[html-formfu] Validator vs Constraint

[Andreas Marienborg]

On Mar 13, 2008, at 10:49 AM, Carl Franks wrote:

> On 06/03/2008, Andreas Marienborg <omega at palle.net> wrote:
>> To follow up even further, what is the rationale behind validators
>> only running if all constraints pass? It makes for a rather
>> unintuitive process for the users? They get 3 red boxes, fix them,  
>> and
>> _then_ get another red box on something that seemed fine.
>>
>> I can understand validators only running for fields where constraints
>> pass, but only after all seems a bit strange.
>
> I originally made each step (constraints, inflators, validators,
> transformers) an "all or nothing" effort because:
> - firstly for inflators - they could be considered relatively
> expensive, and so if there's any constraint errors on *any* fields,
> you'll probably just be re-displaying the form again, and so probably
> wouldn't want any inflators run.
> - validators - I originally thought would be used for higher-level
> "business logic" involving multiple fields. If you're needing to
> validate on a single field, and it doesn't need inflated - then you
> may be as well using a Constraint instead.
>
> If you wanted validators to run if there's constraint errors on
> unrelated fields, there would need to be a mechanism for the validator
> to state which other fields should also be error-free (much like
> others() on some constraints).
> I think this would probably be a bit too much complexity, and error
> prone, as the field list would need to be kept in sync with the
> validation code.
>
> Currently the only validator is HTML::FormFu::Validator::Imager::Size.
> I've never yet needed to write any custom validators.
>
> I hope this explains how we got where we are :)

Then may I suggest rewording the documentation?

"Validators are intended for higher-level validation, such as business- 
logic and database constraints such as "is this username unique?"."

Which is exactly what I had in a Constraint, until I read that section  
and figured it should probably be a Validator instead.

I'll just goahead and change my validators back to Constraints again  
then :)

thanks for the response!


- andreas