NoMethodError in UserController#register undefined method `save' for nil:NilClass - ruby-on-rails

Question

Trying to learn ruby on rails following Michael Hartl's tutorial, when I try to go to the registration page in the book I get this:
NoMethodError in UserController#register
undefined method `save' for nil:NilClass
here is the code from the user_controller.rb file:
class UserController < ApplicationController
def index
#title = "RailsSpace User Hub"
end
def register
#title = "Register"
if request.post? and params[:user]
#user = User.new(user_params)
end
if #user.save
flash[:notice] = "User #{#user.screen_name} created!"
redirect_to :action => "index"
end
end
private
def user_params
# Add the user attributes that you sent with post (form) to the permit
method.
params.require(:user).permit(:name, :screen_name)
end
end
It's complaining about line 11 where it says: if #user.save I'm just following the tutorial I don't know what's going on.

Answer 1

Try to understand what the error message is saying. You're trying to call .save on #user but where you are calling it, #user may not be defined. The problem is you can't call .save on a nil object so it throws NoMethodError.
You're logic is incorrect so you must first make sure #user is instantiating a new User instance. It should be more like this:
def register
#title = "Register"
if request.post? && params[:user]
#user = User.new(user_params)
if #user.save
flash[:notice] = "User #{#user.screen_name} created!"
redirect_to :action => "index"
else
# handle erorrs here
flash[:alert] = "Please fix errors: #{#user.errors.full_messages.inspect}"
redirect_to :back #this may need to change depending, just an example.
end
end
end

Answer 2

NoMethodError in UserController#register undefined method 'save' for nil:NilClass
The error is thrown because you are calling save on a nil; and it is because nil object does not have this method. the save is a instance method belonging to ActiveRecord::Base class.
The reason #user is nil is because #user is an instance variable in the UserController class which you have not given it any value. Any variable starting with # inside a class is an instance variable in Ruby.
To solve this problem, you should set a value to #user, and in this case it should be a User instance. You can either create a new user object by doing #user = User.new(user_params) or you fetch a record from the Database by doing #user = User.find(<some_id>)