This document provides an introduction to Ruby on Rails and ActiveRecord. It discusses Ruby syntax and concepts, creating and reading ActiveRecord objects from the database, updating and destroying records, validation, associations between models, and controllers. Key topics covered include defining variables and constants, creating records, finding records by attributes, updating attributes, deleting records, validation helpers like acceptance and uniqueness, belongs_to and has_many associations, and the basic CRUD actions supported by controllers.

1. Ruby on Rails

2. Introduction to Ruby
Ruby Syntax and Concepts
Variables
Constants
Blocks
Hashes

8. Creating active record
user = User.create(name: "David", occupation: "Code Artist")
user = User.new
user.name = "David"
user.occupation = "Code Artist"
 user.save

9. Reading an activerecord from database
users = User.all
user = User.first
david = User.find_by(name: 'David')
users = User.where(name: 'David', occupation: 'Code Artist').order('created_at DESC')

10. Updating Activerecords attributes
user = User.find_by(name: 'David')
user.update(name: 'Dave')
Destroying an ActiveRecors
user = User.find_by(name: 'David')
user.destroy

11. Validation
 create
 create!
 save
 save!
 update
 update!

14. Validation Helpers
Acceptance
class Person < ActiveRecord::Base
 validates :terms_of_service, acceptance: true
end
validates_associated
class Library < ActiveRecord::Base
 has_many :books
 validates_associated :books
end

15. Length
class Person < ActiveRecord::Base
 validates :name, length: { minimum: 2 }
 validates :bio, length: { maximum: 500 }
 validates :password, length: { in: 6..20 }
 validates :registration_number, length: { is: 6 }
end
Uniqueness
class Account < ActiveRecord::Base
 validates :email, uniqueness: true
end

17. Order and list of Model Call Backs

21. Assocaiations
class Customer < ActiveRecord::Base
end
 class Order < ActiveRecord::Base
end
@order = Order.create(order_date: Time.now, customer_id: @customer.id)

22. class Customer < ActiveRecord::Base
 has_many :orders, dependent: :destroy
end

class Order < ActiveRecord::Base
 belongs_to :customer
end
@order = @customer.orders.create(order_date: Time.now)

24. belongs_to
class Order < ActiveRecord::Base
 belongs_to :customer
end

26. has_one :through

27. has_many :

29. The has_and_belongs_to_many Association:

30. Controller

32. CRUD, Verbs, and Actions