This guide is designed for beginners who want to get started with a Rails application from scratch. It does not assume that you have any prior experience with Rails. However, to get the most out of it, you need to have some prerequisites installed:

• The Ruby language version 1.8.7 or higher

• The RubyGems packaging system
  • If you want to learn more about RubyGems, please read the RubyGems User Guide
• A working installation of the SQLite3 Database

Rails is a web application framework running on the Ruby programming language. If you have no prior experience with Ruby, you will find a very steep learning curve diving straight into Rails. There are some good free resources on the internet for learning Ruby, including:

• Mr. Neighborly’s Humble Little Ruby Book
• Programming Ruby
• Why’s (Poignant) Guide to Ruby

Also, the example code for this guide is available in the rails github:https://github.com/rails/rails repository in rails/railties/guides/code/getting_started.

Rails is a web application development framework written in the Ruby language. It is designed to make programming web applications easier by making assumptions about what every developer needs to get started. It allows you to write less code while accomplishing more than many other languages and frameworks. Experienced Rails developers also report that it makes web application development more fun.

Rails is opinionated software. It makes the assumption that there is a “best” way to do things, and it’s designed to encourage that way – and in some cases to discourage alternatives. If you learn “The Rails Way” you’ll probably discover a tremendous increase in productivity. If you persist in bringing old habits from other languages to your Rails development, and trying to use patterns you learned elsewhere, you may have a less happy experience.

The Rails philosophy includes several guiding principles:

• DRY – “Don’t Repeat Yourself” – suggests that writing the same code over and over again is a bad thing.
• Convention Over Configuration – means that Rails makes assumptions about what you want to do and how you’re going to do it, rather than requiring you to specify every little thing through endless configuration files.
• REST is the best pattern for web applications – organizing your application around resources and standard HTTP verbs is the fastest way to go.

At the core of Rails is the Model, View, Controller architecture, usually just called MVC. MVCbenefits include:

• Isolation of business logic from the user interface
• Ease of keeping code DRY
• Making it clear where different types of code belong for easier maintenance

A model represents the information (data) of the application and the rules to manipulate that data. In the case of Rails, models are primarily used for managing the rules of interaction with a corresponding database table. In most cases, each table in your database will correspond to one model in your application. The bulk of your application’s business logic will be concentrated in the models.

Views represent the user interface of your application. In Rails, views are often HTML files with embedded Ruby code that perform tasks related solely to the presentation of the data. Views handle the job of providing data to the web browser or other tool that is used to make requests from your application.

Controllers provide the “glue” between models and views. In Rails, controllers are responsible for processing the incoming requests from the web browser, interrogating the models for data, and passing that data on to the views for presentation.

Rails ships as many individual components. Each of these components are briefly explained below. If you are new to Rails, as you read this section, don’t get hung up on the details of each component, as they will be explained in further detail later. For instance, we will bring up Rack applications, but you don’t need to know anything about them to continue with this guide.

• Action Pack
  • Action Controller
  • Action Dispatch
  • Action View
• Action Mailer
• Active Model
• Active Record
• Active Resource
• Active Support
• Railties

Action Pack is a single gem that contains Action Controller, Action View and Action Dispatch. The “VC” part of “MVC”.

Action Controller is the component that manages the controllers in a Rails application. The Action Controller framework processes incoming requests to a Rails application, extracts parameters, and dispatches them to the intended action. Services provided by Action Controller include session management, template rendering, and redirect management.

Action View manages the views of your Rails application. It can create both HTML and XML output by default. Action View manages rendering templates, including nested and partial templates, and includes built-in AJAX support. View templates are covered in more detail in another guide calledLayouts and Rendering.

Action Dispatch handles routing of web requests and dispatches them as you want, either to your application or any other Rack application. Rack applications are a more advanced topic and are covered in a separate guide called Rails on Rack.

Action Mailer is a framework for building e-mail services. You can use Action Mailer to receive and process incoming email and send simple plain text or complex multipart emails based on flexible templates.

Active Model provides a defined interface between the Action Pack gem services and Object Relationship Mapping gems such as Active Record. Active Model allows Rails to utilize other ORMframeworks in place of Active Record if your application needs this.

Active Record is the base for the models in a Rails application. It provides database independence, basic CRUD functionality, advanced finding capabilities, and the ability to relate models to one another, among other services.

