Question

I’m working on my first Rails app. It needs to store some information about a single advertisement that will appear on every page. The admin just needs to be able to set the URL, Title, and an image. Obviously, I only need one instance of this ad object.

I created a model that inherits from ActiveRecod::Base, but that seems like the wrong thing to do, since it is configured to save multiple ads in a database table.

What’s the best way for me to do this? What should the model and controller look like?

Thanks in advance,
Avi

Answer 1

I would suggest that you continue using ActiveRecord but that you add a boolean attribute that determines which of the many advertisement records is the active one. I have called this field active within the following example.

You can then validate within the model that a maximum of one record is active. The validation of the active attribute should succeed under any of the following conditions

1. The active attribute is set to false
2. There are 0 records with an active value of true.
3. The current record already has the attribute set to true in the database.

The following class should meet your needs

class Ad < ActiveRecord::Base

  named_scope :has_active, :conditions => {:active => true}

  def validate
    errors.add_to_base "You can only have one active advertisement" 
        unless self.active_flag_valid?
  end

  def active_flag_valid?
    self.active == false || 
    Ad.has_active.size == 0 || 
    ( Ad.has_active.size == 1 && !self.active_changed?)
  end
end