```ruby
Spree::Core::Engine.routes.prepend do

  namespace :admin do

    resources :relation_types
    resources :products do
      get :related, :on => :member
      resources :relations do
      	collection do
        	post :update_positions
    	end
      end
    end
      
  end

end
```

Use draw to avoid mutliple declarations
user
```ruby
Spree::Core::Engine.routes.draw do
  namespace :admin do
    resources :relation_types
    resources :products, only: [] do
      get :related, :on => :member
      resources :relations do
      	collection do
        	post :update_positions
    	end
      end
    end
  end
end
```
assistant