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In the User model, we say that a User object has_many associated Entry objects The only thing you need to set up, other than the relationship itself, is a column in the entries table that enables the relationship to work You need to store the id of the associated user with each Entry object, so you need to add an integer column to entries called user_id You could do this by creating a new migration and using a directive such as add_column :entries, :user_id, :integer or by adding the column manually with SQL (through another client) Once the model relationship has been defined and relationships between data have been made which is as easy as, say, entryuser = Userfind(1) you can then access data across the relationship For example, in a view showing an entry, you might have some view code such as this: <p>Posted by <%= entry.

username %> at <%= entrycreated_at %></p> ActiveRecord also supports many-to-many relationships For example, consider the relationship between fictional Student and Class models Students can be associated with more than one class at a time, and each class can contain many students With ActiveRecord, you can define these relationships using a join table and a has_and_belongs_to_many relationship, or through an intermediary model such as Enrollment, which defines the links between Students and Classes using has_many with a :through parameter..

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class ApplicationController < ActionController::Base protected # Returns the currently logged in user or nil if there isn't one def current_user return unless session[:user_id] @current_user ||= User.find_by_id(session[:user_id]) end # Make current_user available in templates as a helper helper_method :current_user # Filter method to enforce a login requirement # Apply as a before_filter on any controller you want to protect def authenticate logged_in true : access_denied end # Predicate method to test for a logged in user def logged_in current_user.is_a User end # Make logged_in available in templates as a helper helper_method :logged_in def access_denied flash[:notice] = "Please log in to continue" redirect_to login_url and return false end end

Whenever a user changes an important piece of data (especially the password), you may want the user to confirm that entry by typing it again. This is the purpose of the :confirmation option. When you use this helper, you create a new virtual attribute called #{field_name}_confirmation. Add this to the User model for password confirmation, as shown in Listing 5-27.

Note It s worth pointing out that a model called Class wouldn t be allowed in Rails, because there s

The current_user method acts like an accessor for the currently logged-in user. Since it returns a User object, we can call instance methods of User on it, such as current_user.login. The authenticate method is our filter method (the one we ll call from individual controllers). It checks whether there is a currently logged-in user via logged_in (which, in turn, checks that there is actually a User returned by current_user) and calls access_denied, if there isn t. access_denied sets a message in the flash and redirects to the login action on the users controller. We want two of these methods available in templates as well: logged_in and current_user. Having logged_in available will allow us to make dynamic decisions about

already a class called Class built in to Ruby. Beware of reserved words and using names that are already used elsewhere!

C ha P ter 13 W eB a PP LI C a t I O N F r a M e W O r K S : r a I LS , S I N a t r a , a N D r a M a Z e

Listing 5-27. validates :confirmation Method in app/models/user.rb: http://gist.github.com/326153 class User < ActiveRecord::Base validates :email, :uniqueness => true, :length => { :within => 5..50 }, :format => { :with => /^[^@][\w.-]+@[\w.-]+[.][a-z]{2,4}$/i } validates :password, :confirmation => true has_one :profile has_many :articles, :order => 'published_at DESC, title ASC', :dependent => :nullify has_many :replies, :through => :articles, :source => :comments end The password attribute is a column in the users table, but the password_confirmation attribute is virtual. It exists only as an in-memory variable for validating the password. This check is performed only if password_confirmation isn t nil and runs whenever the object is saved.