[Zope] ZClass "add" question

[David Salgado]

>along with some information about an image.  If the user does not specify 
>an image file, I don't want to add a new ZClass instance which would hold 
>information about the image.  In my add method, I've tried doing something 

Why not put some JavaScript validation code in the 'calling form' page which
sets a hidden form variable (e.g. 'CreateInstance') to true iff the the
'photoFile' field is not empty?

HTH

             David