Ruby on Rails

1. Ruby on Rails

2. What's Ruby • A programming language • Developed by Yukihiro Matsumoto (aka Matz) in the 1990s

3. What's Rails • Initially developed by David Heinemeier Hansson, out of his work on Basecamp, a project management system • It is a framework of scripts in ruby that provide for rapid development of web applications, esp those with a database back end • Rails can build the skeleton of an application, including the database tables, in just a few commands

4. Ruby

5. Syntax • Ruby is largely and loosely based on perl (hence the name, according to lore) • Completely object oriented

6. Some Important differences • Unlike PHP, scope in variables is defined by the leading sigil • the $ sign denotes global scope, not a variable • an @ represents local scope within an object instance • @@ represents local scope within a class • A capitalized name is a constant

7. Historical Differences • Javascript--born of the competition between two companies • PHP--created by a varied community • Ruby--the vision of a single person • Rails--the vision of another single person • When you compare these, you can see how the starting point influences the process of development

8. Playing on the Command Line • Ruby is an interpreter, just like php or bash:Avatar:~ hays$ rubyprint "howdy world!"^d • Or, use ruby -e "command":ruby -e 'puts "hello\n"' • Or, you can just use irb, which is easier:Avatar:~ hays$ irb>> print "howdy world!"howdy world!=> nil>>

9. Object Oriented • Truly • Not a prototyping language like javascript • Nor a procedural language with OOP bolted on

10. Classes • A class is a kind of master object • Can contain constants and methods • Instances of object can be created from a class, inheriting the traits of the class

11. A simple class class Cat end (but this class doesn't do or mean anything) the class examples are derived from http://www.juixe.com/techknow/index.php/2007/01/22/ruby-class-tutorial/

12. cat class • I want four attributes for a cat; name, color, type, and attribute class Cat # must be capitalized attr_accessor :name, :type, :color, :attribute def initialize(name, type, color, attribute) @name = name @type = type @color = color @attribute = attribute end

13. creating a new cat • Now, I can create an instance of the cat class:gc = Cat.new("GC", "short hair", "black", "gimpy")lc = Cat.new("LC", "short hair", "black", "little")

14. add a method • I'd like to be able to describe my cats easily • So I add a method to the cat class: def describe @name + " is a " + @color + " " + @type + " who is " + @attribute + ".\n" end

15. eliminating con-cat-ination • The concatenation is a bit awkward • Like php, ruby has a structure for calling variables within a string:"#{@name} is a #{@color} #{@type} who is #{@attribute}.\n"

16. calling the method • If I call a cat with the describe method attached, I can get the description of that cat: my_string= gc.describe puts my_string • or: puts gc.describe

17. finding cats by name • A second method, find_by_name:def self.find_by_name(name) found = nil ObjectSpace.each_object(Cat) { |o| found = o if o.name == name } found end

18. Access Control • Methods in a class are public by default • Private methods are known only to the individual object • Protected methods can only be called by members of the class in which is was defined

19. Variables • In ruby, vars are references to objects, not objects themselves • So:a = "my value"b = a a[0] = "n" will change both a and b--but if you reassign a, eg a="new value", a is linked to a new object (this might bite you, but it's not likely)

20. Arrays • Create an array by assignment:my_array = [ "one", "two", 3, 4 ] • Referencing the array:puts "my_array[0] is: #{my_array[0]}\n" • The brackets are methods of the array class…

21. Hashes • What in php is called an associative array is called a hash in ruby • Creating a hash by assignment:my_hash = { 'tree' => 'pine', 'bird' => 'mocking'}puts "\n"puts "my_hash['tree'] is: #{my_hash['tree']}\n"puts "my_hash['bird'] is: #{my_hash['bird']}\n" • Notice that the syntax is different

22. walking a hash or array • use the each method: a = 1 my_hash.each do |key, value| puts "#{a} #{key} is: #{value}" a = a +1 end

23. conditional • much like php and javascript, but simpler syntax: a = 1 my_hash.each do |key, value| if key == "tree" puts "#{a} #{key} is: #{value}" end a = a +1 end

24. In summary • Ruby's syntax is pretty • Ruby is all about structure • Classes are easy to work with, if you're new, start with simple examples

25. Rails

26. Model View Controller (MVC) • Layering again • MVC allows a project team to work on different aspects of the application without stepping on each other's toes quite so often • Note that neither PHP nor Javascript encourage this, but it can be done in PHP (not so much in Javascript) • Rails enforces MVC

27. Model • Contains the data of the application • Transient • Stored (eg Database) • Enforces "business" rules of the application • Attributes • Work flow

28. Views • Provides the user interface • Dynamic content rendered through templates • Three major types • Ruby code in erb (embedded ruby) templates • xml.builder templates • rjs templates (for javascript, and thus ajax)

29. Controllers • Perform the bulk of the heavy lifting • Handles web requests • Maintains session state • Performs caching • Manages helper modules

30. Convention over Configuration • Notion that coding is reduced if we adopt a standard way of doing things • Eg., if we have a class "Pet" in our model that defines the characteristic of domestic animal, in rails, the database table created for us will be named "pets" • Other chunks of code look for each other by their common names

31. Action Pack • Since views and controllers interact so tightly, in rails they are combined in Action Pack • Action pack breaks a web request into view components and controller compoents • So an action usually involves a controller request to create, read, update, or delete (CRUD) some part of the model, followed by a view request to render a page

32. Processing URLs • The basic url used to access a controller is of the form: http://server/controller/action • The controller will be one you generate, and the action will be one you've defined in your controller • So if you have a controller named "filer" and that controller has an action named "upload", the url will be something like http://127.0.0.1/filer/upload

33. The View • The controller will have a folder in app/view named after it, and in that will be the view templates associated with the action methods • These templates are usually html with some inserted ruby code • While code can be executed in these templates, keep that simple--any data controls should be made in the controller's files

34. Creating a basic site • Three commandsrails democd demoruby script/generate controller Bark • This creates the framework

35. Making it say something • A def in the app/controller/bark_controller.rb file:def helloend • And some html in the app/views/bark folder, hello.html.erb: <html><head></head> <body> <h3>Howdy</h3> </body> </html>

36. Directory Structure • app: most of your code lives here • config: information environment and database link • database.yml • development, test and production versions • doc, log, tmp • lib: your code, just a place to stick things that don't have a good home elsewhere

37. Directory Structure • public: images, javascripts, stylesheets go here • script: script that rails uses, most of these are short and reference files in the lib dir for rails • vendor: 3rd party code

38. Generating a database site • Magic rails temp cd temp rake db:create:all ruby script/generate scaffold Person lname:string fname:string email:stringrake db:migrate ruby script/server

39. Sources • http://github.com/rails/rails/tree/master/actionpack • http://en.wikipedia.org/wiki/Ruby_on_Rails • http://www.whytheluckystiff.net/ruby/pickaxe/ • http://www.pragprog.com/titles/rails3/agile-web-development-with-rails-third-edition • http://www.juixe.com/techknow/index.php/2007/01/22/ruby-class-tutorial/