Ruby on Rails: An Introduction

1
Ruby on Rails An Introduction

• JA-SIG Summer Conference 2007
• Michael Irion
• The University of Tulsa

2
What is Ruby on Rails (RoR)?

• Ruby on Rails is an open-source, full-stack
  framework for developing database-backed web
  applications according to the Model-View-Control
  pattern

3
Overview of Ruby on Rails

• Ruby is the programming language used to
  manipulate the framework
• Rails is the framework that provides the
  necessary infrastructure
• Rails is written in Ruby

4
Ruby Features

• Ruby is an interpreted language (No compile step
  necessary)
• Ruby is an Object Oriented language.
• Everything is an object (No primitives)
• Ruby draws from Perl, Smalltalk, and Lisp

5
Duck Typing in Ruby

• Objects are dynamic, and their types are
  determined at runtime
• The type of a Ruby object is much less important
  than its capabilities
• If a Ruby object walks like a duck and talks like
  a duck, then it can be treated as a duck

6
Rails Philosophy

• Convention over configuration (no XML)
• Dont Repeat Yourself (DRY)
• Rails is opinionated

7
Rails Architecture

• Rails applications are implemented using the
  Model-View-Controller (MVC)
• Model - ActiveRecord
• View - ActionView
• Controller - ActionController

8
Starting the Bookmarks Application

• Generate application
• gt rails bookmarks

9
Directory Layout

• Rails applications have a common directory
  structure
• /app - the MVC core
• /controllers
• /helpers - provides extra functionality for
  views
• /models
• /views/nameofcontroller - templates for
  controller actions

10
Directory Layout

• /components - will be deprecated
• /config - database, route and environment
  configuration
• /db - database schema and migrations
• /lib - functions that dont map to MVC
• /log
• /public - static web resources (html, css,
  javascript etc.)
• /script - rails utilities
• /test - tests and fixtures
• /tmp
• /vendor - 3rd party plugins

11
Rails Environment Modes

• Rails runs in different modes, depending on the
  parameters given to the server on startup. Each
  mode defaults to its own database schema
• Development (verbose logging and error messages)
• Test
• Production

12
Starting Rails

• gt cd /directorypath/bookmarks
• Start the server
• gt ruby script/server start
• Default environment is development
• Default port is 3000
• http//127.0.0.13000

13
Welcome Aboard - Now What?

• Hello world seems appropriate
• gtruby script/generate controller hello
• exists app/controllers/
• exists app/helpers/
• create app/views/hello
• exists test/functional/
• create app/controllers/hello_controller.rb
• create test/functional/hello_controller_test.r
  b
• create app/helpers/hello_helper.rb

14
Mapping URLs to Controllers and Actions

• http//127.0.0.13000/hello/sayit
• http//127.0.0.13000 - address and port of the
  webserver
• hello - name of the controller
• sayit - name of the action (method in
  controller)

15
Editing the Controller

• def sayit
• render text gt "lth2gtHello World!lt/h2gt"
• end

16
Now for an actual Bookmark

• Edit config/database.yml
• development
• adapter mysql
• database bookmarks_development
• username username
• password password
• host localhost

17
Create the Database

• This step depends on the database and dba tool of
  your choice. Create a new schema/dbname for
  bookmarks_development, and assign rights for the
  user you listed in database.yml.

18
Bookmark Model

• Our bookmark model will (initially) need two
  properties
• URL
• Title

19
Scaffolding for Bookmarks

• Rails can generate all the basic CRUD operations
  for simple models via scaffolding.
• Scaffolding is temporary way to get applications
  wired quickly.
• gt ruby script/generate scaffold_resource
  bookmark urlstring titlestring

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Migrations

• Rails uses migrations to version the database.
• Rails tries to minimize SQL at every opportunity
• Migrations are automatically created whenever you
  generate a new model
• Migration files are located in db/migrations
• The version number is stored in a table called
  schema_info

21
Bookmarks Migration

• located in db/migrate/001_create_bookmarks.rb
• class CreateBookmarks lt ActiveRecordMigration
• def self.up
• create_table bookmarks do t
• t.column url, string
• t.column title, string
• end
• end
• def self.down
• drop_table bookmarks
• end
• end

22
Running the Migration

• Rake is the general purpose build tool for rails,
  much like make, or ant. It has many functions,
  one of which is to control migrations.
• gtrake dbmigrate
• Now the table has been created

23
Bookmarks Table ID

• Bookmarks table has the following fields - id,
  url, and title
• Where did the id field come from?
• Convention of configuration - Rails automatically
  creates an id field for each new table and uses
  it as the primary key

