carrierwave simple validation

subject.rb

class Subject < ActiveRecord::Base
  mount_uploader :icon, IconUploader

  validates_presence_of :icon
  validate :image_size_validation, :image_type_validation, :if => "icon?"


  def image_size_validation
    errors[:icon] << "should be less than 2MB" if icon.size > 2.megabytes
  end

  def image_type_validation
   errors[:icon] << "should be .jpg or .png file format" if (/(jpeg|jpg|png)/ =~ icon.file.content_type).nil?
 end

end