Web Science Stream

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Dr Alexiei Dingli

Web Science StreamModels, Views and

Controllers

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Case Study: digg

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rails shovell

Creating our shovell application

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• To generate a new data model for our application we’ll use the comand below

• Our Story model will get two attributes– Name– Link

• String is a type which holds up to 255 alphanumeric characters

• cd shovell• ruby script/generate model Story name:string link:string

Generating our model

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• exists app/models/• exists test/unit/• exists test/fixtures/• create app/models/story.rb• create test/unit/story_test.rb• create test/fixtures/stories.yml• create db/migrate• create db/migrate/20091019052909_create_stories.rb

The output should be ...

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• story.rb– In the app/model– Creates a blank ActiveRecord

• story_test.rb– Automatically generated unit testing

• stories.yml– Helps our unit testing and is called a Fixture– Fixtures are files containing simple data for unit testing purposes

• 20091019052909_create_stories.rb– A migration file

Let’s look at the output

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• Lightweight format to represent data

• Has the .yml extension

• Have a look at the test/fixtures/stories.yml

YAML

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• # Read about fixtures at http://ar.rubyonrails.org/classes/Fixtures.html

• one:• name: MyString• link: MyString

• two:• name: MyString• link: MyString

stories.yml

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• # Read about fixtures at http://ar.rubyonrails.org/classes/Fixtures.html

• one:• name: My web site• link: http://abc.net

• two:• name: Other web site• link: http://www.theotherwebsite.com

stories.yml

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• Migration files – Used to make modifications to the database

schema– All through Ruby code– No SQL needed– Files are numbered so they can be executed

sequentially– They are executed in order– Located in the db/migrate dir

I’m going to Migrate!

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• class CreateStories < ActiveRecord::Migration• def self.up• create_table :stories do |t|• t.string :name• t.string :link

• t.timestamps• end• end

• def self.down• drop_table :stories• end• end

20091019052909_create_stories.rb

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• Change– create_table :stories do |t|

• To– create_table :stories, :force =>true do |t|

• Useful if we already have some table structures defined in the database

Let’s do a small modification

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• rake is based upon the C make tool• Very versatile and allows us to do a

number of things ...• Try

– rake –T

• In our example we’ll make the migration by invoking– rake db:migrate

Let’s make our migrate

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1. Checks the database for the most recent migration

2. Steps through the migrations that have not been applied

3. For each migration execute the up method

rake db:migrate

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== CreateStories: migrating ==================

-- create_table(:stories)

-> 0.0040s

== CreateStories: migrated (0.0050s) =========

• If it is successful we will find a stories table in our shovell database

The output

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• rake db:migrate version=n

• Eg: undo all the tables in the database by invoking:

– rake db:migrate version=0

Rolling back

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• Open a rails console

– ruby script/console

Playing with the data

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• s = Story.new• s.name = “My new website”• s.link = “http://abc.net”• s.save

• The end result should be• => true

Creating our first record

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• To see the record id– s.id

• To check if its a new record– s.new_record?

• To check the number of Stories in the DB– Story.count

• Another way of creating records– Story.create(

:name => ‘Abc’,

:link => ‘http://www.mysite2.com’)

More on records ...

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• Story.find(2)

• Story.find(:all)

• Story.find(:all).last

• Story.find(:first, :order => ‘id DESC’)

Retrieving records

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• Story.find_by_name(‘Abc’)

• How would we find the link ‘http://abc.net’?

• Try it ...

Dynamic finders ...

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• s = Story.find_by_name(‘Abc’)• s.name = ‘Abcd’• s.save

Let’s update

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• s = Story.find_by_name(‘Abcd’)• s.update_attribute :name. ‘Abcde’

Let’s update and save in just one step

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• s.destroy

• Try to find the record ... what’s the message?

Bye Bye records

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• Have a look at – log/development.log

– CREATE TABLE "stories" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "name" varchar(255), "link" varchar(255), "created_at" datetime, "updated_at" datetime

What about SQL?

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• ruby script/generate controller Stories index

Generating our first controller!

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• exists app/controllers/• exists app/helpers/• create app/views/stories• exists test/functional/• create test/unit/helpers/• create app/controllers/stories_controller.rb• create test/functional/stories_controller_test.rb• create app/helpers/stories_helper.rb• create test/unit/helpers/stories_helper_test.rb• create app/views/stories/index.html.erb

The output

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• First it generates a number of folders (unless they have been created already)

• StoriesController– Has defined the index method

• stories_controller_test.rb– Will hold the test functions

• stories_helper.rb– Class to help the controller

• Index.html.erb– One of the views which will be our initial template

Explaining the output

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• Start a server– ruby script/server

• Goto– http://127.0.0.1:3000/stories

Let’s see what we have so far ...

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Two ways ... With or Without scaffolding!

Creating views

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• A powerful feature of rails• Quickly creates a web interface for

interacting with your model• Provides an easy way to add, manipulate

and delete records• Scaffold generates a model, controller,

actions and other templates

What is scaffolding?

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• Designed for quick interaction only• Not intended as a fully automateed web

site generator• It can’t cope with associations

(relationships) between objects

Limitations of Scaffold

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• ruby script/generate scaffold Story name:String link:String

Let’s scaffold!

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• Scaffold is essentially a script that we invoke using script/generate

• The nice thing about script/generate is that there exists a script/destroy using exactly the same arguments

• So let’s destroy the scaffold– ruby script/destroy scaffold Story name:String

link:String

Script/generate

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• ruby script/generate model Story name:string link:string

• ruby script/generate controller Stories index

Ohh No!! We lost everything!!

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• app/views/stories– Only index.html.erb so far– Generated as a static page– Let’s add some dynamic information

• Insert– <%= Time.now %>

Views

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• We shouldn’t be including ruby code directly in the view

• Ideally we keep them separated so ...– In the /app/controllers/stories_controller.rb

• In the def index add– @current_time = Time.now

– In the app/views/stories/index.html.erb replace the previous code with

– <%= @current_time %>

– Try it out!

Problems!

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• In the controller /app/controllers/stories_controller.rb– In the def index, remove what we just wrote

and write• @story = Story.find(:first, :order => ‘RANDOM()’)

– In the app/views/stories/index.html.erb replace the previous code with

– A random link: <%= link_to @story.name, @story.link %>

Let’s do something more useful

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• Why not add some data and try again?

• ruby script/console• Loading development environment (Rails 2.3.2)• >> s = Story.new• >> s.name = "ABC"• >> s.link = "http://aaa.com"• >> s.save

Didn’t work?

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Questions?

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