custom validation for 1 attr

class EmailUniquenessValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)  
    user = User::Account.find_by_email(value)
 
    if user != nil
      record.errors.add(:base, I18n.t('user.webview.sign_up_error_msg')) # base errors are not specific to any attribute so it's not appended 
      return false
    end
 
  end
end
 
 
class User::Account < User::User
     validates :email, :email_uniqueness => true
end