ruby model controller object oriented design

I have implemented a Paypoint payment into a project I am working on and in the pass I used a class called by a controller to process the payment and act on the response, now i've redone this to process the payment on the before_create callback so that if the payment fails the transction rolls back and I add an error to the model and now the controller code if just checks if the model is save

old controller code

def create
 @model = Model.new(params[:xxx])
 if @model.valid?
    if PayPointPayment.authorise_payment(@model)
      redirect_to new_step
    else
  开发者_如何学C     render :new
  else
    render :new
end

new controller code

def create
    @model = Model.new(params[:xxx])
    if @model.save
        redirect_to next_step
    else
        render :new
end

new model code

class Model
    before_create :process_payment

    def process_payment
        if PayPointPayment.authorise_payment(self)
            return true
        else
            <add errors>
            return false
    end
end

just wondering what the thoughts are on this kind of design is it good or bad or just plain wrong

Rather than performing the payment via before_create it may make more sense to run the payment as part of validation. It might wind up working identically, but the message it sends to the programmer is that validation is a series of requirements that must be met before the model object can be saved, and before_create might take care of pre-requisites that need to be performed to allow creating the end model.

Also, if you ever update the model object, it may change the model enough to require revalidation, but before_create won't catch that.

Compared against your original mechanism, of course, this is probably a huge improvement in almost every respect -- it would allow your model to be used outside of the original controller without giving away product/content to users who haven't paid. (Say, if you expose a SOAP or XMLRPC or email or REST interface that doesn't run through your controller.)