jenny-codes

# Let f(N) be the number of 8s that occur when you write out all the numbers from 1 to N.
# For example:
# f(6) = 0
# f(8) = 1
# f(20) = 2
# f(80) = 9
# f(100) = 20

def f(N)
  base = []

jenny-codes

# Error module to Handle errors globally
# include Error::ErrorHandler in application_controller.rb
module Error
  module ErrorHandler
    def self.included(clazz)
      clazz.class_eval do
        rescue_from StandardError, with: :standard_error
      end
    end

jenny-codes

# source: http://blog.nicksieger.com/articles/2006/09/06/rubys-exception-hierarchy/

exceptions = []
tree = {}
ObjectSpace.each_object(Class) do |cls|
  next unless cls.ancestors.include? Exception
  next if exceptions.include? cls
  next if cls.superclass == SystemCallError # avoid dumping Errno's
  exceptions << cls
  cls.ancestors.delete_if {|e| [Object, Kernel].include? e }.reverse.inject(tree) {|memo,cls| memo[cls] ||= {}}

jenny-codes

# source: https://openhome.cc/Gossip/Ruby/Proc.html
#         https://openhome.cc/Gossip/Ruby/IteratorBlock.html
#         https://tonytonyjan.net/2011/08/12/ruby-block-proc-lambda/

# self-built reduce function
class Array
  def my_reduce(value = 0)
    for i in 0...self.length
      value = yield(value, self[i])
    end

jenny-codes

# app/controllers/application_controller.rb
class ApplicationController < ActionController::Base
  before_action :ensure_domain
  
  private
  def ensure_domain
    if request.env['HTTP_HOST'] == "jennycodes.herokuapp.com"
      redirect_to "https://jennycodes.me#{request.env['REQUEST_PATH']}", status: 301
    end
  end

jenny-codes

# ActiveRecord::Base.logger = Logger.new(STDOUT)

Speaker.count # 1873
Talk.count    # 1576

Speaker.includes(:talks).to_a
# SELECT `speakers`.* FROM `speakers`
# SELECT `talks`.* FROM `talks` WHERE `talks`.`speaker_id` IN (1, 2, 3,...(omitted)

Speaker.preload(:talks).to_a

jenny-codes

# Speaker -> Talks

# CORRECT USAGE
# Select speakers that have one or more talks and returns all attributes (columns) plus talk's title.
Speaker.joins(:talks).select('distinct speakers.*, talks.title as talks_title').to_a
# SELECT distinct speakers.*, talks.title as talks_title FROM `speakers` INNER JOIN `talks` ON `talks`.`speaker_id` = `speakers`.`id`

# Select speaker whose associated talk(s) is at status 5.
Speaker.joins(:talks).where(talks: {status: 5})
# SELECT `speakers`.* FROM `speakers` INNER JOIN `talks` ON `talks`.`speaker_id` = `speakers`.`id` WHERE `talks`.`status` = 5

jenny-codes

require 'benchmark/ips'

def test
  Benchmark.ips do |bm|
    bm.report('#preload   ') do
      Speaker.preload(:talks).to_a
    end

    bm.report('#eager_load') do
      Speaker.eager_load(:talks).to_a

jenny-codes

require 'thwait'
require 'pg'

start = Time.now

first_sleep = Thread.new do
  puts 'Starting sleep 1'
  conn = PG::Connection.open(dbname: 'test')
  conn.exec('SELECT pg_sleep(1);')
  puts 'Finished sleep 1'

jenny-codes

def send_money(amount)
  puts "Sending $#{amount}"
  sleep 1  # Simulate network call sending of money
end

lock = Mutex.new
threads = []
money_is_sent = false

2.times do