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Making XML in a Rails App

January 17, 2007

Ruby on Rails is a database-based web framework. An XML document may be created and parsed with Ruby on Rails. Rails provides a Ruby library called Builder to generate XML markup. The Builder package contains class Builder::XmlMarkup to generate an XML document. In this article, we will create an XML document from a database table with the Builder library.

Installing XML Builder

Before installing Builder, we need to install the Ruby on Rails framework and RubyGems, the standard Ruby package manager. Download the Ruby Windows Installer application and double-click the ruby185-21.exe application. When Ruby Setup Wizard gets started, click on Next and accept the license agreement. Select the default components to install, including the RubyGems package manager. Specify a directory to install Ruby (c:/ruby is the default) and click Next. Specify a Start menu folder and click on Install to install Ruby and RubyGems. Next, install Rails. From the c:/ruby directory--the directory in which Ruby is installed--run the following command to install Rails and dependencies.

c:/ruby>gem install rails --include-dependencies

Builder is included with the package manager RubyGems. Run the following command to install Builder 2.0.0.

C:/ruby>gem install builder

The Builder::XmlMarkup class provides the methods discussed in Table 1.

Method Description
cdata!(text) Adds a CDATA section.
comment!(comment_text) Adds a comment.
declare!(inst, *args, &block) Adds a declaration. args specifies 0 or more arguments.
instruct!(directive_tag=:xml, attrs={}) Adds a processing instruction. Attributes are specified with an array of hash entries.
new(options={}) Creates an XML markup Builder object. The following options may be specified in an array of hash entries. :target=>targetObject:indent=>indentation :margin=>initial_indentation
target!() Returns target of Builder object.
Table 1. Builder::XmlMarkup methods

We also need to install the MySQL database for creating an XML document from the database. Download MySQL 5.0. Install MySQL 5.0 with Setup.exe and create a MySQL Server instance.

Creating an XML Document from a Database

In this section we will create an XML document from a database table. Create a Rails application for generating an XML document from a database:

C:/ruby>rails databasexml

Modify the development mode settings in the app/config/database.yml file to specify the database as test. The development mode settings for the MySQL database are shown in the following listing.

development:  
adapter: mysql 
database: test  
username: root  
password: nil 
host: localhost

We will use ActiveRecord migrations to create a database table. Create a migration script by creating a model script with the following Ruby command:

C:\ruby\databasexml> ruby script/generate 
model catalog

A model script app/models/catalog.rb and a migration script db/migrate/001_create_catalogs.rb are created. The migration script class, CreateCatalogs, extends the ActiveRecord::Migration class as shown in the following listing:

class CreateCatalogs < ActiveRecord::Migration
  def self.up
    create_table :catalogs do |t|
      # t.column :name, :string
    end
  end

  def self.down
    drop_table :catalogs
  end
end

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