Adding a validation error with a before_save callback or custom validator?

Question

I have a model Listing that belongs_to :user. Alternatively, User has_many :listings. Each listing has a category field that classifies it (dogs, cats, etc). The User also has a boolean field called is_premium.

Here is how I am validating the category...

validates_format_of :category,
                    :with => /(dogs|cats|birds|tigers|lions|rhinos)/,
                    :message => 'is incorrect'

Let's say I only want to allow premium users to be able to add tigers, lions, and rhinos. How would I go about this? Would it be best to do it in a before_save method?

before_save :premium_check

def premium_check
  # Some type of logic here to see if category is tiger, lion, or rhino.
  # If it is, then check if the user is premium. If it's not, it doesn't matter.
  # If user isn't premium then add an error message.
end

Thanks in advance!

Answer 1

class Listing < ActiveRecord::Base    
  validate :premium_category

  private

  def premium_category
    if !user.is_premium && %w(tigers lions rhinos).include?(category))
      errors.add(:category, "not valid for non premium users")
    end
  end
end

Answer 2

If you want to add validation errors doing the before_save you could raise an exception then add the error in the controller like this:

class Listing < ActiveRecord::Base    
  before_save :premium_category

  private

  def premium_category
    if !user.is_premium && %w(tigers lions rhinos).include?(category))
      raise Exceptions::NotPremiumUser, "not valid for non premium users"
    end
  end
end

Then in your controller do something like:

begin 
    @listing.update(listing_params)
    respond_with(@listing)
rescue Exceptions::NotPremiumUser => e
      @listing.errors.add(:base, e.message)
      respond_with(@listing)    
end

Then in your /lib folder add a class like this:

module Exceptions
  class NotPremiumUser < StandardError; end
end

But in your case I think using the validate method is a better solution.

Cheers,

Answer 3

You can use validates_exclusion_of:

validates :category, :exclusion => {
  :in => ['list', 'of', 'invalid'],
  :message => 'must not be premium category',
  :unless => :user_is_premium?
}

protected

def user_is_premium?
  self.user.premium?
end