Ruby on RailsJune 17, 2011

Elpizo Choi

What is Ruby on Rails?

• MVC Framework for building web apps in Ruby• Uses Ruby classes to abstract out the various

components of an app• Convention over configuration

Main Components

• ActiveRecord (ORM – think hibernate)

• ActionController (business logic, routing)

• ActionView (template parser)

• Migrations, rake tasks

Creating a Rails app

Basic folder structure

apps foldercontrollers, models, views – where you’ll spend most your time

database.ymlConfigures database

GemfileConfigures external libraries used in app

… a little configuration

…a little configuration

Let’s make a model

ActiveRecord::Base

• When inherited, maps to table that’s plural of class name– Team -> teams

• Basic methods– Team.create()– Team.find()– Team.where().limit().sort().skip().first– Team.where().limit().sort().skip().all

…first we need to create table

…first we need to create table

…first we need to create table

Rake

• Ruby build tool• rake –T to see all available tasks• rake db:migrate will run all database migrations that haven’t been run• Stores migrations that have already been run

Create a new Team

Querying

More in-depth tutorial:

http://guides.rubyonrails.org/active_record_querying.html

The “web” part of web-app

Let’s get this running

What happened?

What happened?

What happened?

• config/routes.rb defines how urls are mapped to controllers– get “teams/index” is shorthand for:– match “teams/index” => “teams#index”, :via => :get

• More details: http://guides.rubyonrails.org/routing.html

• Read comments in config/routes.rb

Let’s make some changes

Let’s make some changes

Let’s make some changes

Controller

• Logic to be run every time the mapped route is hit

• All code in the corresponding method will happen as side effects

• Instanced variables set here are available to the template

View

• .erb is E-Ruby

• Add as extension to allow the default Rails template engine to parse Ruby code inside HTML

View• Basic HTML

• <% %> tag: Ruby code to be run, but not shown

• <%= %> tag: Ruby code to be run and shown

• ^^ important: because everything in Ruby returns something (in this case it’ll be @team object from the block)

Creating relationships

Creating relationships

Create the player

Add foreign key

Creating relationships

Creating relationships

Gotta reload console after changing models

Get players

But wait! There’s a shortcut!

has_many basically does the following:• looks in a table with same name as its argument (players) • for records whose foreign key column corresponds to the

current class (team_id)• and where the value is the current instance id (1)

Likewise…You can either do this…. …or this:

It’ll accomplish the same thing:

We can now change our view

We can now change our view

More associations

• ActiveRecord also has shortcuts for:– has_and_belongs_to (join tables)– Polymorphic associations (belongs_to different

objects)

• http://guides.rubyonrails.org/association_basics.html

Congratulations!You’ve made your first Rails app

Additional ResourcesSource code for example_app:https://github.com/fuJiin/example_app

See it live:http://cg-example-app.heroku.com/teams/ index

Documentation and light tutorials:http://guides.rubyonrails.org/

More in depth:http://ruby.railstutorial.org/ruby-on-rails-tutorial- book

Questions?