Rails 2.2.2 敏捷Web开发指南

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"Agile Web Development with Rails" 本书《Agile Web Development with Rails》是针对Rails框架的敏捷Web开发指南，特别关注Rails 2.2.2版本。Rails是由Ruby编程语言构建的一个开源Web应用程序框架，它提倡敏捷开发方法，强调简洁、生产力和乐趣。在编写这本书时，作者已对所有代码进行了详尽的测试，确保与Rails 2.2.2版本兼容。 Rails的核心团队持续更新和改进框架，因此在本书出版后，可能会有新的Rails版本发布，这些新版本可能引入与旧版Rails不兼容的变化，包括书中提供的代码。Sam Ruby负责在项目wiki（http://pragprog.wikidot.com/changes-to-rails）上跟踪这些影响本书内容的Rails变更。如果你正在使用比Rails 2.2.2更晚的版本，建议查阅这个wiki页面，了解是否需要对书中的代码进行调整。要检查当前系统中安装的Rails版本，可以在命令行中运行`rails -v`命令。该书由Sam Ruby、Dave Thomas和David Heinemeier Hansson共同撰写，并有其他多位专家参与，如Leon Breedt、Mike Clark、James Duncan Davidson、Justin Gehtland和Andreas Schwarz。它是The Pragmatic Bookshelf系列的一部分，出版社位于北卡罗来纳州的罗利和德克萨斯州的达拉斯。值得注意的是，书中提到的制造商和销售商用来区分其产品的许多名称可能是注册商标。这表明作者们尊重并认识到软件行业中商标的重要性，同时提醒读者在实际应用中需要考虑知识产权问题。在学习本书时，读者将深入理解如何利用Rails的敏捷开发理念来构建高效、可扩展的Web应用。内容可能涵盖MVC架构、路由、数据库交互（ActiveRecord）、测试驱动开发（TDD）、敏捷开发实践以及与Rails生态系统相关的各种工具和技术。通过本书，开发者不仅可以提升技能，还能了解到如何适应和应对Rails框架的不断变化，保持代码的最新性和适应性。

RAILS IS AGILE 16

it easy for devel opers to integrate features such as Ajax and RESTful inter faces

into their code, because support is built in. (And if you’re not familiar with Ajax

and REST interfaces, never fear—we’ll explain them later in the book.)

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

can depl oy successi ve releases of your applica tion to any number of servers

with a single command (and roll them back equa lly 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 cr eate 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 applica tion, you’re starting with half of a

reall y good application alrea d y in place.

But there’s something el se 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 45

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

1.1 Rails Is Agile

The title of this book is A

gile Web Development with Rails. You 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:

Agile development favors the following:

•

Individuals and interactions over processes and tools

• Working 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 i s reﬂected immedia tely 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. You won’t ﬁnd 50 0 -page speciﬁcations at

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

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FINDING YOUR WAY AROUND 17

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

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

need. You’ll ﬁnd solutions that change as both the developers and the users

become more experienced with the p roblems they’re trying to solve. You’ll ﬁnd

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

This software ma y be rough around the edges, but it lets the users sta rt to get

a glimpse of what you’ll be delivering.

In this way, Rails encoura ges cu stomer 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, w ay 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 accura tely and concisely, changes tend to be localized and

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

with support for test ﬁxtures and stu b s during testing, gives developers the

safety net they need when mak ing those changes. With a g ood set of tests in

place, changes are less nerve-racking.

Rather than constantl y trying to tie Rails processes to the agile principles,

we’ve decid ed to let the fr amework speak for itself. As you read through the

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

working alongside your customers and jointly determining priorities and solu-

tions to problems. Then, a s you read the deeper reference material in the back,

see how the underlying structure of Rails can enable you to meet you r cus-

tomers’ needs faster and with less ceremony.

One last point abou t agility and Rails: although it’s probably unprofessional

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

1.2 Finding Your Way Around

The ﬁrst two parts of this book are an i ntroduction to the conce

pts behind

Rails and an extended example—we b uild a simple online store. This is the

place to start if you’re looking to get a feel for Rails pr ogramming. In fact, most

folks seem to enjoy building the appli cation along with the book. If y ou don’t

want to do all that typing, you can cheat and download the source code ( a

compressed tar archive or a zip ﬁle).