24
Bookmarks Controller

• The /app/controllers/bookmarks.rb default
  action
• def index
• _at_bookmarks Bookmark.find(all)
• respond_to do format
• format.html index.rhtml
• format.xml render xml gt
  _at_bookmarks.to_xml
• end
• End

25
Mapping URLs to Controllers and Actions

• http//127.0.0.13000/bookmarks/
• http//127.0.0.13000 - address and port of the
  webserver
• hello - name of the controller
• / - name of the action (blank maps to the index
  action)

26
Bookmarks Model - Dont Repeat Yourself

• No getters/setters. Rails uses information from
  the database.
• class Bookmark lt ActiveRecordBase
• end

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Bookmarks View

• Located in views/bookmarks/index.rhtml
• lt for bookmark in _at_bookmarks gt
• lttrgt
• lttdgtlth bookmark.url gtlt/tdgt
• lttdgtlth bookmark.title gtlt/tdgt
• lttdgtlth bookmark.description gtlt/tdgt
• lttdgtlt link_to 'Show', bookmark_path(bookmark
  ) gtlt/tdgt
• lttdgtlt link_to 'Edit', edit_bookmark_path(boo
  kmark) gtlt/tdgt
• lttdgtlt link_to 'Destroy', bookmark_path(bookm
  ark), confirm gt 'Are you sure?', method gt
  delete gtlt/tdgt
• lt/trgt
• lt end gt

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Convention over Configuration

• Bookmark model automatically looks for a table in
  the database with a plural form of its name.
  (bookmarks)
• The Bookmarks controller automatically renders
  the template located in views according to the
  controller name and the action (views/bookmarks/in
  dex.rhtml)

29
Ajax Helpers

• Rails allows you to program many AJAX calls in
  ruby, instead of writing javascript directly
• Script.aculo.us and Prototype libraries are
  included
• A quick example. Autocomplete for text boxes

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AJAX Autocomplete

• Add to Bookmarks controller
• auto_complete_for bookmarks, url
• Add to views/bookmarks/edit.rhtml
• lt text_field_with_auto_complete bookmark, url
  gt
• In views/layouts/bookmarks.rhtml, add
• lt javascript_include_tag defaults gt

31
Validations

• Rails has a number of validation helpers that can
  be added to the model.
• class Bookmark lt ActiveRecordBase
• validates_presence_of url, title
• end

32
Validations

• validates_presence_of
• validates_length_of
• validates_acceptance_of
• validates_confirmation_of
• validates_uniqueness_of
• validates_format_of
• validates_numericality_of
• validates_inclusion_in
• validates_exclusion_of
• validates_associated relation

33
Associations - Adding Categories to Bookmarks

• The bookmarks are working great, but it would be
  nice if we could group them by category
• Rails uses associations to build relationships
  between tables
• Associations are independent of database foreign
  key constraints

34
Types of Associations

• has_one
• belongs_to
• has_many
• has_and_belongs_to_many
• has_many model1, through gt model2

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Changes to the Database

• A new categories table needs to be created
• A category_id field needs to be added to the
  bookmarks table
• gt ruby script/generate scaffold_resource
  category namestring
• This creates the all the scaffolding and the
  migration db/migrate/002_create_categories.rb
• Note the category table is pluralized as
  categories.
• gtruby script/generate migration
  alter_bookmarks_add_category_id
• This creates db/migrate/003_alter_bookmarks_add_ca
  tegory_id.rb

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Alter Bookmarks Migration

• def self.up
• add_column bookmarks, category_id, integer
• end
• def self.down
• remove_column bookmarks, category_id
• end
• gtrake dbmigrate

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Types of Associations

• has_one
• belongs_to
• has_many
• has_and_belongs_to_many
• has_many model1, through gt model2

38
Database Relationships

• Parent (or Master) models that have collections
  of other models use the has_many relationship
• Child (or Detail) models contain the id field of
  their parent record and they use the belongs_to
  relationship

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Associations Model Code

• class Bookmark lt ActiveRecordBase
• validates_presence_of url, title
• belongs_to category
• end
• class Category lt ActiveRecordBase
• has_many bookmarks
• end

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Associations Controller code

• def edit
• _at_bookmark Bookmark.find(paramsid)
• _at_categories Category.find(all)
• end

41
Associations View Code

• ltpgt
• ltbgtCategorylt/bgtltbr /gt
• lt collection_select('bookmark',
  'category_id', _at_categories, 'id', 'name') gt
• lt/pgt

42
Tools

• Textmate (Mac OS X)
• RadRails (Eclipse plugin) www.radrails.org
• Other commercial and opensource IDEs are being
  made available

43
Resources

• Programming Ruby The Pragmatic Programmers'
  Guide - Second Edition
• Agile Web Development with RailsSecond Edition
• Rails main site http//www.rubyonrails.com
• My email michael-irion_at_utulsa.edu