Learn SQL the Hard Way Ex 6 in Ruby

ex6.rb

require "sqlite3"
require "active_model"
require "active_support"
require "active_support/core_ext/string"
require "pry"

DB = SQLite3::Database.new("./ex6.db")

class Pet
  include ActiveModel::Serializers::JSON

  attr_accessor :id, :name, :breed, :age, :dead

  def attributes=(hash)
    hash.each do |key, value|
      send("#{key}=", value)
    end
  end

  def attributes
    instance_values
  end
end

class Person
  include ActiveModel::Serializers::JSON

  def self.find_by(attributes = {})
    person = new
    row = DB.execute(%(
      SELECT * FROM person
      WHERE #{attributes.map { |k, v| "#{k} = '#{v}'"}.join(" AND ")}
      LIMIT 1
    ).squish).last

    person.from_json({
      id: row[0],
      first_name: row[1],
      last_name: row[2],
      age: row[3]
    }.to_json)
  end

  attr_accessor :id, :first_name, :last_name, :age

  def attributes=(hash)
    hash.each do |key, value|
      send("#{key}=", value)
    end
  end

  def attributes
    instance_values
  end

  def pets
    @pets ||= DB.execute(%(
      SELECT pet.id, pet.name, pet.breed, pet.age, pet.dead
      FROM pet, person_pet, person
      WHERE pet.id = person_pet.pet_id
        AND person.id = person_pet.person_id
        AND person.id = #{id}
    ).squish).map do |row|
      pet = Pet.new
      pet.from_json({
        id: row[0],
        name: row[1],
        breed: row[2],
        age: row[3],
        dead: row[4]
      }.to_json)
    end
  end
end

zed = Person.find_by(first_name: 'Zed')
joe = Person.find_by(first_name: 'Joe')

puts zed.as_json
zed.pets.each { |pet| puts pet.as_json }
puts "-" * 45
puts joe.as_json
joe.pets.each { |pet| puts pet.as_json }

ex6.sql

CREATE TABLE person (
	id INTEGER PRIMARY KEY,
	first_name TEXT,
	last_name TEXT,
	age INTEGER
);

CREATE TABLE pet (
	id INTEGER PRIMARY KEY,
	name TEXT,
	breed TEXT,
	age INTEGER,
	dead INTEGER
);

CREATE TABLE person_pet (
	person_id INTEGER,
	pet_id INTEGER
);

INSERT INTO pet (id, name, breed, age, dead)
  VALUES (0, 'Fluffy', 'Unicorn', 1000, 0);

INSERT INTO pet VALUES (1, 'Gigantor', 'Robot', 1, 1);


INSERT INTO person (id, first_name, last_name, age)
  VALUES (1, 'Joe', 'Sak', 40);

INSERT INTO pet (id, name, breed, age, dead)
  VALUES (2, 'Fuji', 'Calico', 6, 0);

INSERT INTO pet (id, name, breed, age, dead)
  VALUES (3, 'Bizen', 'Gray tabby', 9, 0);

INSERT INTO pet (id, name, breed, age, dead)
  VALUES (4, 'Michu', 'Orange tabby', 3, 0);

INSERT INTO person_pet (person_id, pet_id) VALUES (0, 0);
INSERT INTO person_pet VALUES (0, 1);

INSERT INTO person_pet (person_id, pet_id) VALUES (1, 2);
INSERT INTO person_pet (person_id, pet_id) VALUES (1, 3);
INSERT INTO person_pet (person_id, pet_id) VALUES (1, 4);

Gemfile

source "https://rubygems.org"

ruby "3.3.0"

gem "activemodel"
gem "activesupport"
gem "sqlite3"
gem "pry"

shell

sqlite3 ex6.db < ex6.sql
ruby ex6.rb

{"id"=>0, "first_name"=>"Zed", "last_name"=>"Shaw", "age"=>37}
{"id"=>0, "name"=>"Fluffy", "breed"=>"Unicorn", "age"=>1000, "dead"=>0}
{"id"=>1, "name"=>"Gigantor", "breed"=>"Robot", "age"=>1, "dead"=>1}
---------------------------------------------
{"id"=>1, "first_name"=>"Joe", "last_name"=>"Sak", "age"=>40}
{"id"=>2, "name"=>"Fuji", "breed"=>"Calico", "age"=>6, "dead"=>0}
{"id"=>3, "name"=>"Bizen", "breed"=>"Gray tabby", "age"=>9, "dead"=>0}
{"id"=>4, "name"=>"Michu", "breed"=>"Orange tabby", "age"=>3, "dead"=>0}