使用Rails进行敏捷Web开发

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"Agile Web Development with Rails, 4th Edition 是一本专注于使用 Ruby on Rails 框架进行敏捷Web开发的权威书籍。这本第四版的指南详细讲解了如何利用Rails 3进行高效开发。Rails团队持续更新框架，新版本可能会引入与早期版本不兼容的变动，因此在使用本书时，确保安装的是指定版本的Rails至关重要。" Ruby on Rails，简称Rails，是一个基于Ruby语言的开源Web应用框架，遵循敏捷开发原则，它强调代码的简洁性和开发效率。Rails的核心理念是DRY（Don't Repeat Yourself），鼓励通过元编程和库来减少重复代码。此外，它还采用了MVC（Model-View-Controller）架构模式，使得开发人员可以更清晰地组织应用程序的逻辑。在Rails 3中，开发者可以体验到一系列增强的功能，例如ActionController的改进，使得处理HTTP请求更加灵活；ActiveRecord的升级，提供了更强大的数据库操作和查询API；以及ActiveSupport库的扩展，增加了许多实用的工具和方法。书中会详细阐述这些内容，并引导读者逐步构建实际的Web应用。安装Rails时，按照书中的第1章"Installing Rails"的指导进行，确保使用与书本内容匹配的版本。可以通过在命令行中输入`rails -v`来查看当前安装的Rails版本。若需要更新或安装特定版本，可以使用Ruby的包管理器Bundler进行管理。随着Rails框架的不断更新，开发者需要时刻关注官方的变更信息，以便及时适应新特性或调整代码以保持兼容性。Rails社区通常会提供详细的迁移指南，帮助现有应用顺利过渡到新版本。本书中提到，关于影响本书内容的Rails更新信息，可以在http://web.archive.org/web/2017020.jpg的链接（原链接已失效，可能需查找替代资源）上找到。学习Rails不仅可以掌握一个强大的Web开发工具，还能深入了解敏捷开发理念和最佳实践。本书通过丰富的示例和详细的解释，帮助开发者快速掌握Ruby on Rails，从而提升开发效率和创建高质量的Web应用程序。同时，LinuxIDC.com作为提供Linux相关信息和技术支持的平台，也是学习者获取最新IT资讯、Linux发行版技术资料和社区交流的好去处。

ACKNOWLEDGMENTS 15

Finally, the Rails core team has been incredibly helpful, answering questions,

checking out code fragments, and ﬁxing bugs. A big “thank you” to the follow-

ing:

Scott Barron (htonl), Jamis Buck (minam), Thomas Fuchs (madrobby),

Jeremy Kemper (bitsweat), Y e h u d a Katz (wycats),

Michael Koziarski (nzkoz), Marcel Molina Jr, (noradio),

Rick Olson (technoweenie), Nicholas Seckar (Ulysses),

Sam Stephenson (sam), Tobias Lütke (xal), José V a l i m (josevalim), and

Florian W e b e r (csshsh)

Sam Ruby

March 2011

rubys@intertwingly.net

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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.)

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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.

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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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