We sometimes have to read library codes for curiosity or bug fixes. However, there are some techniques needed, so I’ll write them down here.

bundle config set path ‘vendor/bundle’ —- local

Codes of library become visible in our projects and it has become possible to insert pry codes into libraries.

class Book
def read
> Book.new.method(:read).source_location
=> ['book.rb', 2]




・puts caller

class BooksController < ApplicationController
def index
puts caller
# caller is default in Ruby

・backtrace(this is in byebug)

That’s all! Make debugging more effective by using techniques above.

An incident happened that our application in a production environment didn’t read environment variables. OS is Ubuntu and the deploy tool we use is capistrano.

At first, though I wrote environment variables in .bash_profile, they weren’t read. However, when I logged in a production server with ssh and checked them out, they were read.

The reason is below.

“By default Capistrano always assigns a non-login, non-interactive shell.”

Thus, .bash_profile is not read in capistrano by default.

I wrote environment variables in ~etc/environment of Ubuntu in order to iron out the issue and it worked!

Suppose we develop mailer functions and want to test it, what should we do?

The answer is below. The code is following the library above.

RSpec.describe 'test', type: :request do
include ActiveJob::TestHelper

context 'test1' do
def call
# ....some mailer functions
it 'send an email' do
expect { call }.to have_enqueued_job.on_queue('mailers')
expect(enqueued_jobs.size).to eq 1

have_enqueued_job returns…

[{:id=>"xxxxxxxxxxxxxxxx", :job=>ActionMailer::DeliveryJob, :args=>["Mailer", "method", "deliver_now", {"_aj_globalid"=>"gid://product/class/:id"}], :queue=>"mailers"}]

When I faced this problem, I spent 3~4 hours solving it. I’ll summarize it in order not to forget it again.

User.transaction do   
user = User.create!(param)

It is a pity that this code sometimes doesn’t work because UserMailWorker is executed before transaction is committed. Thus, there is no user when Worker is executed. This issue is mentioned in Sidekiq.

It is very simple.

User.transaction do   
user = User.create!(param)

This code will work rightly!

I used sidekiq-cron gem below for the first time. It was so handy I thought I would use it many times in the future. I’ll summarize how to use it in order not to forget it.

This gem is a scheduling application for sidekiq. It is possible to execute scheduled…

This is a famous trick in object oriented programming, so I thought that it needed writing down. The codes are quoted from “practical object-oriented design in ruby”.

class Trip  attr_reader :bicycles, :customers, :vehicle  def prepare(prepares)    prepares.each { |preparer|      case preparer      when Mechanic        preparer.prepare_bicycles(bicycles)      when TripCoordinator        preparer.buy_food(customers)      when Driver        preparer.gas_up(vehicle)

Tomoharu Tsutsumi

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