Make semantic_errors render the exact error-message - activeadmin

Question

I have a model Camping which has_many Images. At least one image is required on Camping:
class Camping < ActiveRecord::Base
attr_accessible :images_attributes
has_many :images
validates_presence_of :images, :message => "At least one image is required"
accepts_nested_attributes_for :images, :allow_destroy => true
end
Then, in active_admin, which uses formtastic, I render the error message At least one image is required, with f.semantic_errors:
ActiveAdmin.register Camping do
form :html => { :multipart => true } do |f|
f.semantic_errors :images
#....
f.inputs "Images" do
f.has_many :images do |img|
#....
end
end
#....
end
end
This renders as:
Images At least one image is required.
How can I make it render: At least one image is required?
changing the f.semantic_errors :images into 'f.semantic_errors (removing :images) makes it render nothing; no error at all.
Note: The API documentation seems to imply that Formtastic always adds the :attribute name to the error; but I am not entirely sure how this code works.

Answer 1

If you want to use such custom messages you can add error messages that are related to the object’s state as a whole, instead of being related to a specific attribute
Change this
validates_presence_of :images, :message => "At least one image is required"
to something like
validate :should_have_images
def should_have_images
errors.add(:base, "At least one image is required") if images.blank?
end

Answer 2

If you want to use such custom messages you can add new method to Formtastic::Helpers::ErrorsHelper As follows
create new file at config/initializers/errors_helper.rb
Place following code to file
module Formtastic
module Helpers
module ErrorsHelper
def custom_errors(*args)
return nil if #object.errors.blank?
messages = #object.errors.messages.values.flatten.reject(&:blank?)
html_options = args.extract_options!
html_options[:class] ||= 'errors'
template.content_tag(:ul, html_options) do
messages.map do |message|
template.content_tag(:li, message)
end.join.html_safe
end
end
end
end
end
In activeadmin form use
f.custom_errors instead of f.semantic_errors *f.object.errors.keys