Active Resource provides a framework for managing the connection between business objects and RESTful web services. It implements a way to map web-based resources to local objects with CRUDsemantics.

Active Support is an extensive collection of utility classes and standard Ruby library extensions that are used in Rails, both by the core code and by your applications.

Railties is the core Rails code that builds new Rails applications and glues the various frameworks and plugins together in any Rails application.

Rest stands for Representational State Transfer and is the foundation of the RESTful architecture. This is generally considered to be Roy Fielding’s doctoral thesis, Architectural Styles and the Design of Network-based Software Architectures. While you can read through the thesis, REST in terms of Rails boils down to two main principles:

• Using resource identifiers such as URLs to represent resources.
• Transferring representations of the state of that resource between system components.

For example, the following HTTP request:

DELETE /photos/17

would be understood to refer to a photo resource with the ID of 17, and to indicate a desired action – deleting that resource. REST is a natural style for the architecture of web applications, and Rails hooks into this shielding you from many of the RESTful complexities and browser quirks.

If you’d like more details on REST as an architectural style, these resources are more approachable than Fielding’s thesis:

• A Brief Introduction to REST by Stefan Tilkov
• An Introduction to REST (video tutorial) by Joe Gregorio
• Representational State Transfer article in Wikipedia
• How to GET a Cup of Coffee by Jim Webber, Savas Parastatidis & Ian Robinson

The best way to use this guide is to follow each step as it happens, no code or step needed to make this example application has been left out, so you can literally follow along step by step. You can get the complete code here.

By following along with this guide, you’ll create a Rails project called blog, a (very) simple weblog. Before you can start building the application, you need to make sure that you have Rails itself installed.

In most cases, the easiest way to install Rails is to take advantage of RubyGems:

To verify that you have everything installed correctly, you should be able to run the following:

If it says something like “Rails 3.1.3” you are ready to continue.

To begin, open a terminal, navigate to a folder where you have rights to create files, and type:

This will create a Rails application called Blog in a directory called blog.

After you create the blog application, switch to its folder to continue work directly in that application:

The ‘rails new blog’ command we ran above created a folder in your working directory called blog. The blog folder has a number of auto-generated folders that make up the structure of a Rails application. Most of the work in this tutorial will happen in the app/ folder, but here’s a basic rundown on the function of each of the files and folders that Rails created by default:

Just about every Rails application will interact with a database. The database to use is specified in a configuration file, config/database.yml. If you open this file in a new Rails application, you’ll see a default database configured to use SQLite3. The file contains sections for three different environments in which Rails can run by default:

• The development environment is used on your development/local computer as you interact manually with the application.
• The test environment is used when running automated tests.
• The production environment is used when you deploy your application for the world to use.

Rails comes with built-in support for SQLite3, which is a lightweight serverless database application. While a busy production environment may overload SQLite, it works well for development and testing. Rails defaults to using an SQLite database when creating a new project, but you can always change it later.

Here’s the section of the default configuration file (config/database.yml) with connection information for the development environment:

If you choose to use MySQL instead of the shipped SQLite3 database, yourconfig/database.yml will look a little different. Here’s the development section:

If your development computer’s MySQL installation includes a root user with an empty password, this configuration should work for you. Otherwise, change the username and password in thedevelopment section as appropriate.

If you choose to use PostgreSQL, your config/database.yml will be customized to use PostgreSQL databases:

If you choose to use SQLite3 and are using JRuby, your config/database.yml will look a little different. Here’s the development section:

If you choose to use MySQL and are using JRuby, your config/database.yml will look a little different. Here’s the development section:

Finally if you choose to use PostgreSQL and are using JRuby, your config/database.yml will look a little different. Here’s the development section:

Change the username and password in the development section as appropriate.

Now that you have your database configured, it’s time to have Rails create an empty database for you. You can do this by running a rake command:

This will create your development and test SQLite3 databases inside the db/ folder.

One of the traditional places to start with a new language is by getting some text up on screen quickly. To do this, you need to get your Rails application server running.

You actually have a functional Rails application already. To see it, you need to start a web server on your development machine. You can do this by running:

This will fire up an instance of the WEBrick web server by default (Rails can also use several other web servers). To see your application in action, open a browser window and navigate tohttp://localhost:3000. You should see Rails’ default information page: