Simple alert error message helper

application_helper.rb

module ApplicationHelper
  # Renders the first field error of an object attribute on a red alert.
  #
  # @param klass [Class Object] - This object needs to
  # include ActiveModel::Validations (or be a normal ActiveModel)
  # @param field_sym [Symbol] - Attribute or field name of the object
  
  def show_error_message_for(klass, attribute)
    if klass.errors[attribute].any?
      %(
       <div class="alert alert-danger">
        #{klass.errors.full_messages_for(attribute).first}
       </div>
      ).html_safe
    end
  end
end