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Action Pack Sessions and Architecture


In this twelfth part of a multi-part series on the Action Pack library for Rails, we'll focus on the architecture of Rails and how the system handles session data. This article is excerpted from chapter six of the book Beginning Rails: From Novice to Professional, written by Jeffery Allan Hardy, Cloves Carneiro Jr. and Hampton Catlin (Apress; ISBN: 1590596862).

Author Info:
By: Apress Publishing
Rating: 5 stars5 stars5 stars5 stars5 stars / 4
June 16, 2011
TABLE OF CONTENTS:
  1. · Action Pack Sessions and Architecture
  2. · Using the Session

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Action Pack Sessions and Architecture - Using the Session
(Page 2 of 2 )

Secure in the knowledge that Rails will take care of all the low-level details of sessions for us, using the session object couldnít be easier. The session is implemented as a hash, just like the flash. We should come clean here. The flash is, in fact, a session in disguise (you can think of it as a specialized session due to its auto-expiring properties). Not surprisingly, then, the flash and session interfaces are identical. We store values in the session according to a key.

session[:account_id] = @account.id session[:account_id] # => 1

session['message'] = "Hello world!" session['message'] # => "Hello world!"

Logging In a User

Now we can return to our new actions, starting with login . Here, youíll see the session object action (no pun intended).

def login

if request.post?

if user = User.authenticate(params[:login], params[:password])

session[:user_id] = user.id

redirect_to events_url

else flash[:notice] = 'Invalid login/password combination' end end end

First, we check to see if the request method is of the POST variety, which would indicate that the login form had been posted. If itís a GET , meaning no form data has been posted, we just want to render the login template, which will happen automatically since weíre not sending any other response. If we have a POST , though, we use the authenticate class method from our User model to attempt a login (see Listing 5-28 in Chapter 5).

Remember that authenticate returns a User object if the authentication succeeds; otherwise it returns false . Therefore, we can perform our conditional and our assignment in one shot using if user = User.authenticate(params[:login], params[:password]) . If the assignment takes place, we want to store a reference to this user so we can keep the user logged inóa perfect job for the session if there ever was one.

session[:user_id] = user.id

Notice that we donít need to store the entire User object in session. We store just a reference to the userís id . Why wouldnít we want to store the entire User object? Well, think about this for a minute: what if the user is stored in session and then that user later changes her login? The old login would remain in the session and would therefore be stale. This can cause further problems if the underlying User model changes. Your entire object could become stale, potentially causing a NoMethodError when accessing attributes that didnít exist on the model at the time it was placed in session. The best bet is to just store the id .

With a reference to the logged-in user safely stored in session, we can redirect to the events controller.


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