cheeyeo

ActiveRecord::Base.transaction do
  @order.destroy!
  @user.save!
end

# calling the bang methods will raise an exception and cause the transaction not to occur if errors exist. calling save and non-bang will not raise
# any errors at all

* Each transaction opens up a new database connection

cheeyeo

Transactions

As your business logic gets complex you may need to implement transactions. The classic example is a bank funds transfer from account A to account B. If the withdrawal from account A fails then the deposit to account B should either never take place or be rolled back.

Basics

All the complexity is handled by ActiveRecord::Transactions. Any model class or instance has a method named .transaction. When called and passed a block, that block will be executed inside a database transaction. If there's an exception raised, the transaction will automatically be rolled back.

Example

cheeyeo

begin
  update_purchase_captured_at!(purchase, captured_at)
rescue Exception => e
  Honeybadger.notify(e)

  Rails.logger.error(%Q{\
[#{Time.zone.now}][rake purchases:update_captured_at] Error updating \
captured_at for purchase #{purchase.id}: #{e.class}: #{e.message}

This means the funds got captured, but the order will *not* be fulfilled!

cheeyeo

daemon off;
# Heroku dynos have at least 4 cores.
worker_processes <%= ENV['NGINX_WORKERS'] || 4 %>;

events {
  use epoll;
  accept_mutex on;
  worker_connections 1024;
}

cheeyeo

class User
  attr_accessor :name, :pet_name
end

class Post
end

class Factory < BasicObject
  def initialize
    @attributes = {}

cheeyeo

# app/models/importer.rb
class Importer
  include ActiveModel::Validations
  include ActiveModel::Conversion

  VALID_IMPORT_TYPES = ['contact']

  validates :import_type, inclusion: { in: VALID_IMPORT_TYPES }

  attr_reader :parser, :import_type

cheeyeo

# A small DSL for helping parsing documents using Nokogiri::XML::Reader. The
# XML Reader is a good way to move a cursor through a (large) XML document fast,
# but is not as cumbersome as writing a full SAX document handler. Read about
# it here: http://nokogiri.org/Nokogiri/XML/Reader.html
# 
# Just pass the reader in this parser and specificy the nodes that you are interested
# in in a block. You can just parse every node or only look inside certain nodes.
# 
# A small example:
# 

cheeyeo

# I'm no benchmark guru. Just did a bunch of:
$ time ruby <filename>

# Note: This is just an 80mb XML file with 38,000 nodes.

ox_dom.rb        4.56s  user 0.78s system 93% cpu 5.714  total (550mb)
ox_dom.rb        4.58s  user 0.79s system 87% cpu 6.126  total (550mb)
ox_dom.rb        4.60s  user 0.80s system 87% cpu 6.140  total (550mb)
nokigiri_dom.rb  11.75s user 1.02s system 94% cpu 13.518 total (895mb)
nokigiri_dom.rb  11.36s user 1.02s system 93% cpu 13.211 total (895mb)

cheeyeo

module Kernel
  def system(*args)

    rd, wr = IO.pipe

    # Create a new subprocess that will just exec the requested program.
    pid = fork do
      # The sub-process closes its copy of the reading end of the pipe
      # because it only needs to write.
      rd.close

cheeyeo

#!/usr/bin/ruby -w

require 'csv'
require 'active_support/core_ext'

class Parser

  attr_accessor :input_folder
  attr_accessor :output_folder
  attr_accessor :filename