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At this point, the application sits there doing nothing. This is because it s waiting to serve HTTP requests (such as from your web browser). Go to your web browser of choice and access the application using the URL given by the output (http://0.0.0.0:3000/ in this case, but it might be http://localhost:3000/ or http://127.0.0.1:3000/ on your machine). You should see a page like the one in Figure 13-2.

Finding an associated object (say, an article) by its id doesn t restrict it to articles owned by a particular user You could pass in the article_id and the user_id as conditions, but that s sloppy and error-prone The correct way to do this is to scope all find operations off the user in question For example, assuming you have a User object stored in the variable current_user, current_userarticlesfind(1) ensures that the article with id 1 is returned only if it belongs to the current_user Anyone who has done database work will realize that this incredibly simple syntax is far easier than the SQL queries that need to be created to achieve similar results.

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Notice that we don t need to store the entire User object in session. We store just a reference to the user s id. Why wouldn t 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 didn t 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.

Ch aPt er 13 W eB a P P L IC a tION Fr a MeW O r K S : r a I LS , S I N a t r a , a N D r a M a Z e

The logout action is fairly straightforward. We clear out the :user_id session by setting its value to nil, and then we redirect back to the login action.

Figure 13-2. The default Rails application index.html page The page you re seeing is the index.html file from the public folder. This is because if no action is found within a Rails application that associates with the URL you re loading from your web browser, a Rails application should return a file from the public folder if any file matches or an error message. Because the default page to load on a web server is usually index.html, public/index.html is returned. When you generated the scaffolding for the Entry model, a controller called entries was created, as app/controllers/entries_controller.rb. By default, you access controller methods in a Rails application using a URL in the format of http://[hostname]/[controller]/ [action].

If you play around with these chains, you can check out the log to see the SQL that s generated be happy that you didn t have to write it yourself! This technique doesn t just apply to finding You can use it to automatically assign ownership with build and create constructors by setting the appropriate foreign keys Consider the following example, which creates a new article for the current_user It automatically sets the article s user_id to that of the current user: current_userarticlescreate(:title => 'Private', :body => Body here. ) This is much better than the alternative, which is to go through the Article model directly and set the user_id as an attribute (Articlecreate(:user_id => current_userid) As a rule, whenever you need to restrict find operations to an owner, or if you re assigning ownership, you should use the power of the association proxy..