Re: formEncode - complicate validate form

Grzesiek Slusarek wrote:
> Ian Bicking wrote:
> "
> You want a FormValidator, because you are validating pieces 
> together. 
> An example of this is 
> formencode.validators.RequireIfMissing/RequireIfPresent. You 
> might want 
> to look at the implementation; how you use that field is:
> 
> class MySchema(Schema):
>      other fields...
>      chained_validators = [RequireIfPresent(required='birthday', 
> present='i_am_over_18')]
> 
> Form validators validate the entire dictionary that is submitted.
> "
> 
> As I understand in this example both birthday and i_am_over_18 
> are form field. But what if I want to do validate some field of 
> form ONLY if other field has a specific value?
> i saw source of formencode.validators.RequireIfMissing/
> RequireIfPresent and value of field can be achieved by e.g. value
> _dict.get(self.missing) but how called such this validator. 
> This part i don't understand. And is it possible?

A FormValidator validates the entire form at once.  So, maybe:

class RequireIfEqual(FancyValidator):
     # Field name:
     field = None
     # expected value:
     value = None
     other_field = None
     other_validator = None

     def _to_python(self, form, state):
         if form.get(self.field) == self.value:
             conv = self.other_validator.to_python(form.get(self.other), 
state)
             form = form.copy()
             form[self.other_field] = conv
         return form

I think that's roughly what you are describing.