sqlite-ar-test.rb

require 'active_record'

db_adapter = RUBY_PLATFORM == 'java' ? 'jdbcsqlite3' : 'sqlite3'
#db_name = ':memory:'
db_name = 'sqlite-ar-test.sqlite3'

ActiveRecord::Base.establish_connection adapter: db_adapter, database: db_name

ActiveRecord::Schema.define do
  create_table :books, force: true do |t|
    t.string :title
    t.references :author
  end 

  create_table :authors, force: true do |t|
    t.string :name
  end
end

class Book < ActiveRecord::Base
  # A book has only one author.
  belongs_to :author

  def author_name
    unless author.nil?
      author.name
    else
      ''
    end
  end

  def to_s
    "Title:  #{title}\nAuthor: #{author_name}"
  end
end

class Author < ActiveRecord::Base
  # An author can have many books.
  has_many :books

  def to_s
    name
  end
end

Author.new(name: 'Author 1').save
Author.new(name: 'Author 2').save
Author.new(name: 'Author 3').save

puts "Authors: #{Author.all.inspect}"
Author.all.each do |author|
  puts author.to_s
end

Book.new(title: 'Book 1').save

puts "Books: #{Book.all.inspect}"
Book.all.each do |book|
  puts book.to_s
end

author2 = Author.find_by_name 'Author 2'
author2.name = 'Ernest Hemingway'
author2.save
p author2

book1 = Book.find_by_title 'Book 1'
book1.author = author2
book1.title = 'A Farewell to arms'
book1.save
p book1

book2 = Book.new(title: 'The Sun also rises')
book2.author = author2
book2.save

author3 = Author.find_by_name 'Author 3'
author3.name = 'Joseph Heller'
author3.save

book3 = Book.new(title: 'Catch-22')
book3.author = author3
book3.save

puts "Books: #{Book.all.inspect}"
Book.all.each do |book|
  puts book
  puts
end

# TODO
puts 'Hemingway books - a hackish way:'
#Book.find_by_author('Ernest Hemingway').each do |book|
Book.where(author_id: Author.find_by_name('Ernest Hemingway')).each do |book|
  puts book
  puts
end

# TODO
puts 'Hemingway books - a more elegant way:'
Author.where(name: 'Ernest Hemingway').first.books.each do |book|
  puts book
  puts
end

puts 'All books - raw SQL:'
#p Book.connection.select_all 'SELECT * FROM books;'
p ActiveRecord::Base.connection.select_all 'SELECT * FROM books;'