合并两个ActiveRecord数组并按创建的顺序排序

books = Book.find(:all)
articles = Articles.find(:all)

http://guides.rubyonrails.org/layouts_and_rendering.html 我知道我可以这样做:

<%= render :partial => [customer1, employee1, customer2, employee2] %>

materials = books + articles
materials.sort_by_created_at

在视图中:

<%= render :partial => materials %>

如何合并和排序两个ActiveRecord数组???谢谢你的帮助!