Dry way to validate custom form fields

I have a controller where I`m implementing a batch/bulk create action
so I can create bulks of items to a model.
The controller have a create_range function where the form sends params
like this:


Is there a simple way to add ActiveRecord kind of validation on them?
For instance the text_field for range_count_from, would like to
validate as a positive Integer.

what is the DRY`est way of doing this.. I would like to have as few If
<statements> as possible..
What is the Rails way of doing this? Should it be handled in controller
or model?


Nobody with a good example for me?