User-centric Routing in Rails 3
Have you ever noticed that the GitHub homepage is different once you log in? I’m not talking about little changes here and there. It’s a completely different page. I have no idea how GitHub does this but I’ll venture a guess and demonstrate how to achieve the same effect.
Update: How to write user-centric routes in Rails 2
There are several common ways to pull this off but many miss the mark.
In the View
Switching content based on the current user is easy enough in the view. After all, current_user is available in the view so why not?
<% if current_user %>
Welcome back, <%= current_user.name %>!
<% else %>
<%= link_to "Learn about us!", about_path %>
<% end %>
But this falls apart when more user-specific information is needed in the view. In the case of GitHub’s user homepage, a lot of extra information (repositories, activity, etc.) is included. This information should be loaded up in the controller. So maybe that’s where the content switch belongs.
In the Controller
With the content switch in the controller, an action might look like this:
def home
if current_user
@feed_entries = current_user.feed_entries
render :private_home
else
render :public_home
end
end
This too feels just a little bit… off. The responsibility of a controller action is to load a dataset from the models and to render a template from the views. So if, depending on whether a user is logged in, an action loads up one of two datasets and renders one of two templates, shouldn’t that action be split into two actions? The question, then, is where do we switch between two actions?
In the Routes!
If you think about it, we do this all the time with REST. The same resource route can map to multiple actions depending the request’s HTTP method. A homepage could be mapped to two actions with:
root :to => "users#show", :via => :get
root :to => "users#create", :via => :post
But how can the routes access whether a user is logged in?
Rails has had routing constraints for some time but Rails 3 introduced request-based and advanced constraints. An advanced constraint is a custom object with a matches? method that receives the request as an argument.
In this case, I’m storing a unique user token in the cookies when a user is logged in. So in lib/logged_in_constraint.rb, I can write my constraint class to check for that token:
class LoggedInConstraint < Struct.new(:value)
def matches?(request)
request.cookies.key?("user_token") == value
end
end
I also need to require the new constraint in config/routes.rb:
require File.expand_path("../../lib/logged_in_constraint", __FILE__)
The Fun Part
Now I can write my two new, GitHub-style homepage routes:
root :to => "static#home", :constraints => LoggedInConstraint.new(false)
root :to => "users#show", :constraints => LoggedInConstraint.new(true)
And that’s it! Give it a shot.
This is just one application of the new Rails 3 request-based constraints and there is no shortage of other fun and interesting applications:
root :to => "static#welcome_to_holland", :constraints => GeolocationConstraint.new("Holland, Michigan")
root :to => "static#visit_holland"
Enjoy!
Comments
I tried to follow this but when I launch “rails s”, I get “uninitialized constant LoggedInConstraintn (NameError)”
wouldn’t it now be possible to open firebug/ developer tools, set a cookie with JavaScript and trick the app?
Stephen: Good catch! My application includes lib in its autoload_paths. Otherwise, the lib/logged_in_constraint.rb file should be required in your routes. Post updated!
Mike: Absolutely. This technique is meant only for smart routing, not secure authentication. If a cookie were forged, your authentication system should handle that in your users#show action.
just seems like a lot of baggage for what is basically
def index user_signed_in? ? _public : _private end
@Mike that works for a couple actions, but breaks down quickly when you have a number of them. Your example only renders views, and quite often your meaty actions will grow a lot larger when you support multiple user roles. Steve’s strategy is a lot more versatile than just an if/else.
Not directly related, but somewhat relevant: this is how I do the same thing with Devise & Warden:
root :to => “users#dashboard”, :constraints => lambda { |r| r.env[“warden”].authenticate? } root :to => “home#index”
@Evan Nice! I didn’t know you could pass a lambda to :constraints. A lot cleaner.
@Evan
That is a great solution and really clean. The only problem that I have with a lot of these solutions is that it really puts a lot of logic in routes.rb, whereas Steve’s solution keeps the logic separate.
Very well done, Thanks for sharing this.
There’s something wrong about the JS for this page. I think too many events are fired when the content is scrolled up and down and as such it’s very sluggish.
I might be beiatng a dead horse, but thank you for posting this!
This appears to be broken as of Rails 3.1.rc4. I get No route matches [GET] “/” when I add the constraint. Laaame.
With Devise, same thing can be achieved with
match ‘/dashboard’, :to => ‘User#dashboard’, :as => :user_root
For those of you using sessions instead of cookies, you can access
request.session[:your_key]
in a proc
I’m using omniauth with the identity strategy, and had to somewhat change the match? method with so it’s contents looks like this:
request.env[“rack.session”].key?(“user_id”) == value
Thanks a lot for sharing. I build a constraint exactly like yours following your blog. It runs great in development, but when I run autotest, there’s a error raised: TypeError: superclass mismatch for class LoggedInConstraint
Do you happen to know that? Thank you very much!
@Larry, superclass mismatches occur when you try to open or define a class that’s already been defined with a different superclass. Because it’s only happening in your tests, you’re probably extending your constraint class in a test support file without properly specifying its superclass. Rather than opening the class, you could instead:
or:
@Steve, Thanks for your responds Steve. I am still confused, I didn’t write any test for class LoggedInConstraint in rspec. In whole projects there’s only in lib/ and in config/routes where LoggedInConstraint appears. Is there other causes to this problem? or…maybe I take your reply in a wrong way?
Just integrated this into our app. Much appreciated guys :)
This was very helpful - thanks!
hi, am i need to write a Struct.rb class too, it is giving me wrong no.of arguments error.
Rails 4 ain’t so hot on this technique, it complains that i’ve defined root twice
This technique works fine in Rails 4 but you need to add one thing. Rails 4 will complain that there are two root_paths. So just take one of them (I usually use the static landing page) and add ‘as: :landing’ to the end of it in routes.
So something like:
root :to => “static#home”, as: :landing, :constraints => LoggedInConstraint.new(false) root :to => “users#show”, :constraints => LoggedInConstraint.new(true)