How to make this root path as follows: '/ dashboard' instead of http://example.com ?
root :to => 'dashboard#index', :constraints => lambda{|req| !req.session[:user_id].blank?}
You can accomplish this with:
root :to => redirect('/dashboard') match '/dashboard', :to => "dashboard#index", :constraints => lambda {|req| !req.session[:user_id].blank? }