Refactoring repeated custom validation in Rails

Question

I have a custom validation which is repeated multiple models. Is there a way to refactor it and make it dry?

class Channel < ActiveRecord::Base

  belongs_to :bmc
  has_and_belongs_to_many :customer_segments

  validates :name, presence: true
  validate :require_at_least_one_customer_segment

  private

  def require_at_least_one_customer_segment
    if customer_segments.count == 0
      errors.add_to_base "Please select at least one customer segment"
    end
  end

end



class CostStructure < ActiveRecord::Base

  belongs_to :bmc
  has_and_belongs_to_many :customer_segments

  validates :name, presence: true
  validate :require_at_least_one_customer_segment

  private

  def require_at_least_one_customer_segment
    if customer_segments.count == 0
      errors.add_to_base "Please select at least one customer segment"
    end
  end
end

 class CustomerSegment < ActiveRecord::Base
   has_and_belongs_to_many :channels
   has_and_belongs_to_many :cost_structures
 end

Any reference link also much appreciated.Thanks!!

Answer 1

Try using concerns:

app/models/concerns/shared_validations.rb

module SharedValidations
  extend ActiveSupport::Concern
  include ActiveModel::Validations

  included do 
    belongs_to :bmc
    has_and_belongs_to_many :customer_segments

    validates :name, presence: true
    validate :require_at_least_one_customer_segment
  end
end

then in your classes:

class CostStructure < ActiveRecord::Base
    include Validateable
end