CSC/ECE 517 Fall 2010/ch2 2d dg

Scaffolding in Web Application Frameworks

Overview

Scaffolding in General

Scaffolding in education is basically the support a teacher gives to a new student to get him started on his subject. Scaffolding is also the temporary structure often used by workers in construction. So what we know of the word scaffolding in real world – a temporary structure to lean on while you build the main structure. The temporary structure can then be discarded.

Scaffolding in Programming

It is with the same basic idea that scaffolding in web programming frameworks refer to. It refers to a temporary structure, which is useful as a starting point for developing an application. Scaffolding is nothing but a basic structure that helps a new programmer to get started quickly. It is meta-programming method to quickly generate a functioning web application with the CRUD functionality. Any web application that interacts with database has 4 basic functions generally called CRUD, which it always needs and these are:

• Create,
• Read,
• Update or
• Delete a record.

A scaffold will generate a functioning web application that allows you to carry out these functions. Usually you get a running web application with not more than a few lines of code. It generates for you what is often termed as boilerplate code. In a MVC framework, scaffolding will usually create basic model, views and controllers and also the database objects needed.

Features of Scaffolding

In software applications, we need to use a number of frameworks to make application run. The frameworks may include:

• Database access
• Screen design, and
• Business rules

And scaffolding is the mechanism by which we can create the skeletal of the web application at first go. So, now after having some basic concept of scaffolding, we can list out the main features of scaffolding below,

• It is a framework that provides the minimal setup of the components like database, application servers, and web servers.
• When you want to use the structure early on in the development cycle when you are experimenting with the database schema and layout, it helps to quickly generate basic functional application for you directly from the database schema.
• Scaffolding helps when the schema undergoes refinement and you don't need to waste your time to change the views and controllers explicitly to align with the change.
• It isn't what you would like to use directly in your production systems, you can eventually make changes as you move on with your added and updated project requirements.

History of Scaffolding

Origin and Evolution

Scaffolding Theory

Scaffolding theory in education came into being in 1950, by, Jerome Bruner, where he described the various scaffolding techniques for oral language and written vocabulary. In Oral scaffolding, parents and adults help the children to make them know how to speak and communicate, how they should use the words and develop the base or a temporary framework for their children to walk in the new world. And once the child secures the control over the things, the support can be taken away. Similarly, in written scaffolding, typical supporting instructions were given by the instructor to the students to learn vocabulary, to calibrate the task, to identify the task and work independently on the task, in this way they built the scaffold for them on which they can lean on while learning. So children use oral scaffolding as a vehicle to communicate and written scaffolding as tool for new thinking. And the teacher’s instructions also get changed from time to time, starting from the directions, to suggestions, to encouragement, and then observation.

Scaffolding Origin in Web Applications

Scaffolding has been around in various forms for some time. Earlier, separate code generators were written, which would generate CRUD functionality for certain frameworks. They were often the third party generators which offered varying capabilities and mainly acted as database code generators.

You could also have custom scripts, which could generate the CRUD screens from some database specifications. Often each new project involved writing up some templates to get the basic functionality or writing a template generator script, which created these templates for a project. But these generators and scripts were non-standardized and often viewed as taking time away from the core development of an application.

What Scaffolding is Today?

Current Scaffolding Scope

Scaffolding is now a part of many web application frameworks. We can find a number of development software’s that uses web application scaffolding approach. Frameworks include,

• Ruby on Rails,
• CakePHP ,
• ASP.NET
• CodeIgniter
• iPhone Web Scaffolding
• Grails

These frameworks actually contain some software components that create the skeletal attachments to the application’s database and other external devices. We will see how this scaffolding works in some of the frameworks described above in next few paragraphs.

Benefits of Scaffolding

We have noticed that scaffolding makes the developers job easier, and rather than making a lot of configuration changes at the very first time or may be at the time of updations, he can concentrate on the business logic of the application, which saves lot of time that he may have spent in creating and maintaining the database code. So you can read out the benefits of Scaffolding below,

• It acts as a tool for the developers to quickly generate running web application environment for the Internet.
• It provides modular stubs to perform typical CRUD implementations.
• It improves development productivity for system architects.
• It improves efficiency by creating reusable components for developers by using frameworks and code generators.

