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 _at_ represents local scope within an object
  instance
• _at__at_ 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
  bashAvatar hays rubyprint "howdy world!"d
• Or, use ruby -e "command"ruby -e 'puts
  "hello\n"'
• Or, you can just use irb, which is
  easierAvatar hays irbgtgt print "howdy
  world!"howdy world!gt nilgtgt

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/2007/01/2
2/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)
_at_name name _at_type type _at_color
color _at_attribute attribute end
13
creating a new cat

• Now, I can create an instance of the cat
  classgc 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 _at_name " is a " _at_color " "
  _at_type " who is " _at_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"_at_name is a
  _at_color _at_type who is _at_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_namedef
  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
• Soa "my value"b a
• a0 "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 assignmentmy_array
  "one", "two", 3, 4
• Referencing the arrayputs "my_array0 is
  my_array0\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 assignmentmy_hash 'tree'
  gt 'pine', 'bird' gt '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
  filedef helloend
• And some html in the app/views/bark folder,
  hello.html.erb

lthtmlgtltheadgtlt/headgt ltbodygt lth3gtHowdylt/h3gt lt/bodygt
lt/htmlgt
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 dbcreateall ruby
script/generate scaffold Person lnamestring
fnamestring emailstringrake dbmigrate ruby
script/server
39
Sources

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