Rails 3 敏捷Web开发指南(第4版)

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"《应用Rails进行敏捷Web开发(第4版)》是关于使用Ruby on Rails框架进行敏捷Web开发的专业书籍，由S. Ruby、D. Thomas和D. H. Hansson共同撰写。该书主要面向Rails 3版本，但请注意，Rails核心团队持续更新，新版本可能引入与早期版本不兼容的变更。为了运行书中提供的示例，读者需要按照第一章“安装Rails”中的指导安装正确的Rails版本，并可以通过命令行输入`rails -v`来检查当前Rails的版本。若要了解影响本书内容的Rails变更，可访问http://www.pragprog.com/wikis/wiki/ChangesToRails获取最新信息。此书得到了Rails核心团队成员Mikel Lindsaar的高度评价，他推荐该书作为新手Rails开发者入门的首选读物。" 在《应用Rails进行敏捷Web开发(第4版)》中，作者深入浅出地介绍了Ruby on Rails这一强大的Web开发框架，旨在帮助开发者以敏捷的方式构建高效、可扩展的Web应用程序。Rails遵循“约定优于配置”的原则，极大地简化了开发流程，使得开发者能够更专注于业务逻辑而非底层细节。本书的核心知识点包括： 1. **Rails框架基础**：涵盖了Rails的基本架构，如MVC（模型-视图-控制器）模式，以及路由、模型、控制器、视图等关键组件的使用。 2. **ActiveRecord**：详细讲解了Rails内置的ORM（对象关系映射）系统，如何通过ActiveRecord类操作数据库，建立数据模型，执行CRUD（创建、读取、更新、删除）操作。 3. **数据库集成**：包括SQLite、MySQL、PostgreSQL等常见数据库的集成，以及数据库迁移（migrations）的使用，以管理数据库结构的演变。 4. **Rails生成器**：介绍如何使用Rails的scaffold、generate等命令快速生成代码，加速开发进程。 5. **测试驱动开发(TDD)**：阐述如何使用RSpec、Capybara等工具进行单元测试和集成测试，确保代码质量。 6. **Rails的安全性**：涵盖认证、授权、防止XSS和CSRF攻击等方面，确保应用程序的安全。 7. **Ajax与JSON**：讨论如何利用Ajax技术实现页面的无刷新更新，以及与JSON数据交互，提升用户体验。 8. **部署与维护**：讲解如何将Rails应用部署到各种环境，如Heroku、AWS等，并进行性能优化和故障排查。 9. **Rails社区和生态系统**：介绍Rails社区的重要资源、插件和工具，如Gems（Ruby的包管理器）和Rails最佳实践。 10. **版本管理与持续集成**：使用Git进行版本控制，以及Jenkins、Travis CI等工具进行持续集成，保证项目的稳定性和协作效率。通过阅读本书，开发者不仅可以掌握Rails框架的核心知识，还能了解到敏捷开发的实践方法，提升开发速度和项目管理能力。对于初学者来说，这是一本理想的Rails学习指南，对于经验丰富的开发者，它也提供了有价值的参考和深入理解Rails的机会。

Introduction

Ruby on Rails is a framework that makes it easier to develop, deploy, and

maintain web applications. During the months that followed its initial release,

Rails went from being an unknown toy to being a worldwide phenomenon, and

more important, it has become the framework of choice for the implementation

of a wide range of so-called W e b 2.0 applications.

Why is that?

Rails Simply F e e l s Right

First, a large number of developers were frustrated with the technologies they

were using to create web applications. It didn’t seem to matter whether they

were using Java, PHP, or .NET—there was a growing sense that their job was

just too damn hard. And then, suddenly, along came Rails, and Rails was

easier.

But easy on its own doesn’t cut it. W e ’ r e talking about professional developers

writing real-world websites. They wanted to feel that the applications they

were developing would stand the test of time—that they were designed and

implemented using modern, professional techniques. So, these developers dug

into Rails and discover ed it wasn’t just a tool for hacking out sites.

For example, all Rails applications are implemented using the Model-View-

Controller (MVC) architecture. Java developers are used to frameworks such

as Tapestryand Struts, which are based on MVC. But Rails takes MVC further:

when you develop in Rails, you start with a working application, there’s a

place for each piece of code, and all the pieces of your application interact in a

standard way.

Professional programmers write tests. And again, Rails delivers. All Rails appli-

cations have testing support baked right in. As you add functionality to the

code, Rails automatically creates test stubs for that functionality. The frame-

work makes it easy to test applications, and as a result, Rails applications

tend to get tested.

RAILSSIMPLYFEELSRIGHT 17

Rails applications are written in Ruby, a modern, object-oriented scripting

language. Ruby is concise without being unintelligibly terse—you can express

ideas naturally and cleanly in Ruby code. This leads to programs that are easy

to write and (just as important) are easy to read months later.

Rails takes Ruby to the limit, extending it in novel ways that make a pro-

grammer’s life easier. This makes our programs shorter and more readable.

It also allows us to perform tasks that would normally be done in external

conﬁguration ﬁles inside the codebase instead. This makes it far easier to see

what’s happening. The following code deﬁnes the model class for a project.

