Ruby on Rails choosing wrong controller action

Question

Today I came across some strange (and very inconvenient) Ruby on Rails behavior that even persistent combing of the net did not yield a satisfying answer to. Note: I translated the method and route names to be easier to read in English, and hope I did not introduce any inconsistencies.

Situation

Environment

Ruby on Rails 4.2.0 executing under Ruby 2.0 (also tested under Ruby 2.2.0)

Relevant Code

consider a controller with these actions, among others:

class AssignmentsController < ApplicationController
  def update
    ...
  end

  def takeover_confirmation
    ...
  end
end

routes.rb

Since I use a lot of manually defined routes, I did not use resources in routes.rb. The routes in question are defined as follows:

...
post 'assignments/:id' => 'assignments#update', as: 'assignment'
post 'assignments/takeover_confirmation' => 'assignments#takeover_confirmation'
...

The relevant output of rake routes:

assignment POST  /assignments/:id(.:format)  assignments#update
assignments_takeover_confirmation  POST  /assignments/takeover_confirmation(.:format) assignments#takeover_confirmation

Problem

When I do a POST to the assignments_takeover_confirmation_path, rails routes it to the update method instead. Server log:

Started POST "/assignments/takeover_confirmation" for ::1 at ...
Processing by AssignmentsController#update as HTML

Mitigation

If I put the update route definition after the takeover_confirmation one, it works as intended (didn't check a POST to update though).

Furthermore, after writing all this I found out I used the wrong request type for the update method in routes.rb (POST instead of PATCH). Doing this in routes.rb does indeed solve my problem:

patch 'assignments/:id' => 'assignments#update', as: 'assignment'

However, even when defining it as POST, Rails should not direct a POST request to the existing path "/assignments/takeover_confirmation" to a completely different action, should it? I fear the next time I use two POST routes for the same controller it will do the same thing again.

It seems I have a severe misconception of Rails routing, but cannot lay my finger on it...

Edit: Solution

As katafrakt explained, the above request to /assignments/takeover_confirmation matched the route assignments/:id because Rails interpreted the "takeover_confirmation" part as string and used it for the :id parameter. Thus, this is perfectly expected behavior.

Working Example

For the sake of completeness, here is a working (if minimalistic) route-definition that does as it should, inspired by Chris's comment:

  resources :assignments do
    collection do
      post 'takeover_confirmation'
    end
  end

In this example, only my manually created route is explicitly defined. The routes for update, show, etc. (that I defined manually at first) are now implicitly defined by resources: :assignments.

Corresponding excerpt from rake routes:

...
takeover_confirmation_assignments  POST  /assignments/takeover_confirmation(.:format) assignments#takeover_confirmation
...
assignment GET    /assignments/:id(.:format)  assignments#show
           PATCH  /assignments/:id(.:format)  assignments#update
           PUT    /assignments/:id(.:format)  assignments#update
           DELETE /assignments/:id(.:format)  assignments#destroy
....

Thanks for the help!

Answer 1

However, even when defining it as POST, Rails should not direct a POST request to the existing path "/assignments/takeover_confirmation" to a completely different action, should it?

It should. Rails routing is matched in exact same order as defined in routes.rb file (from top to bottom). So if it matches a certain rule (and /assignments/takeover_confirmation matches assignments/:id rule) it stops processing the routing.

This behaviour is simple and efficient. I imagine that any kind of "smart" matching the best route would result in cumbersome and unexpected results.

BTW that's why catch-all route used to be defined at the very bottom of routing file.