link_to , simple_form_for , two models

link_to  或者是 simple_form_for 後面有時候皆兩個model

• <%= link_to "New Comment", [:new, @commentable, :comment] %></p>
• simple_form_for [@post, @comment]

因此查了一下文件 了解其原理

http://apidock.com/rails/ActionView/Helpers/UrlHelper/link_to

http://apidock.com/rails/ActionController/Base/url_for

http://apidock.com/rails/ActionController/PolymorphicRoutes/polymorphic_url

http://edgeguides.rubyonrails.org/routing.html#creating-paths-and-urls-from-objects