Ruby和Rails：设置current_user if语句

Question

I'm in a controller method.

p current_user
p request.referrer != Rails.application.routes.url_helpers.dashboard_patients_add_url
if request.referrer != Rails.application.routes.url_helpers.dashboard_patients_add_url
  p 'in here'
  current_user = User.find_by_authentication_token(params[:token])[0]
end
p current_user

Returns

#<User id: 33, first_name: "1", last_name: "1", working_at: "1", password_digest: nil, password_confirmation: nil, created_at: "2014-03-20 00:37:54", updated_at: "2014-03-20 00:38:00", email: "aab@gmail.com", encrypted_password: "$2a$10$nw1UHb0PeFUFh17zKRhbsOA.MirNfXW69wj7aRfMSDEw...", reset_password_token: nil, reset_password_sent_at: nil, remember_created_at: nil, sign_in_count: 1, current_sign_in_at: "2014-03-20 00:37:54", last_sign_in_at: "2014-03-20 00:37:54", current_sign_in_ip: "127.0.0.1", last_sign_in_ip: "127.0.0.1", authentication_token: "HHz6KyqrHF7pC41DyGKH", salutation: "1", speciality: "1", cell_phone_number: "1", office_phone_number: "1">
false
nil

So the if statement is false and the p within the if statement is not run...which would lead me to believe that current_user should not get set to the User.find_by_authentication_token result. However, clearly, it does. If I comment out the if statement, then I get

#<User id: 33, first_name: "1", last_name: "1", working_at: "1", password_digest: nil, password_confirmation: nil, created_at: "2014-03-20 00:37:54", updated_at: "2014-03-20 00:38:00", email: "aab@gmail.com", encrypted_password: "$2a$10$nw1UHb0PeFUFh17zKRhbsOA.MirNfXW69wj7aRfMSDEw...", reset_password_token: nil, reset_password_sent_at: nil, remember_created_at: nil, sign_in_count: 1, current_sign_in_at: "2014-03-20 00:37:54", last_sign_in_at: "2014-03-20 00:37:54", current_sign_in_ip: "127.0.0.1", last_sign_in_ip: "127.0.0.1", authentication_token: "HHz6KyqrHF7pC41DyGKH", salutation: "1", speciality: "1", cell_phone_number: "1", office_phone_number: "1">
false
#<User id: 33, first_name: "1", last_name: "1", working_at: "1", password_digest: nil, password_confirmation: nil, created_at: "2014-03-20 00:37:54", updated_at: "2014-03-20 00:38:00", email: "aab@gmail.com", encrypted_password: "$2a$10$nw1UHb0PeFUFh17zKRhbsOA.MirNfXW69wj7aRfMSDEw...", reset_password_token: nil, reset_password_sent_at: nil, remember_created_at: nil, sign_in_count: 1, current_sign_in_at: "2014-03-20 00:37:54", last_sign_in_at: "2014-03-20 00:37:54", current_sign_in_ip: "127.0.0.1", last_sign_in_ip: "127.0.0.1", authentication_token: "HHz6KyqrHF7pC41DyGKH", salutation: "1", speciality: "1", cell_phone_number: "1", office_phone_number: "1">

As expected. I have no idea why anything within that if statement would have any impact on anything since its condition is false.

I've clearly misunderstood something extra basic, and I'd love for someone to clear my vision.

Answer 1

Is current_user a method? I'm going to assume it is.

The first time you ask for current_user , it is a method, and it is returning that result. Then, it gets past the if-statement and the interpreter sees that you have defined a LOCAL VARIABLE to current_user (you haven't assigned anything, but you have now overwritten the method, in the local scope, with a local variable of the same name). That local variable has no value, it is nil , so you get nil

Do you have a current_user= method? You need to use "self.current_user = {stuff}" if you want to use the method, instead of defining a local variable.

Example:

class MyClass
  def current_user
    @current_user
  end
  def initialize(u)
    @current_user = u
  end
  def current_user=(u)
    @current_user = u
  end
  def do_things_bad
    p "current user is #{current_user}"
    if false
      current_user = "something else"
    end
    p "current user after if is #{current_user}"
  end
  def do_things_good
    p "current user is #{current_user}"
    if false
      self.current_user = "something else"
    end
    p "current user after if is #{current_user}"
  end
end
thing = MyClass.new("Nathan")
#<MyClass:0x00000100c5def0 @current_user="Nathan">
thing.do_things_bad
#=> "current user is Nathan"
#=> "current user after if is "
thing.do_things_good
#=> "current user is Nathan"
#=> "current user after if is Nathan"

Answer 2

The problem is even though the code in the if statement isn't being executed, it's still being parsed, and Ruby is creating a local variable current_user which prevents access to the method. The code doesn't have to run for Ruby to define the variable for you.

This is the same reason why we don't see any errors when we run this code:

if false
  bar = "foo"
end
bar #=> nil

whereas running this code does generate errors:

baz #=> NameError: undefined local variable or method `baz' for main:Object