Why is the scaffold generating routes like this? Why do they work?

Question

The book "Agile development with Rails" shows in the second chapter, that you can say:

<%= link_to "Goodbye",say_goodbye_path %>

Instead of hardcoding the path to "/say/goodbye". Makes sense, I thought to myself. Probably Ruby is splitting the say_goodbye_path by _, assigns the first part as the controller name, the second part as the action name. But, afterwards, I generated the following scaffold:

rails generate scaffold User name:string mail:string

And I noticed in the index.html.erb view, that it had methods like: edit_user_path(user). I tried to rewrite it to user_edit_path(user), but of course, it didn't work. My question is, why are the scaffold links the other way around? How would I know if I should write them in the way the author uses them in link_to, or in the way they are generated by the scaffold. Can you shed some light on this?

Answer 1

The helper functions like user_edit_path are automatically generated by rails to map operations on resources to the matching routes and thus HTTP paths and HTTP verbs. You have to understand that you are dealing with resources here, not necessarily with simple controllers.

While most of the time your resources can map to a single controller, it doesn't have to be that way. You can have nested or combined resources which can result in rather complex routing definitions.

Resources are typically defined by giving it a name (userin this case) and defining some allowed operations on them. Rails encourages to follow the REST pattern there, so you can have shortcuts to have some operations pre-defined. One of them is edit, which by default matches to a GET request to users_controller#edit. Default operations on RAILS resources are:

HTTP verb  path          matching controller action
===================================================
GET        /users        #=> index
GET        /users/1      #=> show
GET        /users/new    #=> new
GET        /users/1/edit #=> edit
PUT        /users/1      #=> update
POST       /users        #=> create
DELETE     /users/1      #=> destroy

These mappings can be customized on your routes.rb (changing methods, adding or removing operations, ...) Generally you are encouraged to use the default mappings as these are supported by standard helpers and make your app easier to understand.