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14.1 Origins and Uses of Ruby
- Designed by Yukihiro Matsumoto; released in
1996
- Use spread rapidly in Japan
- Use is now growing in part because of its use in
Rails
- A pure object-oriented purely interpreted
scripting language
- Related to Perl and JavaScript, but not closely
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15.1 Overview of Rails
- Rails is a development framework for Web-based
applications
- Rails is written in Ruby and uses Ruby for its
applications - Ruby on Rails (RoR)
- Based on MVC architecture for applications
- MVC cleanly separates applications into three
parts:
- Model – the data and any restraints on it
- View – prepares and presents results to the
user
- Controller – controls the application
- One characterizing part of Rails is its approach
to connecting object-oriented software with a
relational database – ORM
- Maps tables to classes, rows to objects, and
columns to fields of the objects
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Architecture of a Four-Tier
Application
Supporting
Software
App User
Interface
User Interface
Application Logic
Database Engine
DBMS / Database
Server
Database
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Application Server
Database API
Architecture of a Four-Tier Application
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Architecture of a Four-Tier
Application
Supporting
Software
View
User Interface
Control
T
O
M
C
A
T
Database Engine
Database
Model
MySQL
Rails
ROR MVC Architecture
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15.1 Overview of Rails (continued)
- View documents are XHTML documents that may
include Ruby code
- Most of the controller code is provided by Rails
- A Rails application is a program that provides a
response when a client browser connects to a
Rails-driven Web site
- Rails can be used with Ajax
- Two fundamental principles that guided the
development of Rails:
1. DRY
2. Convention over configuration
- Rails does not use a GUI
- One simple way to get started with Rails is to
download a complete development system
http://instantrails.rubyforge.org/wiki/wiki.pl
- Includes Ruby, Rails, MySQL, Apache and
everything else that is necessary
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15.2 Document Requests (continued)
- Static Documents (continued)
- Next, build the view file, or template, which must
reside in the say subdirectory of the views
directory of the application and be named
hello.html.erb
- This is an XHTML document with the
following in its body element
<h1> Hello from Rails! </h1>
- To test the application, a Web server must be
started
>ruby script/server
- This starts the default server, named Mongrel
- Now, pointing the browser to the application
produces the displayed view template content
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15.2 Document Requests (continued)
- Dynamic Documents
- Dynamic documents can be built with Rails by
embedding Ruby code in the template document
- An example: display a greeting and the current
date and time and the number of seconds since
midnight
- Ruby code is embedded in a document by
placing it between <% and %>
- To insert the result of evaluating the code into
the document, use <%=
- The Time class has a method, now, that returns
the current day of the week, month, day of the
month, time, time zone, and year, as a string
It is now <%= t = Time.now %>
Number of seconds since midnight:
<%= t.hour * 3600 + t.min * 60 + t.sec %>
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15.3 Rails Applications with
Databases
- We will use MySQL
- Use a simple database with just one table
- The application will be named cars
- The application will present a welcome document
to the user, including the number of cars in the
database and a form to get the beginning and
ending years and a body style for the desired car
- Creating the application
- In the subdirectory of our examples:
>rails –d mysql cars
- It is customary to use three databases in a Rails
database application: one for development, one
for testing, and one for production
- To create the three (empty) databases:
>rake db:create:all
- Creates the database.yml file in the config
subdirectory of the application directory (cars)
- See next page
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15.3 Rails Applications with
Databases (continued)
- If we fill out the form, as in:
- Now we click Create, which produces:
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15.3 Rails Applications with
Databases (continued)
<h1>Listing corvettes</h1>
<table>
<tr>
<th>Body style</th>
<th>Miles</th>
<th>Year</th>
</tr>
<% for corvette in @corvettes %>
<tr>
<td><%=h corvette.body_style %></td>
<td><%=h corvette.miles %></td>
<td><%=h corvette.year %></td>
<td><%= link_to 'Show', corvette %></td>
<td><%= link_to 'Edit',
edit_corvette_path(corvette) %></td>
<td><%= link_to 'Destroy', corvette,
:confirm => 'Are you sure?',
:method => :delete %></td>
</tr>
<% end %>
</table>
<br />
<%= link_to 'New corvette', new_corvette_path %>
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