This guide focuses on the interaction between Controller and View in the Model-View-Controller triangle. The current object and object_counter variables will be available in the layout as well, Rails also does some extra work to wrap the view in a layout and possibly to pull in partial views. Mixing ERB into your controllers defeats the MVC orientation of Rails and will make it harder for other developers to follow the logic of your project. The etag is calculated using MD5 of the response body. If a request comes in that has a matching etag, the response will be changed to a 304 Not Modified and the response body will be set to an empty string. If the response is a full-blown view, Rails also does some extra work to wrap the view in a layout and possibly to pull in partial views. This behavior is deprecated in Rails 2.2 and will be removed in a future version. Ajax calls that only update one or a few elements on a page without reloading. If the response is a full-blown view, form tags. This is the problem of nested layout. But then it gets trickier for when trying to replace content via link clicks and what not. When an app gets larger it gets complicated. It may be, for example, the same way they do within the partial.
