Web applications with Ruby and Rails
On the Right Track
Armin Röhrland and Stefan Schmiedl
Web applications with Ruby and RailsOn the Right TrackArmin Röhrland and Stefan Schmiedl |
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Web development is often characterized by quick and dirty hacks with a colorful mixture of program code and HTML. However, an effort is underway to bring a more formal structure to web programming. For example, Rails [1] uses Ruby to implement a classical Model View Controller (MVC) framework, something that the world of smalltalk has used for some time. The MVC framework abstracts the data processing in the model from the GUI-based manipulation code (controller) and the representation code (view), see Figure 1.
This technique of abstracting the data from the data processing methods can be applied to anything from a database table to a workflow model for a large-scale enterprise. The model is partly or completely visualized in the view. Controllers react to user input (among other things) to initiate status changes within the model.
| The Author |
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Armin Röhrl and Stefan Schmiedl run a company called agile Software-schmiede Approximity GmbH. They have been using Ruby for five years now, and they still have fun working with Ruby and other hyper-productive project development and management solutions. Productivity is more important to the authors than the latest hype. |
This structure makes the application logic independent of the external representation and user interface. Some development products claim to support MVC, although this support typically turns out to be two thirds hot air on closer inspection.
Rails includes the Active Record, which provides object relational mapping, to support the model. The Action Pack model subdivides web requests into controller and view-specific components. This design makes Rails really useful for developing database based Web applications, such as the project management software Basecamp [2], which was programmed using Rails. (See the box titled "Interview with the Rails Author.") When you work with Rails, you can tell the design of system comes from a practical background. Rails avoids many of the pitfalls present in more theoretical frameworks.
Rails is based on the DRY concept (Don't Repeat Yourself - in other words, "once and only once.") Repeat code within a program smacks of bad program design.
Rails tends to use reflection and runtime modules to replace configuration files; this removes the need for a typical XML-style configuration marathon. It also has the effect of applying changes immediately without having to go through a time-consuming build process.
Rails also has integrated functionality for general and unit tests. RubyDoc provides documentation. The big advantage is that all three components of the MVC framework were written in Ruby.
If developers stick to the Rails conventions (mapping between database and object structures), so called scaffolding helps to put a project online in next to no time. Functions for adding, modifying, and deleting objects are available at the click of a button.
Our sample application is based on the tutorial from the Ruby homepage. We will create a simple Web application in the folder /var/www/railsdemo. Rails starts by creating a scaffold containing the required files:
rails /var/www/railsdemo
This command will overwrite an existing Rails application in the specified directory, so proceed with caution. We need a MySQL database for the sample table; see Listing 1.
The Yaml file config/database.yml defines access to the database; the file serializes data in a language-independent format:
production: adapter: mysql database: rails_production host: localhost username: root password:
The entry for the test database looks similar to this. In real life, you will not want to run this with root privileges that are without a password.
The new_controller script creates a new controller; its name should start with a capital letter. The views follow the controller name:
./script/new_controller U Friends list display new edit
Avoid using process as a view name, as Rails uses this name for internal purposes. The process for creating a new model is similar:
./script/new_model U Person
Rails typically discovers the underlying database table automatically. If required, the script will accept a table name after the model name:
./script/new_model U Person people
To test the configuration of the Rails application, developers should run rake (Ruby make) in the application directory. A number of issues can occur depending on your system configuration:
To complete the Web application, we now need to provide some content for app/views/friends/display.rhtml:
01 <html> 02 <body> 03 <h1>Friends#display</h1> 04 <p>Displays a person entry</p> 05 <p> 06 <%= @person.name %><br /> 07 <%= @person.street1 %><br /> 08 <%= @person.street2 %><br /> 09 <%= @person.city %><br /> 10 <%= @person.state %><br /> 11 <%= @person.zip %><br /> 12 </p> 13 </body> 14 </html>
This looks similar to Erb, the HTML embedded Ruby variant. The HTML page displays the data that the model provides. The control has to define and create the @person object referenced here. This occurs in the app/controllers/friends_controller.rb file, which contains the access methods. The require keyword adds the model:
require 'person'
The Web application can now use the Active Record class to access the database. If we now insert the following code for the display method, it will get the first entry from the table and write it to the @person instance variable for the view class:
def display @person = Person.find(1) end
The model class definition in app/models/person.rb is also worth examining:
require 'active_record' class Person < U ActiveRecord::Base end
| Listing 1: SQL for Person |
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01 CREATE DATABASE rails_production; 02 USE rails_production; 03 04 CREATE TABLE people ( 05 id int(10) unsigned NOT NULL auto_increment, 06 name varchar(50) NOT NULL default '', 07 street1 varchar(70) NOT NULL default '', 08 street2 varchar(70) NOT NULL default '', 09 city varchar(70) NOT NULL default '', 10 state char(2) NOT NULL default '', 11 zip varchar(10) NOT NULL default '', 12 PRIMARY KEY (id), 13 KEY name (name) 14 ) TYPE=MyISAM AUTO_INCREMENT=2 ; 15 16 INSERT INTO people VALUES (1, 'Superman', 17 '123 Somewhere', '', 'Smallville', 'KS', '123456') |
| Table 1: Java and Ruby | ||
| Application | Java | Ruby |
| Application GUI | Swing | TK, QT, Fox |
| Web GUI | JSP, XSLT, XMLC... | Iowa, Rails |
| Persistent Domain Objects | Entity EJBs, JDO, manual | Kansas |
| and Transaction Management | generated DAOs & | |
| RPC Mechanism (Remote Pro- | Session EJBs, Servlets | DRb |
| cedure Call) for communication | ||
| between front-end and back-end | ||
| Infrastructure for asynchronous communication | Message-Driven EJBs | DRb/Rinda/Tupleserver |
The base class ActiveRecord::Base does most of the work, as it defines simple methods of access to the database. The table name is the plural of the class name. Interestingly, the plural form is grammatically correct for irregular nouns, for example, men for man or people for person. Refer to the class documentation for more detail on naming rules and conventions [8].
