Ruby on Rails Tutorial by Michael Hartl, Chapter 8, "Current User" section - railstutorial.org

Question

I'm new to Rails and have been going through the Rails Tutorial by Michael Hartl. Up until this point, I've been able to understand everything in the tutorial but now I think I'm stuck midway through Chapter 8. I'd like some confirmation from more experienced Rails programmers, that I'm following the author's explanation correctly. I'm talking specifically about Chapter 8, Section 8.2.3 below:
In Section 8.2.3, the "sign_in" method has the line:
self.current_user = user
So by using "self" instead of just "current_user", current_user has been made part of the Session, but not yet stored in the database, correct?
If that's the case, the methods listed in Listing 8.22 are getter and setter methods, correct? The first to store current_user in the DB, and the second to retrieve it as needed?
And finally, the getter and setter methods are needed because its bad practice to expose an instance variable in a method (in this case "sign_in")? In other words, it would be bad to replace:
self.current_user = user
with
#current_user = user
in the "sign_in" method?
I appreciate any help and advice.
Thank you.

Answer 1

I am not highly proficient in Rails, but here is my layman's understanding of the methods in SessionsHelper.
Firstly, #current_user is an instance variable of module SessionsHelper. This means that it persists for subsequent calls of the methods in SessionsHelper.
def sign_in(user)
cookies.permanent[:remember_token] = user.remember_token
self.current_user = user
end
So by using "self" instead of just "current_user", current_user has been made part of the Session, but not yet stored in the database, correct?
self.current_user = user does not make 'current_user' a part of anything.
self refers to itself, SessionsHelper.
self.current_user = effectively calls its own method, the setter method, def current_user=(user).
If that's the case, the methods listed in Listing 8.22 are getter and
setter methods, correct?
Yes.
def current_user=(user) # Setter.
#current_user = user
end
The first to store current_user in the DB,
No. The first method, current_user=, does not store anything into the database. All it does is set the instance variable #current_user to user.
def current_user # Getter.
#current_user ||= User.find_by_remember_token(cookies[:remember_token])
end
and the second to retrieve it as needed?
The second method, current_user, returns an existing #current_user value.
If #current_user is nil(null), it runs
||= User.find_by_remember_token(cookies[:remember_token])
which retrieves and sets #current_user as the User from the database based on the browser's remember_token cookie.
And finally, the getter and setter methods are needed because its bad practice to expose an instance variable in a method (in this case "sign_in")?
In my opinion, the getter and setter methods are not exactly needed. It is possible to just use #current_user throughout the helper.
However, Devise (a popular user authentication gem) utilises the current_user method in its helpers. This comment is relevant as well.
In other words, it would be bad to replace: self.current_user = user with #current_user = user in the "sign_in" method?
There should be nothing wrong with replacing it with #current_user = user. This question (same link as linked comment above) shows you that the functionality is identical in the case of the tutorial.