The Ruby in Rails

Presented at the CorkDev user group.

Everyone has probably heard about Rails on Rails the web framework, but what is it about Ruby-the-language that enabled it? Why couldn’t Rails have come out of the Java world? Which features of Ruby produced such easy to read code? Which features enabled that famed ‘convention-over-configuration’ approach?

In this code-focused talk, I’ll show you the machinery behind lines from an example Rails app, explain how the language features work, and why they make Rails such a productive framework. I’ll cover symbols, blocks, iterators, meta-programming, and much more. But I’ll keep it simple as I’m also a bear of very little brain.

Transcript

1. The Ruby in Rails A peek behind the curtain of Rails
2. Disclaimer I've intentionally simplified things to make parts of this presentation easier
3. Ruby • a dynamic scripting language • elegant, natural, friendly • principle of least surprise • 21 years old (that's older than Java)
4. Ruby is designed to make programmers happy. — Yukihiro Matsumoto (Matz)
5. 3.times do print "Ruby is easy!" end • No brackets (mostly optional) • No semicolons • Everything is an object • …that you call methods on
6. Rails • is a web framework • built in Ruby • 10 years old! (no longer the new hotness) • convention over configuration • don't repeat yourself
7. Rails is the killer app for Ruby. — Yukihiro Matsumoto (Matz)
8. Rails is an MVC framework and it looks like…
9. Models Represent rows in the database class User < ActiveRecord::Base has_many :projects validate_presence_of :username, :email end user = new User username: "jamie" user.email ='jamie@ideasasylum.com' user.save User.find_by_username 'jamie'
10. Views HTML templates (or json, or xml, or whatever) <!-- show.html.erb --> <div> <ul> <% @user.projects.each do |project| %> <li><%= link_to project %></li> <% end %> </ul> </div>
11. Controllers The meat of the application class UsersController < ApplicationController # /users/:username def show @user = Users.find_by_username params[:username] end end
12. Let's talk about that code
13. :symbols In our User class… validate_presence_of :username, :email Symbols are constant strings, a bit like public static final String in Java We could also have written: validate_presence_of 'username', 'email'
14. :symbols everywhere • they look a little cleaner • they prevent memory allocation • no confusion about equality testing has_many :projects validates_presence_of :name, :if => :signed_in? before_filter :logged_in?, only: [:edit, :update] User.where :username => 'jamie', :email => 'jamie@ideasasylum.com'
15. Hashes (Dictionaries, Hashmaps, whatever you call 'em') attrs = { :name => 'Jamie', :email => 'jamie@ideasasylum.com' } attrs[:name] #=> 'Jamie' attrs[:name] = 'James' Alternate Hash syntax attrs = { username: 'jamie', email: 'jamie@ideasasylum.com' }
16. Hashes as the last argument User.where username: 'jamie', email: 'jamie@ideasasylum.com' This is passing a hash with the name and email keys to the where(opts) method Equivalent to: attrs = { :name => 'Jamie', :email => 'jamie@ideasasylum.com' } User.where attrs
17. Missing Methods # from UsersController User.find_by_username 'jamie' Where was this method declared? It wasn't Whenever you call a method that doesn't exist, Ruby calls obj.method_missing with the method name and args …and you can override this :-)
18. Missing Methods Found class User def method_missing name, args* column_name = name.match(/find_by_(\w+)/)[1] sql = "SELECT * FROM users WHERE #{column_name} = '#{args[0]}'" # query the database… end end User.find_by_username 'jamie' # SELECT * FROM users where username = 'jamie'
19. Blocks 4.times do print 'Ruby ' end print 'Aha-aha-aaa' Blocks (do…end) are pieces of code that we can pass around to other methods @user.projects.each do |project| link_to project end
20. Implementing .times class CorkDevNumber def initialize num @value = num end def times &block for i in 1..@value yield end end end CorkDevNumber.new(4).times do print 'Ruby ' end
21. Meta-Programming Where did the user.projects method comes from? We didn't declare it! class User < ActiveRecord::Base has_many :projects end
22. has_many methods has_many is a class-level method on ActiveRecord::Base. It creates new methods according the arguments we pass in when the class is loaded. projects projects=object projects_singular_ids projects<<(object, ...) projects.where(...) projects.create(attributes = {})
23. Implementing has_many class Jamie def self.has_many things # getter define_method "#{things.to_s}" do @things end # setter define_method "#{things.to_s}=" do |value| @things = value end end end
24. Ruby is simple in appearance, but is very complex inside, just like our human body. — Yukihiro Matsumoto (Matz)
25. …the same can be said of Rails — Jamie Lawrence (@ideasasylum)