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Background 349 The Limitations and Benefits of Our Approach 349 Pros and Cons of the Frameworks Covered 350 Merb: The Missing Framework 350 Rails: Ruby s Killer App 351 What Is Rails and Why Use It 351 Installing Rails 353 Building a Basic Rails Application 355 Controllers and Views 368 Models and Relationships 377 Sessions and Filters 379 Other Features 381 Where to Go Next: References, Books, and Example Apps 386 Sinatra: The Framework for Lightweight, Simple Web Applications 387 The Extreme Simplicity of Sinatra 388 General URL Routing and Parameter Matching 388 Views, Templates, and Static Files 390 Request Flow Control 394 Further Resources 396 Ramaze: A Lightweight, MVC-Focused Web Application Framework 397 Generating a Bare Ramaze App 397 Application Structure and Customization 398 Single-File Applications 408 Further Resources 410 Summary 410.

5 goes through all the specifics of model validations. For now, you re using only the most primitive methods of protecting your data. It shouldn t surprise you that Active Record is capable of much more involved validations, such as making sure a numeric value is entered, validating that data is in the correct format using regular expressions, and ensuring unique values, among other checks.

>> => >> => => event = Event.find(:first) #<Event:0x3258d2c> user = User.create(:login => 'simon', :email => 'simon@example.com', :password 'secret') #<User:0x3251b1c>

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ActiveRecord gives you objects that correspond to rows and classes that correspond to tables, and you can work with the data using Ruby syntax, like so: person = Person.find(:first, :conditions => ["name = ", "Chris"]) person.age = 50 person.save This code looks through the people table for a row whose name column matches Chris, and puts an object relating to that row into person. ActiveRecord makes attributes available for all that row s columns, so changing the age column is as easy as assigning to the object s attribute. However, once the object s value has been changed, you issue the save method to save the changes back to the database.

note The pluralization from a Person class to a people table is an automatic part of ActiveRecord s

Because this user is brand new, it won t have any registrations or activities at this point, nor will the event have any attendees. We can confirm this fact by asking:

NOTE Regular expressions (regex for short) are expressions that describe patterns in strings. They re generally used to give a concise description of a set without having to list all elements. Like most programming languages, Ruby has built-in support for regular expressions.

The previous code could replace SQL such as this: SELECT * FROM people WHERE name = "Chris"; UPDATE people SET age = 50 WHERE name = "Chris"; Even SQL gurus familiar with Ruby tend to find Ruby s syntax more natural, particularly in the scope of a Ruby program. There s no need to mix two different languages in one program if both sets of features can be provided in Ruby alone. ActiveRecord will be covered in detail in 13.

>> => >> => >> => user.registrations.any false user.activities.any false event.attendees.any false

note ActiveRecord is not the only library to offer features that relate objects to database tables. Og,

Now that you ve seen the pages in action, let s look at the articles controller again. As you can see in Listing 3-6, the controller is now chock-full of actions. There s one for each of index, show, new, create, edit, update, and destroy the basic CRUD (Create, Read, Update and Delete) actions. Listing 3-6. The app/controllers/articles_controller.rb File class ArticlesController < ApplicationController # GET /articles # GET /articles.xml def index @articles = Article.all respond_to do |format| format.html # index.html.erb format.xml { render :xml => @articles } end end # GET /articles/1 # GET /articles/1.xml def show @article = Article.find(params[:id]) respond_to do |format| format.html # show.html.erb format.xml { render :xml => @article } end end

DataMapper (http://datamapper.org/), and Lafcadio (http://lafcadio.rubyforge.org/) are three alternatives, though they re far less popular than ActiveRecord. DataMapper is notably used in some alternative web frameworks and should also be supported for direct use in Rails 3.0 (not released at the time of writing).

To register this user for an event, we simply create a new registration object like we would any association, and pass in the event we want to register for. We do this using registrations.create.

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