nguyenngochai hoasung01

System Design Cheatsheet

Picking the right architecture = Picking the right battles + Managing trade-offs

Basic Steps

Clarify and agree on the scope of the system

User cases (description of sequences of events that, taken together, lead to a system doing something useful)
- Who is going to use it?
- How are they going to use it?

#SOLID Principles with ruby examples

##SRP - Single responsibility principle A class should have only a single responsibility.

Every class should have a single responsibility, and that responsibility should be entirely encapsulated. All its services should be narrowly aligned with that responsibility, this embrace the high cohesion.

##OCP - Open/closed principle Software entities should be open for extension, but closed for modification.

Adding an audit log to your Rails app

If you have any sort of administrative interface on your web site, you can easily imagine an intruder gaining access and mucking about. How do you know the extent of the damage? Adding an audit log to your app is one quick solution. An audit log should record a few things:

controller entry points with parameter values
permanent information about the user, like user_id
transient information about the user, like IP and user_agent

Using the Rails framework, this is as simple as adding a before_action to your admin controllers. Here’s a basic version that I’m using in production.

Most active GitHub users (git.io/top)

The count of contributions (summary of Pull Requests, opened issues and commits) to public repos at GitHub.com from Sat, 04 Oct 2014 19:10:54 GMT till Sun, 04 Oct 2015 19:10:54 GMT.

Only first 1000 GitHub users according to the count of followers are taken. This is because of limitations of GitHub search. Sorting algo in pseudocode:

githubUsers
 .filter((user) -&gt; user.followers &gt; 474)

Introduction

Vocabulary

Examples are decalred using the it method
Assertions are called Expectations
should and should_not are called Modifiers
Matchers are the operators in the assertions (==, >, be_true, etc.)

Install RSpec

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.

	## Canonical redirect for Apache

	# BEGIN Canonical Redirect
	<IfModule mod_rewrite.c>
	RewriteEngine On
	RewriteCond %{HTTP_HOST} !^www\.domain\.com$ [NC] ## will match any domain that's not our main domain
	RewriteRule ^(.*)$ http://www.domain.com/$1 [R=301,L]
	</IfModule>
	# END Canonical Redirect

	// information made available through the dataLayer is easily used in Google Tag Manager.
	// GTM-XXXXXX has to be changed to the actual GTM-code as shown in the implementation document
	dataLayer = [{
	'pageTitle': 'page title variable', //example
	'loggedIn': 'TRUE', //example
	'CLV': '2249.50', //example (only use . seperator for cents)
	'userID': 'AB12345678' //example
	}];

	<!-- Google Tag Manager -->

	config.assets.precompile += [

	# precompile any CSS or JS file that doesn't start with _
	/(^inline[^_\/]\|\/[^_])[^\/]*.(js\|css)$/,
	...

	# This is a skeleton for testing models including examples of validations, callbacks,
	# scopes, instance & class methods, associations, and more.
	# Pick and choose what you want, as all models don't NEED to be tested at this depth.
	#
	# I'm always eager to hear new tips & suggestions as I'm still new to testing,
	# so if you have any, please share!
	#
	# @kyletcarlson
	#
	# This skeleton also assumes you're using the following gems:

nguyenngochai hoasung01