application_helper.rb

module ApplicationHelper

	def link_to_add_fields(name, f, association)
    	new_object = f.object.send(association).klass.new
    	id = new_object.object_id
	    fields = f.fields_for(association, new_object, child_index: id) do |builder|
	      render(association.to_s.singularize + "_fields", f: builder)
	    end
    	link_to(name, '#', class: "add_fields btn btn-primary", data: {id: id, fields: fields.gsub("\n", "")})
	end

end