Dry way to validate custom form fields

Hello 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:

params[:range_count_from] params[:range_count_to] params[:range_pre_text] params[:range_post_text]

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?

/MartOn

Nobody with a good example for me?