The results of all this work are now visible under http://localhost/rails/friends/display. This URL points at the controller (friends) and at the action (display).
| Box 1: Installation |
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For users of Mac OS X (version 10.3 or newer), two videos [5] demonstrate the installation process. Of course, they are interesting for Linux users too. Rubygems [6] (version 0.7 or newer), a packet management tool for Ruby, provides a simple approach to installing:
gem install rails Whenever a new version of Action Pack or Active Record is released, you can update simply by typing gem update. Make sure the database connection to the back-end is available; you can use either MySQL or PostgreSQL. Debian users will need to fulfill a few requirements for the install, as the required components are spread across a large number of packets (see also [7]): irb1.8, libbigdecimal-ruby1.8, libdbm-ruby1.8, libdl-ruby1.8, libdrb-ruby1.8, liberb-ruby1.8, libgdbm-ruby1.8, libiconv-ruby1.8, libopenssl-ruby1.8, libpty-ruby1.8, libracc-runtime-ruby1.8, libreadline-ruby1.8, librexml-ruby1.8, libruby1.8, libruby1.8-dbg, libsdbm-ruby1.8, libsoap-ruby1.8, libstrscan-ruby1.8, libsyslog-ruby1.8, libtest-unit-ruby1.8, libwebrick-ruby1.8, libxmlrpc-ruby1.8, libyaml-ruby1.8, libzlib-ruby1.8, rdoc1., ri1.8 ruby1.8, ruby1.8-dev, ruby1.8-elisp, and finally, ruby1.8-examples.
Setting Up ApacheIf you have not done so already, you need to enable the Apache rewrite module:
# a2enmod Which module would you like to enable? Your choices are: ... rewrite ... Module name? rewrite Module rewrite installed; run /etc/init.d/apache2 force-reload to enable. To run a Rails application in /var/www/myapp, you need to add an entry for the virtual host to your Apache configuration file. The entry would look something like this:
01 <VirtualHost *:80> 02 ServerName rails 03 DocumentRoot /var/www/railsdemo/public 04 ErrorLog /var/www/railsdemo/log/apache.log 05 <Directory/var/www/railsdemo/public/> 06 Options ExecCGI FollowSymLinks 07 AllowOverride all 08 Order allow,deny 09 Allow from all 10 </Directory> 11 </VirtualHost> Check the htaccess file for the Web application for more settings; in our example this is /var/www/railsdemo/public/.htaccess. Now, working as root, reload your Apache configuration as follows to apply the updates:
/etc/init.d/apache2 force-reload |
Rails also has a solution for associating tables. We will use two tables with phone number (see Listing 2).
Rails uses a suffix (_id) to identify external keys, for example person_id. As previously mentioned, the table name is the plural form of the model name:
./script/new_model Phone
The file generated previously, person.rb needs two modifications:
require 'active_record'
require 'phone'
class Person < U
ActiveRecord::Base
has_many :phones
end
The call has_many :phones specifies a 1:n relationship. In other words, a person can have more than one phone number. We need to add the following lines to display.html to change the display format:
<% for phone in U @person.phones %> <%= phone.phone %><br/> <% end %>
If a model already exists, it is quite easy to use scaffolding techniques in Rails to define display and manipulation methods for the data. Web developers can then fine-tune the basic methods as required.
The following example assumes an empty Rails application directory. We will be creating a controller and a model first (./script/new _controller Friend and ./script_new _model Person, see above.) Make sure you do not have an action called list. Rails will use the existing database. We simply need to modify the friends controller:
scaffold :person
This addition creates new methods with default behavior, as specified in the documentation at [9]: list, show, destroy, new, create, edit, and update.
