Welcome to Rails
Rails is a web-application framework
that includes everything needed to create database-backed web applications
according to the Model-View-Control pattern.
This pattern splits the view (also called the presentation) into
"dumb" templates that are primarily responsible for inserting
pre-built data in between HTML tags. The model contains the
"smart" domain objects (such as Account, Product, Person, Post)
that holds all the business logic and knows how to persist themselves to a
database. The controller handles the incoming requests (such as Save New
Account, Update Product, Show Post) by manipulating the model and directing
data to the view.
In Rails, the model is handled by
what‘s called an object-relational mapping layer entitled Active
Record. This layer allows you to present the data from database rows as
objects and embellish these data objects with business logic methods. You
can read more about Active Record in files/vendor/rails/activerecord/README.html.
The controller and view are handled by the Action Pack, which handles both
layers by its two parts: Action View and Action Controller. These two
layers are bundled in a single package due to their heavy interdependence.
This is unlike the relationship between the Active Record and Action Pack
that is much more separate. Each of these packages can be used
independently outside of Rails. You
can read more about Action Pack in files/vendor/rails/actionpack/README.html.
Getting Started
- At the command prompt, start a new Rails application using the
rails command and your application name. Ex: rails myapp
- Change directory into myapp and start the web server:
script/server (run with —help for options)
- Go to localhost:3000/ and get
"Welcome aboard: You‘re riding the Rails!"
- Follow the guidelines to start developing your application
Web Servers
By default, Rails will try to use
Mongrel if it‘s are installed when started with script/server,
otherwise Rails will use WEBrick,
the webserver that ships with Ruby. But you can also use Rails with a variety of other web
servers.
Mongrel is a Ruby-based webserver with a C component (which requires
compilation) that is suitable for development and deployment of Rails applications. If you have Ruby
Gems installed, getting up and running with mongrel is as easy as: gem
install mongrel. More info at: mongrel.rubyforge.org
Say other Ruby web servers like Thin and Ebb or regular web servers like
Apache or LiteSpeed or Lighttpd or IIS. The Ruby web servers are run
through Rack and the latter can either be setup to use FCGI or proxy to a
pack of Mongrels/Thin/Ebb servers.
Apache .htaccess example for FCGI/CGI
# General Apache options AddHandler fastcgi-script .fcgi AddHandler
cgi-script .cgi Options +FollowSymLinks +ExecCGI
# If you don‘t want Rails to
look in certain directories, # use the following rewrite rules so that
Apache won‘t rewrite certain requests # # Example: # RewriteCond
%{REQUEST_URI} ^/notrails.* # RewriteRule .* - [L]
# Redirect all requests not available on the filesystem to Rails # By default the cgi dispatcher
is used which is very slow # # For better performance replace the
dispatcher with the fastcgi one # # Example: # RewriteRule ^(.*)$
dispatch.fcgi [QSA,L] RewriteEngine On
# If your Rails application is
accessed via an Alias directive, # then you MUST also set the RewriteBase
in this htaccess file. # # Example: # Alias /myrailsapp
/path/to/myrailsapp/public # RewriteBase /myrailsapp
RewriteRule ^$ index.html [QSA] RewriteRule ^([^.]+)$ $1.html [QSA]
RewriteCond %{REQUEST_FILENAME} !-f RewriteRule ^(.*)$ dispatch.cgi [QSA,L]
# In case Rails experiences terminal
errors # Instead of displaying this message you can supply a file here
which will be rendered instead # # Example: # ErrorDocument 500 /500.html
ErrorDocument 500 "<h2>Application error</h2>Rails application failed to start
properly"
Sometimes your application goes wrong. Fortunately there are a lot of tools
that will help you debug it and get it back on the rails.
First area to check is the application log files. Have "tail -f"
commands running on the server.log and development.log. Rails will automatically display
debugging and runtime information to these files. Debugging info will also
be shown in the browser on requests from 127.0.0.1.
