You could do it in the controller action the form posts to. Or, if
you want to keep your controller skinny you could possibly create a
model not associated with a database table with validation methods and
call object.valid? from the controller but never call object.save You
could alternately create a new class that would validate the form data
but that may or may not take more work on your part. There are a
number of approaches that might work.
Personally, if the validations would be quick and simple (like
checking the length of a field) then I would do it from the
controller, if I knew I would have to use more than, say, 10 lines, or
the validations are non-trivial, I would use a model/class.
If you need a more specific guidance you should possibly paste the
form and provide additional details as to what you're trying to