[Seaside-dev] Pier/Magritte Dynamic Descriptions

[Joel Kitching]

Recently I was trying to puzzle out how to provide some descriptions on 
some objects that changed based on other descriptions.

A concrete example of this is: a Flickr photo, with two descriptions:
- photo ID
- which JPG size to use

The second description depends on the first -- one can't retrieve the 
available sizes to choose from without first getting the photo ID.

So I did a bit of Googling around, and came across an On Smalltalk [1] 
article, where it mentioned something about this:

> Generally speaking you'll keep these descriptions on the class side of
> your domain object. On occasion, you'll want some property of the
> description to be dynamic and depend on the actual value of an instance
> side value, so you'll move the description to the instance side.
> Strictly speaking, it doesn't matter where you put them, sometimes
> you'll use them to build forms when you don't even have a domain object,
> but this isn't the normal case.

Then I did some further looking, and found some tutorial [2] that 
actually gives some information on doing this (without Pier).  It seems 
like in general (based on this tutorial) you implement #descriptionEdit, 
and then grab that when handling the editing function in whatever UI you 
choose.

That said, I've been struggling to figure out how I can do this with a 
PRWidget in Pier.  There seems to be some way of doing it with a 
PRStructure, as PRFile provides editing capabilities on a text-based 
file by overriding #editDescription.  But I'm not sure how it would work 
with a PRWidget, or if it is even possible.

Basically, I would envision it as follows in the UI, continuing with the 
Flickr photo example:
- Create a new photo widget
- Edit the photo widget -- the size property either does not show or is 
not populated
- Input a photo ID
- Either submit the form, or have something realize it has what it needs 
to populate the next field and transmit the data without a page refresh
- Select the photo size, and submit

Is there any way of accomplishing this with the existing support for 
Magritte in Pier?  Or is this something that could be (or should be) 
hacked into PRWidget?  Or am I going about this in a completely wrong way?

Any advice would be much appreciated.

Thanks,
Joel

[1] http://onsmalltalk.com/using-magritte-with-seaside
[2] 
http://www.hpi.uni-potsdam.de/hirschfeld/seaside/tutorial?chapter=10#part4