Scaffolding in MVC based Web Frameworks

First we will describe how the scaffolding approach works in Rails framework. Scaffolding gets its popularity with the rails framework only, and it comes as the inbuilt feature of the rails framework.

Scaffolding in Rails Framework

Now lets see how scaffolding in the rails framework helps to create the database schema at the start of an application by using very simple commands. Rails scaffolding helps to create model, view and controllers for the new resource in a single operation. Follow these steps in the Eclipse IDE to create a scaffolding of a car website. We just define some attributes of a car like its color, year and model.

Step -1. Create New Rails Project: New->New Rails Project

Step -2. Get the generator view: Window->Show View->Generators

Step -3. Make sure current project for Generator is the project that you want.

Step -4. Select the scaffold generator from drop down box: Generator->scaffold

Step -5. In parameters, specify the model, fields and their type Here we take, Car color:string maker:string year:date

Step -6. This will run the generate script and create files in View, controllers, model, db etc as shown below:

  >script/generate scaffold Car color:string maker:string model:number year:date

exists app/models/
exists app/controllers/
exists app/helpers/
create app/views/cars
exists app/views/layouts/
exists test/functional/
exists test/unit/
exists test/unit/helpers/
exists public/stylesheets/
create app/views/cars/index.html.erb
create app/views/cars/show.html.erb
create app/views/cars/new.html.erb
create app/views/cars/edit.html.erb
create app/views/layouts/cars.html.erb
create public/stylesheets/scaffold.css
create app/controllers/cars_controller.rb
create test/functional/cars_controller_test.rb
create app/helpers/cars_helper.rb
create test/unit/helpers/cars_helper_test.rb
route  map.resources :cars
dependency model
exists app/models/
exists test/unit/
exists test/fixtures/
create app/models/car.rb
create test/unit/car_test.rb
create test/fixtures/cars.yml
create db/migrate
create db/migrate/20100919144829_create_cars.rb

It creates the db migrate file for the given model. This creates the schema in db/migrate/2002301293_create_cars.rb file

class CreateCars < ActiveRecord::Migration
def self.up
create_table :cars do |t|
t.string :color
t.string :maker
t.number :model
t.date :year
t.timestamps
end
end

def self.down
drop_table :cars

end
end

Step -7 You then run a rake task to actually create the database tables using the migrate file.

Step -8 Now go to Window->Show View->Rake

Step -9 In the Rake window, select migrate task from the drop down box and run it.

You can also right click the

• create_cars.rb file,
• select the rake menu option and
• then select migrate option.

 rake db:migrate

Step -10 You can then go to your sqlite database and check that tables have been created.

Scaffold will always generate the tables in the Development database. With this you now have a functioning application. Start the web server and point your browser to http://localhost:3000/cars (unless you decided to override the defaults). You will be presented with a basic screen showing all the cars and their details. Links to web pages to add, edit and destroy a record are also provided. Using these, you can modify existing records or add new records. Sample auto generated code for the above example is as below.

Controller for car in cars_controller.rb

class CarsController < ApplicationController
  # GET /cars
  # GET /cars.xml
  def index
    @cars = Car.all

    respond_to do |format|
      format.html # index.html.erb
      format.xml  { render :xml => @cars }
    end
  end

  # GET /cars/1
  # GET /cars/1.xml
  def show
    @car = Car.find(params[:id])

    respond_to do |format|
      format.html # show.html.erb
      format.xml  { render :xml => @car }
    end
  end

  # GET /cars/new
  # GET /cars/new.xml
  def new
    @car = Car.new

    respond_to do |format|
      format.html # new.html.erb
      format.xml  { render :xml => @car }
    end
  end

  # GET /cars/1/edit
  def edit
    @car = Car.find(params[:id])
  end

  # POST /cars
  # POST /cars.xml
  def create
    @car = Car.new(params[:car])

    respond_to do |format|
      if @car.save
        format.html { redirect_to(@car, :notice => 'Car was successfully created.') }
        format.xml  { render :xml => @car, :status => :created, :location => @car }
      else
        format.html { render :action => "new" }
        format.xml  { render :xml => @car.errors, :status => :unprocessable_entity }
      end
    end
  end

  # PUT /cars/1
  # PUT /cars/1.xml
  def update
    @car = Car.find(params[:id])

    respond_to do |format|
      if @car.update_attributes(params[:car])
        format.html { redirect_to(@car, :notice => 'Car was successfully updated.') }
        format.xml  { head :ok }
      else
        format.html { render :action => "edit" }
        format.xml  { render :xml => @car.errors, :status => :unprocessable_entity }
      end
    end
  end

