Short Intro

• Open Source Project
• Web Framework for Ruby
• A MVC Framework
• Philosophy
  • DRY (Don't Repeat Yourself)
  • CoC (Convention over Configuration)

MVC of Rails

Rails Controller

Rails View

HTTP Request

Browser

Rails Model

Database

Rails Structure

• ActiveRecord = Model

• ActionView = View

• ActionController = Controller

• ActionDispatch = Routing

Setup

# First, Install ruby
$ brew install ruby
$ ruby -v
ruby 2.3.1p112 (2016-04-26 revision 54768) [x86_64-linux]

# Then, use `rubyGems` to install `rails`
$ gem install rails --no-ri --no-rdoc
$ rails -v
Rails 5.0.0.1

# However, if you want to install an old version?
$ gem install rails -v 4.2.4 --no-ri --no-rdoc

Setup (Cont.)

# Use `rails` cli to scaffold your project
$ mkdir <project-name>
$ rails new <project-name> --skip-test-unit

# However, if you don't want to use newest version of rails,
# you can give version, in `_x.x.x_` format, as parameter in cli
$ rails _4.2.4_ new <project-name> --skip-test-unit

Setup (Cont.)

Setup (Cont.)

Setup (Cont.)

# cd to your project and use this command to install packages in `Gemfile`
$ cd <project-name>
$ bundle install

# Then, use this command to up your rails server
$ rails server # a.k.a rails s

Scaffold Application

# Use generate scaffold to generate Models, Views, and Controllers
$ rails g scaffold person name:string bio:text birthday:date

Enter localhost:3000

Migration

• Able to manage `db` w/ VCS

• Flexible for app

• Cross-database

Scaffold Application (Cont.)

Ref: Active Record Migrations

Scaffold Application (Cont.)

Migration

class CreatePeople < ActiveRecord::Migration
  def change
    create_table :people do |t|
      t.string :name
      t.text :bio
      t.date :birthday

      t.timestamps null: false
    end
  end
end

Scaffold Application (Cont.)

Migration

class AddNicknameToPeople < ActiveRecord::Migration
  def change
    add_column :people, :nickname, :string
  end
end

Scaffold Application (Cont.)

Layout: Partial Template w/ erb

Example: app/views/people/index.html.erb

Scaffold Application (Cont.)

Interact w/ Rails Application via `rails console`

Scaffold Application (Cont.)

config/routes.rb

RESTful Routes

Ref: RESTful routes provided by the Users resource

Scaffold Application (Cont.)

Validation

class Person < ActiveRecord::Base
  validates :name, length: { maximum: 20 }
end

Ref: Active Record Validation

Scaffold Application (Cont.)

respond_to

Basic ActiveRecord

Basic ActiveRecord (Cont.)

• ORM (Object-relational mapping)
• Active Record Pattern from Martin Fowler in "Patterns of Enterprise Application Architecture"
• Schema Name Convention
  • PK (Primary Key) : Default with an integer id, auto-generated via db:migrate
  • FK (Foreign Key) : Corresponding Table singular name + _id, e.g. user_id

Basic ActiveRecord (Cont.)

CRUD: Create

# `create`: create and save data into database
todo = Todo.create( description: 'Study Ruby on Rails', done: false )

# `new`: assign an instance to a variable and need to use `save` to have transaction with database
todo = Todo.new
todo.description = 'Weekly sharing @ Rakuten'
todo.done = false
todo.save

localhost:3000/todos

Basic ActiveRecord (Cont.)

CRUD: Read

# `all`: return all todos in database
todos = Todo.all

# `first`: return first row in database
todo = Todo.first

# `find_by`: return first todo which is done yet
todo = Todo.find_by(done: false)

# `where`: return all todos which are done yet and ordered by `created_at` in desc
todo = Todo.where(done: false).order('created_at DESC')

Basic ActiveRecord (Cont.)

CRUD: Read

Basic ActiveRecord (Cont.)

CRUD: Update

# Get one row, modify it and use `save` method to update database
todo = Todo.find_by(description: 'Study Ror')
todo.description = 'Study RoR'
todo.save

# Get one row, use `update` method to update database directly
todo = Todo.find_by(description: 'Study Ror')
todo.update(description: 'Study RoR')

First way

Second way

Basic ActiveRecord (Cont.)

CRUD: Delete

# Get one row, and use `destroy` method to delete it from database
todo = Todo.find_by(description: 'Study RoR')
todo.destroy

ActiveRecord Association

Q: If there are multiple models, how can we communicate b/w models?

class Customer < ActiveRecord::Base
end
 
class Order < ActiveRecord::Base
end

ActiveRecord Association

Q: If there are multiple models, how can we communicate b/w models?

A: Use Primary Key (id) and

Foreign Key ({table_name}_id) to communicate b/w them

class Customer < ActiveRecord::Base
  has_many :orders
end
 
class Order < ActiveRecord::Base
  belongs_to :customer
end

ActiveRecord Association (Cont.)

One-to-Many

Customer

Order

Order

Order

Customers

Orders

ActiveRecord Association (Cont.)

One-to-Many

class Customer < ActiveRecord::Base
  has_many :orders # Plural
end
 
class Order < ActiveRecord::Base
  belongs_to :customer # Singular
end

ActiveRecord Association (Cont.)

One-to-One

Q: When should we use 1-to-1 association?Why don't we just combine those tables into one table?

ActiveRecord Association (Cont.)

One-to-One

Q: When should we use 1-to-1 association?Why don't we just combine those tables into one table?

A: Each table has different meaning. On the other hand, this kind of design is always used to reduce amount of search. Let's take a look at example at next page

ActiveRecord Association (Cont.)

One-to-One

Customer

Account

Cusomers

Accounts

ActiveRecord Association (Cont.)

One-to-One

class Customer < ActiveRecord::Base
  has_one :account
end
 
class Account < ActiveRecord::Base
  belongs_to :customer
end

ActiveRecord Association (Cont.)

Many-to-Many

$ rails g model customer_groupship customer_id:integer group_id:integer

Customers

CustomerGroupShips

Groups

ActiveRecord Association (Cont.)

Many-to-Many

class Customer < ActiveRecord::Base
    has_many :customer_groupships
    has_many :groups, :through => :customer_groupships
end

class CustomerGroupship < ActiveRecord::Base
    belongs_to :customer
    belongs_to :group
end

class Group < ActiveRecord::Base
    has_many :customer_groupships
    has_many :groups, :through => :customer_groupships
end

ActiveRecord Association (Cont.)

All methods for association

• belongs_to

• has_one

• has_one :through

• has_many

• has_many :through

Ref: ActiveRecord Association