Shared errors for multiple targets (when you need render errors for a form containing nested or unlinked )

application_helper.rb

  def collect_shared_error_messages(target)
    targets = []
    error_messages = []
    if target.kind_of?(Array)
      target.collect {|t| targets << t}
    else
      targets << target
    end
    targets.each do |target|
      target.errors.full_messages.collect {|msg| error_messages << msg} if target.errors.any?
    end
    error_messages
  end

error_messages.html.haml

- error_messages = collect_shared_error_messages(target)
- if error_messages.any?
  #error_explanation
    %h2= "#{pluralize(error_messages.count, "error")} prohibited this record from being saved:"
    %ul
      - error_messages.each do |msg|
        %li= msg

view_with_form.html.haml

      = form_for @something do |f|
        = render "shared/error_messages", :target => [@something, @something.else]
        # ... your fields