  # DELETE /cars/1
  # DELETE /cars/1.xml
  def destroy
    @car = Car.find(params[:id])
    @car.destroy

    respond_to do |format|
      format.html { redirect_to(cars_url) }
      format.xml  { head :ok }
    end
  end
end

Sample view file for EDIT generated in views->cars->edit.html.erb

<h1>Editing car</h1>

<% form_for(@car) do |f| %>
  <%= f.error_messages %>

  <p>
    <%= f.label :color %><br />
    <%= f.text_field :color %>
  </p>
  <p>
    <%= f.label :maker %><br />
    <%= f.text_field :maker %>
  </p>
  <p>
    <%= f.label :model %><br />
    <%= f.text_field :model %>
  </p>
  <p>
    <%= f.label :year %><br />
    <%= f.date_select :year %>
  </p>
  <p>
    <%= f.submit 'Update' %>
  </p>
<% end %>

<%= link_to 'Show', @car %> |
<%= link_to 'Back', cars_path %>

Database migrate file generated in db->migrate

class CreateCars < ActiveRecord::Migration
  def self.up
    create_table :cars do |t|
      t.string :color
      t.string :maker
      t.integer :model
      t.date :year

      t.timestamps
    end
  end

  def self.down
    drop_table :cars
  end
end

Database schema generated in db->schema.rb file

ActiveRecord::Schema.define(:version => 20100919144829) do

  create_table "cars", :force => true do |t|
    t.string   "color"
    t.string   "maker"
    t.integer  "model"
    t.date     "year"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

end

Dynamic Scaffolding in CakePHP

Scaffolding in CakePHP is a little more limited than Rails. Unlike Rails, database tables and schema are created separately in CakePHP. It follows the dynamic scaffolding paradigm where you don't need to run an external command to generate the scaffolded code, what is needed is just to define the $scaffold variable and scaffolding is taken care of.

Steps for code generation in CakePHP

Step -1 Create the database schema and the tables.

Step -2 Each table that has to be scaffolded should have a corresponding controller.

Step -3 That controller must define the variable $scaffold For eg, considering our cars example, lets say we have a cars controller-

<?php
    class CarsController extends AppController
    {
        var $scaffold;
    }
?>

This will go in CarsController.php in app/controllers directory. That is all that is required. The framework will now auto-generate the basic functionality for create, update, delete.

Other Examples

A more detailed listing of examples of scaffolding in various other web frameworks can be found in last year's treatment of the same topic here.

http://pg-server.csc.ncsu.edu/mediawiki/index.php/CSC/ECE_517_Fall_2009/wiki1b_9_ss

See Also

You can go through some of the other frameworks to create scaffold web applications.

1. CakePHP Framework
2. Grails Framework
3. ASP.NET Framework
4. Codeigniter
5. iPhone
6. NetBeans CRUD Generator

Bibiliography

References

1. Programming Ruby(2nd Edition): The Pragmatic Programmers' Guide (Pragmatic Programmers Series), by Dave Thomas, Andy Hunt, Andrew Hunt, Chad Fowler, Chad Fowler: Publisher: Pragmatic Bookshelf
2. Agile Web Development with Rails, 3rd ed. by Dave Thomas, David Heinemeier Hansson, David Hansson, Publisher: Pragmatic Bookshelf
3. http://msdn.microsoft.com/en-us/library/cc488469.aspx
4. http://guides.rubyonrails.org/getting_started.html

External Sites

1. http://en.wikipedia.org/wiki/Scaffolding_Theory
2. http://www.wisegeek.com/what-is-web-application-scaffolding.htm
3. http://www.developer.com/lang/php/article.php/3636686/Scaffolding-with-CakePHP---Managing-Your-Fantasy-Football-Team.htm
4. http://cpan.uwinnipeg.ca/htdocs/Scaffold/Scaffold.html

MediaSite

1. http://www.asp.net/aspnet-in-net-35-sp1/videos/getting-started-with-dynamic-data
2. http://www.youtube.com/watch?v=zV6aueUh8Bs
3. http://www.youtube.com/watch?v=LWoCfTyWG_E