to component
example.recursive.components.Node). This is not supported (components
may not contain themselves).
I consider this a bug that has to do with the alpha state of T5.
Otherwise I have doubts on the usefulness of T5 at all.
Todd Orr wrote:
> I'm also trying to perform this type of recursive structure. I don't
> agree that this makes anything simpler. Recursion is a powerful and
> concise tool for these situations. I will say that it is often abused,
> but this is a perfect use case. A recursive solution to this problem
> is far simpler and maybe more "correct" than this iterative approach.
>
> First off, the proposed solution requires complicated logic. Fine,
> it's not rocket science, but the recursive alternative (if there was
> one in tap) is far easier to read and understand. From a
> tech-management point of view the simplicity of the code is a major
> factor in its long term maintainability as well as its bugginess.
>
> Secondly, the proposed solution requires adding raw HTML output to
> code. This may be a more esoteric and arguable point, but Tapestry
> excels in having a clear and easy to use separation between the
> view/presentation and the logic components of the application's
> construction. Again, with regards to maintainability, it is twice as
> hard to maintain code if the concerns are spread throughout
> conceptually separate pieces of code.
>
> Third, this approach makes it impossible for any "node" in the tree to
> contain any non-trivial nested components. I see that you can create
> links...wow. Kinda limiting if you ask me. This limits the usefulness
> and extendability of the code. If more complex functionality is
> required (lets say by a major client or some other critical business
> need) within this pseudo-recursive implementation it might force the
> developers to completely switch out frameworks to one more suitable
> for the job. This is a huge risk from a business perspective.
>
> While I think these points are painful enough on their own, it does
> raise some questions about the framework's usefulness in specific
> situations. My main concern is in relation to CMS features. Many
> applications require support for some level of features that would be
> considered CMS functionality. This static structure imposed makes
> creating dynamic sites, well, painful. When you are attempting to
> build an application that must adapt to known types of "runtime" or
> user-configuration driven alterations that have many variants during
> runtime (eg. depth of a tree, etc.) the static structure is limiting.
>
> Tapestry is a great framework. However, the intention of the static
> structure, while clearly advantageous in many respects, limits the use
> case coverage for the framework at worst and makes certain otherwise
> easy tasks very difficult at best.
>
> Perhaps the rules for the static structure could be allowed to bend
> from time to time as a nod to those of us that do require greater
> flexibility. I'm sure this is easier suggested than done, but what are
> the options?
>
> On 7/17/07, Francois Armand <[EMAIL PROTECTED]> wrote:
>
>> Dmitry Sidorenko wrote:
>>
>>> Hi all.
>>>
>>>
>> Hi,
>>
>>
>>> In my project I need to generate edit form for a class like this:
>>>
>>> class Section{
>>> List<Section> subSectionList;
>>> List<Field> fieldList;
>>> }
>>>
>> > [...]
>>
>>> Probably I'm doing something wrong, maybe my task should be done in
>>> completely different manner.. Any ideas?
>>> Is there any way to develop visual editor for such a recursive classes?
>>>
>> I don't know how T4 works, but if it's like in T5, their is no support
>> of recursive template/class.
>> So, for tree structure, you have to use a non-recursive algorithm (I
>> think that in your example, you wish to use a non-recursive preorder
>> traversal).
>> It's not really natural, but the non-support of recursive structure
>> seems to bring a lots of simplification with it.
>>
>> You can look at this How To entry :
>> http://wiki.apache.org/tapestry/Tapestry5HowToCreateYourOwnComponents
>>
>>
>> I wish it would help.
>>
>> Francois
>>
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