You can also log your own messages directly into the log file from your
code using the Ruby logger class from inside your controllers. Example:
class WeblogController < ActionController::Base
def destroy
@weblog = Weblog.find(params[:id])
@weblog.destroy
logger.info("#{Time.now} Destroyed Weblog ID ##{@weblog.id}!")
end
end
The result will be a message in your log file along the lines of:
Mon Oct 08 14:22:29 +1000 2007 Destroyed Weblog ID #1
More information on how to use the logger is at www.ruby-doc.org/core/
Also, Ruby documentation can be found at www.ruby-lang.org/ including:
These two online (and free) books will bring you up to speed on the Ruby
language and also on programming in general.
Debugger
Debugger support is available through the debugger command when you start
your Mongrel or Webrick server with —debugger. This means that you
can break out of execution at any point in the code, investigate and change
the model, AND then resume execution! You need to install ruby-debug to run
the server in debugging mode. With gems, use ‘gem install
ruby-debug’ Example:
class WeblogController < ActionController::Base
def index
@posts = Post.find(:all)
debugger
end
end
So the controller will accept the action, run the first line, then present
you with a IRB prompt in the server window. Here you can do things like:
>> @posts.inspect
=> "[#<Post:0x14a6be8 @attributes={\"title\"=>nil, \"body\"=>nil, \"id\"=>\"1\"}>,
#<Post:0x14a6620 @attributes={\"title\"=>\"Rails you know!\", \"body\"=>\"Only ten..\", \"id\"=>\"2\"}>]"
>> @posts.first.title = "hello from a debugger"
=> "hello from a debugger"
…and even better is that you can examine how your runtime objects
actually work:
>> f = @posts.first
=> #<Post:0x13630c4 @attributes={"title"=>nil, "body"=>nil, "id"=>"1"}>
>> f.
Display all 152 possibilities? (y or n)
Finally, when you‘re ready to resume execution, you enter
"cont"
Console
You can interact with the domain model by starting the console through
script/console. Here you‘ll have all parts of the
application configured, just like it is when the application is running.
You can inspect domain models, change values, and save to the database.
Starting the script without arguments will launch it in the development
environment. Passing an argument will specify a different environment, like
script/console production.
To reload your controllers and models after launching the console run
reload!
dbconsole
You can go to the command line of your database directly through
script/dbconsole. You would be connected to the database with the
credentials defined in database.yml. Starting the script without arguments
will connect you to the development database. Passing an argument will
connect you to a different database, like script/dbconsole
production. Currently works for mysql, postgresql and sqlite.
Description of Contents
app
Holds all the code that's specific to this particular application.
app/controllers
Holds controllers that should be named like weblogs_controller.rb for
automated URL mapping. All controllers should descend from ApplicationController
which itself descends from ActionController::Base.
app/models
Holds models that should be named like post.rb.
Most models will descend from ActiveRecord::Base.
app/views
Holds the template files for the view that should be named like
weblogs/index.html.erb for the WeblogsController#index action. All views use eRuby
syntax.
app/views/layouts
Holds the template files for layouts to be used with views. This models the common
header/footer method of wrapping views. In your views, define a layout using the
<tt>layout :default</tt> and create a file named default.html.erb. Inside default.html.erb,
call <% yield %> to render the view using this layout.
app/helpers
Holds view helpers that should be named like weblogs_helper.rb. These are generated
for you automatically when using script/generate for controllers. Helpers can be used to
wrap functionality for your views into methods.
config
Configuration files for the Rails environment, the routing map, the database, and other dependencies.
db
Contains the database schema in schema.rb. db/migrate contains all
the sequence of Migrations for your schema.
doc
This directory is where your application documentation will be stored when generated
using <tt>rake doc:app</tt>
lib
Application specific libraries. Basically, any kind of custom code that doesn't
belong under controllers, models, or helpers. This directory is in the load path.
public
The directory available for the web server. Contains subdirectories for images, stylesheets,
and javascripts. Also contains the dispatchers and the default HTML files. This should be
set as the DOCUMENT_ROOT of your web server.
script
Helper scripts for automation and generation.
test
Unit and functional tests along with fixtures. When using the script/generate scripts, template
test files will be generated for you and placed in this directory.
vendor
External libraries that the application depends on. Also includes the plugins subdirectory.
If the app has frozen rails, those gems also go here, under vendor/rails/.
This directory is in the load path.