Validating non-model forms - a predicament

Patrick L. wrote:

But when the model is saved, the :card and :expiration_date fields are
not validated because they're not part of the model (they are accessed
using params[:cc][:card] and params[:cc][:expiration_date]).

Add them as attributes to the model and then create validation rules as normal -

attr_accessible :expiration_date

validates_presence_of :expiration_date