Question

Is there any way I can add a validation to the user model such that usernames that are the same as already defined routes are rejected?

For instance:

get 'search'
get :username => "users#show", :as => :user

If the user enters “search” as the username it would reject it because that already exists as a rails route.

The possible other approach is to create an explicit blacklist, but obviously that requires more maintenance as new routes are added.

Edit

Adapted answer into working solution:

validate :username_blacklist

private
@@username_blacklist = nil

# checks if the username is on a blacklist
def username_blacklist
  unless @@username_blacklist
    @@username_blacklist = Set.new [ "badword", "naughtybadfun"]
    Rails.application.routes.routes.each do |r|
      reserved_word = File.dirname(r.path).split('/')[1]
      @@username_blacklist << reserved_word if reserved_word
    end
  end

  errors.add(:username, "is restricted") if @@username_blacklist.include?(username)
end

Answer 1

In your validation you could loop through all the defined routes and check them against the desired username.

This helps you to get the defined paths:

Rails.application.routes.routes.each {|r| p r.path.to_s}