ORM Lecture

create_table.sql

CREATE TABLE instructors (
  id       SERIAL PRIMARY KEY NOT NULL,
  name     VARCHAR(100),
  coolness INT DEFAULT 5
);

Gemfile

gem 'pg'

instructor.rb

require 'pg'

class Instructor

  # These are my database credentials. You'll need to replace them with yours.
  CONN = PG::Connection.new({
                                host: 'localhost',
                                user: 'postgres',
                                password: 'postgres',
                                dbname: 'ormlecture'
                            })

  attr_accessor :name, :coolness
  attr_reader :id

  def initialize(name, coolness, id=nil)
    @name = name
    @coolness = coolness
    @id = id
  end

  def is_new?
    @id.nil?
  end

  def valid?
    @coolness > 9000
  end

  def save
    raise 'Invalid Instructor!' unless valid?
    if is_new?
      result = CONN.exec_params('INSERT INTO instructors (name, coolness) VALUES ($1, $2) returning id', [@name, @coolness])
      @id = result[0]['id']
    else
      CONN.exec_params('UPDATE instructors SET name = $1, coolness = $2 WHERE id = $3', [@name, @coolness, @id])
    end
  end

  def destroy
    CONN.exec_params('DELETE FROM instructors WHERE id = $1', [@id])
  end

  ## DANGER Below is wet wet code. It's up to you to DRY it out and make it more succinct.
  
  def self.find(id)
    result = nil
    CONN.exec_params('SELECT id, name, coolness FROM instructors WHERE id = $1 LIMIT 1', [id]) do |rows|
      rows.each do |row|
        result = Instructor.new(
            row['name'],
            row['coolness'],
            row['id']
        )
      end
    end
    result
  end

  def self.all
    results = []
    CONN.exec_params('SELECT id, name, coolness FROM instructors') do |rows|
      rows.each do |row|
        results << Instructor.new(
            row['name'],
            row['coolness'],
            row['id']
        )
      end
    end
    results
  end

  def self.where_coolness_above(coolness)
    results = []
    CONN.exec_params('SELECT id, name, coolness FROM instructors WHERE coolness > $1', [coolness]) do |rows|
      rows.each do |row|
        results << Instructor.new(
            row['name'],
            row['coolness'],
            row['id']
        )
      end
    end
    results
  end

end

main.rb

require './instructor'

# david = Instructor.new('David', 1)
# david.save
#
# don = Instructor.new('Don', 50)
# don.save
#
# khurram = Instructor.new('Khurram', 5432)
# khurram.save
#
# arvinder = Instructor.new('Arvinder', 6)
# arvinder.save


# puts Instructor.find(1).inspect
# puts Instructor.find(2).inspect
# puts Instructor.find(3).inspect
# puts Instructor.find(4).inspect
# puts Instructor.find(5).inspect

# Instructor.all.each do |instructor|
#   puts "#{instructor.name} is a #{instructor.coolness}"
# end

# instructor1 = Instructor.find(1)
# instructor1.coolness = 62
# instructor1.save

# puts Instructor.find(1).inspect

# monica = Instructor.new('Monica', 1000)
# monica.save
# puts monica.inspect

# instructor3 = Instructor.find(3)
# instructor3.destroy

Instructor.all.each do |instructor|
  instructor.coolness = 9001
  instructor.save
end

instructor2 = Instructor.find(2)
instructor2.coolness = 8999
instructor2.save

Instructor.where_coolness_above(9000).each do |instructor|
  puts "#{instructor.name}'s coolness is OVER 9000!!!!!"
end