2. http://www.pragprog.c om/titles/rails3/code.html has the links for the downloads.

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FINDING YOUR WAY AROUND 18

The third part of the book, starti ng on page 257, is a detailed look at all the

functions and facilities of Rails. This is where you’ll go to ﬁnd out how to

use the various Rails components and how to deploy your R ails applications

efﬁci ently and safely.

Along the way, you’ll see various conventions we’ve adopted.

Live Code

Most of the code snippets we show come from full-length, running exam-

ples that you can download . To help y ou ﬁnd your way, if a code listing

can be found in the d ownload, there’ll be a bar above the sni p p et (just

like the one here).

Download work/demo1/app/controller s/say_controller.rb

class SayController < ApplicationController

def hello

end

This contains the path to the code within the download. If you’

re reading

the PDF version of this book and your PDF viewer supports hyperlinks,

you can click the bar, and the code should appear in a brow ser window.

Some browsers (such as Safari) will mistakenly try to interpret some of

the templates as HTML. If this happens, view the source of the page to

see the real source code.

And in some cases involving the modiﬁcation of an existing ﬁle where the

lines to be changed may not be immediately obvious, you will also see

some helpfu l little triangles on the l eft of the lines that you will need to

change. Two such lines are indicated in the previous code.

Ruby Tips

Although you need to know Ruby to write Ra ils applications, we realize

that many folks reading this book will be learning both Ruby and Rails

at the same time. Appendix A , on page 666, is a (very) brief introduction

o the Ruby language. When we use a Ruby-speciﬁc constr uct for the

ﬁrst time, we’ll cr oss-reference it to that appendix. For example, this

paragraph contains a gratuitous use of :name, a Ruby symbol. In the :

name

֒→ page

668

margin, you’ll see an indication that symbols are explained on page 668.

So, if you don’t know Ruby or if you need a quick refresher, you might

want to read Appendix A, on page 666, before you go too much further.

There’s a lot of code in this book....

David Says.. .

Every now and then you’ll come across a David Says... sidebar. Here’s

where David Heinemeier Hansson gi ves y ou the real scoop on some par-

ticular aspect of Rails—rationales, tricks, recommendations, and more.

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ACKNOWLEDGMENTS 19

Because he’s the fellow who invented Rails, these are the sections to read

if you want to become a Rails pro.

Joe As ks ...

Joe, the mythical developer, sometimes pops up to ask questions about

stuf f we talk about in the text. We answer these questions as we go along.

This book isn’t a reference manual for Rails. We show most of the modules and

most of their methods, either by example or narratively in the text, but we don’t

have hundreds of pages of API listings. There’s a good reason for this—you get

that documentation whenever you install Rails, and it’s guaranteed to be more

up-to-date than the material in this book. If you install Rails using RubyGems

(which we recommend), simply start the gem documentation server ( using the

command gem server), and you can access all the Rails APIs by pointing your

rowser at

http://localhost:8808.

Rails Versions

This book is based on Rails 2.0. In parti cular, its code has been run against

the Rails 2.2.2 RubyGem.

Previous versions of R ails contain incompatibilities with 2.2.2, and it is more

than likely that future versions will, too.

1.3 Acknowledgments

You’d think that producing a third edition of a book would be ea

sy. After all,

you already have all the text. I t’s just a twea k to some code here and a minor

wording change there, and you’re done. You’d think....

It’s difﬁcult to tell exactly, but our impression is that creating each edition of

Agile Web Development with Rails took about as much effort as the ﬁrst edi-

tion. Rails is constantly evolving and, as it does, so has this book. Parts of the

Depot application were rewritten several times, and all of the narrative was

updated. The emphasis on REST and the addi tion of the deprecation mecha-

nism all changed the structure of the book as what was once hot became just

lukewarm.

So, this book would not exist without a massive amount of help from the

Ruby and Rai ls communities. As with the original, this book was released as

a beta book: early versi ons were posted as P DFs, and people made comments

online. A nd comment they did: more than 1,200 suggestions and bug reports

were posted. The vast majority ended up being incorpor ated, making this book

immeasurably more useful than it would have been. T hank you all, both for

supporting the beta book program and for contribu ting so much valuable

feedback.

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