validation question

rubyonrails-talk
1

I have a courses model that has two fields:

courses(title, members_count)

Is it possible to have a validation that only lets the user update the title if members_count == 0?

def validate   errors.add(:title, "cannot be changed once users have signed up") if members_count > 0 and title_changed end

But I'm not sure how to check that the title has changed - any help is appreciated. Thanks!

2

I've never liked the solutions I've come up with... but from a practical perspective you might simply disable the text_field if member_count>0.

3

Create a hidden field old_title. You'll need to add an attr_accessor, but then you should be able to check if old_title == title. But I liked the other suggestion better... why have the text field if it can't be changed? Perhaps you should render a partial that only shows the enabled text field if member_count<0

-Ryan

4

I thought about something like that, but I think it would fairly easy to bypass - all the user would need to do is change the form and submit it to change the title regardless of members_count. Any other ideas? My guess is that this is a fairly common type of validation people need to perform...

5

I got something that works by saving the previous title from the controller:

  def update     @course = Course.find params[:id]     @course.save_previous_title     @course.attributes = params[:course]     @course.save!     flash[:notice] = "Class #{@course.title} updated"     redirect_to_course   rescue ActiveRecord::RecordInvalid     render :action => :new   end

and in models/course.rb

  attr_accessor :previous_title   def save_previous_title     self.previous_title = title   end

  def validate    errors.add(:title, "cannot be changed once users have signed up") if members_count > 0 and title != previous_title   end

It doesn't feel very clean though - anyone know if I can set a callback to save_previous_title in the model before it updates itself so I don't have to call it explicitly from the controller or if there is a better way to go about this?