This supports scaffolding with the Person, but we still need the phone numbers. To avoid name collisions when defining the telephone actions, Rails adds an action reference to the model name if you set the right flags:
scaffold :person, :suffixU => true scaffold :phone, :suffixU => true
This gives us the following URLs:
http://rails/friends/list_person http://rails/friends/list_phone
As you can see, we have created a structured Web application with a minimum of effort. The application will store and manipulate objects in a relational database. Ruby implements the MVC model neatly, and Ruby even generates the basic code associated with the MVC structure.
| Listing 2: SQL for Telephone Numbers |
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01 USE rails_production; 02 CREATE TABLE phones ( 03 id int(10) unsigned NOT NULL auto_increment, 04 person_id int(10) unsigned NOT NULL default '0', 05 phone varchar(15) NOT NULL default '', 06 PRIMARY KEY (id), 07 KEY people_id (person_id), 08 KEY phone (phone) 09 ) TYPE=MyISAM AUTO_INCREMENT=3 ; 10 11 INSERT INTO phones VALUES (1, 1, '1234567890'); 12 INSERT INTO phones VALUES (2, 1, '1122334455'); |
Rails makes it easier to develop basic applications if you stick to the rules. The system provides an extremely useful introduction to programming web applications. If you need more help getting started with Ruby, check out the Ruby Manual.
| Box 2: An Interview with Rails Developer, David Heinemeier Hansson |
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LM: Why did you develop Rails? DH: I had been programming in PHP for a few years while keeping a close eye on all the web-related projects in Java. I loved PHP for its immediacy and was very inspired by the frameworks in Java. So I didn't want to give up the quick turn-around from PHP, but neither was I willing to suffer under the problems it had with large, object-oriented systems. Right around the height of my annoyance with PHP, and not long after a disillusioning meeting with Java (worked in a J2EE shop for 6-7 months), I read about how Martin Fowler and the Pragmatic Programmers were really into this niche language. That language was of course Ruby, and once I climbed the initial stumbling blocks, it was just love, love, love from there on. Putting all my inspirations from Java into a framework carried by Ruby proved to be a very natural path for me. Oh, and I needed to do it anyway in order to build Basecamp as quickly as we did (in two man-months). LM: What is the biggest strength of Rails? DH: Clean immediacy. You can create applications incredibly quickly that won't result in a code mess. Build one quickly to keep. A strong focus on proven patterns, such as test- and domain-driven development, along with an MVC division really helps here. LM: What is the biggest weakness of Rails? DH: IIt can be hard to convince prospective clients (or your manager) that they should let you be productive in a relatively unknown language when all they read about is Java and C#. LM: What is the future of Rails? DH: Hopefully, a 1.0 release within the year 2004. I think 2005 could really be The Year of Ruby, and I'm hoping the release of Rails will help ensure that. But otherwise, I have pretty humble goals for the further development of the framework. Rails is currently around 2,500 lines of code. I'd like it not to grow much larger than that. LM: Please tell us 2 paragraphs on Basecamp. Maybe you could also mention the business model. DH: Basecamp is a web-based project management application built around weblogs, milestones, and todo lists. It's a deceivingly simple application that has had a huge impact on how many people manage their projects. It's a hosted application that firms pay between $19 and $59 a month to use. There's even a lifetime free 1-project plan, if you just want to try it out. LM: What is the future of basecamp? DH: We're continuously improving the application. Just last week we launched a whole slew of new features to better manage the responsibilities on a project. Also, I think we've just tapped a tiny percentage of a huge market. Project management is everywhere. Besides the obvious uses in businesses, we're seeing people use Basecamp to plan everything from home improvement initiatives to weddings. Basecamp is a great fit for such a wide range of projects because of its simplicity. Managing the project is not a project in itself. LM: Where do you think web-based programming is leading? DH: I hope it's away from the intense complexity that J2EE, .NET, and other heavy-handed environments have somehow convinced people they need. Dynamic languages such as Ruby and the frameworks built around them, like Rails, are going to sweep the scene in the coming years. Customers and developers will begin to realize that most web-applications doesn't need the firepower of an Imperial star destroyer, but rather the flexibility of an X-wing (yeah, I just watched Star Wars on DVD). |
| Info |
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[1] Ruby on Rails: http://www.rubyonrails.org [2] Basecamp: http://www.basecamphq.com [3] Apache Struts: http://struts.apache.org [4] Struts Action Invocation Framework (SAIF): http://struts.sourceforge.net/saif/ [5] Tutorial videos: http://www. rubyonrails.org/show/HomePage [6] Rubygems: http://rubygems.rubyforge.org/wiki/wiki.pl [7] Rails for Debian: http://www.rubyonrails.org/show/RailsOnDebian [8] Rules for plural names: http://api.rubyonrails.org/classes/ActiveRecord/Base.html [9] Scaffolding methods: http://api.rubyonrails.org/classes/ActionController/Scaffolding/ClassMethods.html [10] The Rail author's weblog: http://loudthinking.com |