Don’t worry about the details for now. Instead, just think about how much

information is being expressed in a few lines of code.

class Project < ActiveRecord::Base

belongs_to :portfolio

has_one :project_manager

has_many :milestones

has_many :deliverables, :through => :milestones

validates :name, :description, :presence => true

validates :non_disclosure_agreement, :acceptance => true

validates :short_name, :uniqueness => true

end

Two other philosophical underpinnings keep Rails code short and readable:

DRY and convention over conﬁguration. DRY stands for don’t r e p e a t yourself :

every piece of knowledge in a system should be expressed in just one place.

Rails uses the power of Ruby to bring that to life. Y o u ’ l l ﬁnd very little duplica-

tion in a Rails application; you say what you need to say in one place—a place

often suggested by the conventions of the MVC architecture—and then move

on. For programmers used to other web frameworks, where a simple change

to the schema could involve them in half a dozen or more code changes, this

was a revelation.

Convention over conﬁguration is crucial, too. It means that Rails has sensi-

ble defaults for just about every aspect of knitting together your application.

Follow the conventions, and you can write a Rails application using less code

than a typical Java web application uses in XML conﬁguration. If you need to

override the conventions, Rails makes that easy, too.

Developers coming to Rails found something else, too. Rails isn’t playing catch-

up with the new de facto web standards; it’s helping deﬁne them. And Rails

makes it easy for developers to integrate features such as Ajax and RESTful

interfaces into their code, because support is built in. (And if you’re not famil-

iar with Ajax and REST interfaces, never fear—we’ll explain them later in the

book.)

Report erratum

RAILSIS AGILE 18

Developers are worried about deployment too. They found that with Rails you

can deploy successive releases of your application to any number of servers

with a single command (and roll them back equally easily should the release

prove to be somewhat less than perfect).

Rails was extracted from a real-world, commercial application. It turns out

that the best way to create a framework is to ﬁnd the central themes in a

speciﬁc application and then bottle them up in a generic foundation of code.

When you’re developing your Rails application, you’re starting with half of a

really good application already in place.

But there’s something else to Rails—something that’s hard to describe. Some-

how, it just feels right. Of course, you’ll have to take our word for that until

you write some Rails applications for yourself (which should be in the next

forty-ﬁve minutes or so...). That’s what this book is all about.

Rails Is Agile

The title of this book is Agile W e b Development with Rails. Y o u may be sur-

prised to discover that we don’t have explicit sections on applying agile prac-

tices X, Y , and Z to Rails coding.

The reason is both simple and subtle. Agility is part of the fabric of Rails.

Let’s look at the values expressed in the Agile Manifesto as a set of four pref-

erences:

• Individuals and interactions over processes and tools

• W o r k i n g software over comprehensive documentation

• Customer collaboration over contract negotiation

• Responding to change over following a plan

Rails is all about individuals and interactions. There are no heavy toolsets,

no complex conﬁgurations, and no elaborate processes. There are just small

groups of developers, their favorite editors, and chunks of Ruby code. This

leads to transparency; what the developers do is reﬂected immediately in what

the customer sees. It’s an intrinsically interactive process.

Rails doesn’t denounce documentation. Rails makes it trivially easy to cre-

ate HTML documentation for your entire codebase. But the Rails development

process isn’t driven by documents. Y o u won’t ﬁnd 500-page speciﬁcations at

the heart of a Rails project. Instead, you’ll ﬁnd a group of users and devel-

opers jointly exploring their need and the possible ways of answering that

need. Y o u ’ l l ﬁnd solutions that change as both the developers and the users

become more experienced with the problems they’re trying to solve. Y o u ’ l l ﬁnd

1. http://agilemanifesto.org/. Dave Thomas was one of the seventeen authors of this document.

Report erratum

WHOTHISBOOKIS FOR 19

a framework that delivers working software early in the development cycle.

This software may be rough around the edges, but it lets the users start to get

a glimpse of what you’ll be delivering.

In this way, Rails encourages customer collaboration. When customers see

just how quickly a Rails project can respond to change, they start to trust

that the team can deliver what’s required, not just what has been requested.

Confrontations are replaced by “What if?” sessions.

That’s all tied to the idea of being able to respond to change. The strong, almost

obsessive, way that Rails honors the DRY principle means that changes to

Rails applications impact a lot less code than the same changes would in other

frameworks. And since Rails applications are written in Ruby, where concepts

can be expressed accurately and concisely, changes tend to be localized and

easy to write. The deep emphasis on both unit and functional testing, along

with support for test ﬁxtures and stubs during testing, gives developers the

safety net they need when making those changes. W i t h a good set of tests in

place, changes are less nerve-racking.

Rather than constantly trying to tie Rails processes to the agile principles,

we’ve decided to let the framework speak for itself. As you read through the

tutorial chapters, try to imagine yourself developing web applications this way:

working alongside your customers and jointly determining priorities and solu-

tions to problems. Then, as you read the more advanced concepts that follow

in Part III, see how the underlying structure of Rails can enable you to meet

your customers’ needs faster and with less ceremony.

One last point about agility and Rails: although it’s probably unprofessional

to mention this, think how much fun the coding will be.

Who This Book Is For

This book is for programmers looking to build and deploy web-based applica-

tions. This includes application programmers who are new to Rails (and per-

haps even new to Ruby) and ones who are familiar with the basics but want a

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