Rails 2.2.2 敏捷Web开发实战

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"《敏捷网页开发 with Rails》第三版，由 Sam Ruby、Dave Thomas 和 David Heinemeier Hansson 合著，与 Leon Breedt、Mike Clark、James Duncan Davidson、Justin Gehtland 及 Andreas Schwarz 共同编写。本书是关于使用 Rails 2.2.2 版本进行敏捷网页开发的指南。" 在敏捷开发领域，《敏捷网页开发 with Rails》是一本极具影响力的书籍。它专注于使用 Ruby on Rails 框架进行高效的 Web 应用程序开发。Rails 是一个开源的 MVC（模型-视图-控制器）框架，它以其生产力高、开发速度快而闻名。此书的第三版，重点关注 Rails 2.2.2 版本，但随着 Rails 的持续更新，可能会出现与新版本不兼容的情况。作者们特别提醒读者，Rails 核心团队不断在开发新版本，这可能导致新版本对基于旧版 Rails 编写的代码产生不兼容性。Sam Ruby 在 Pragmatic Programmers 的 wiki 上维护了一个页面，记录了 Rails 更新对本书内容可能产生的影响（http://www.pragprog.com/wikis/wiki/ChangesToRails），对于正在使用 Rails 新版本的开发者来说，这是一个宝贵的资源。为了确定当前运行的 Rails 版本，可以使用命令行工具输入 `rails -v` 命令。这个简单的操作有助于开发者了解自己的环境是否与书中代码兼容。这本书详细介绍了 Rails 开发的各个方面，包括模型（Model）的创建和数据操作、视图（View）的布局与设计，以及控制器（Controller）如何协调两者。此外，还涵盖了测试驱动开发（TDD）、集成测试、部署策略、数据库交互、RESTful 设计原则等关键概念。通过学习《敏捷网页开发 with Rails》，开发者不仅可以掌握 Rails 框架的基本用法，还能深入了解敏捷开发的方法论，提升开发效率，实现快速迭代和高质量的软件交付。书中的实例和实践指导将帮助读者快速上手并精通 Rails 开发，以适应快速变化的 Web 开发需求。

RAILS IS AGILE 16

it easy for d evelopers to integrate featur es su ch as Ajax and RESTful interfaces

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 successive releases of your app lication to any number of servers

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

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 t o 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 R ails—something that’s hard to describe. Some-

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

you wr ite some Rails applications for yourself (which should b e in the next 45

minutes or so...). Tha t ’s what this book is all about.

1.1 Rails Is Agile

The title of this book is Agile Web Development with Rails. You may be sur-

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

tices X, Y, and Z to Rails coding.

The reason is both simple and subtle. Agili ty 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 favor s the followi ng:

• Individuals and interactions over processes and tools

• Working softw are over comprehensive documentation

• Customer collaborati on over contract negotiation

• Responding to change over following a plan

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

no complex conﬁgurati ons, 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 intrinsica lly interactive process.

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

ate HTML documentation for you r entire codebase. But the Rails development

process isn’t driven by documents. You won’t ﬁnd 500-page speciﬁcations a t

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

opers jointly exploring their need and the possible wa ys of answering that

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

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

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

This software may be rough around the edges, but it l et s 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 appl ications are written in Ruby, where concepts

can be expressed accurately and concisely, changes tend to be locali zed and

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

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

safety net they need when ma king those changes. With a good set of tests in

place, changes are less nerve-r acking.

Rather than constantly trying to tie Rails processes to the agile princip les,

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

tutorial chapters, try t o imagine yourself devel oping web applications this way:

working alongside your customers and jointly determining priorities and solu-

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

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

tomers’ needs faster and wit h 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.

1.2 Finding Your Way Around

The ﬁrst two p arts of this b ook are an i ntroduction to the concepts behind

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

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

folks seem to enjoy bu ilding the applica tion along with the book. If you don’t

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

compressed tar archive or a zip ﬁl e).

2. http://www.pragprog.com/titles/rails3/code.html has the link s for the downloads.

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FINDING YOUR WAY AROUND 18

The third part of the book, starting 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 y our Rails applications

efﬁciently 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 downl oad. To help you ﬁnd your way, if a code listing

can be found in the download, there’ll be a bar above the snippet (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 browser wind ow.

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 exi sting ﬁl e where the

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

some helpful little triangles on the left of the lines that you will need to

change. T wo such lines are indicated in the previou s code.

Ruby Tips

Although you need to know Ruby to write Rails applications, we rea lize

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

at the same time. Appendix

A, on page 666, is a (very) brief introduction

to the Ruby language. When we use a Ruby-speciﬁc construct for the

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

paragraph contains a g ratuitous use of

:name, a Ruby sy mbol. 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 b ook....

David Says...

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

where David Heinemeier Hansson gives you 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 Ra ils pr o.

Joe Asks...

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

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

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

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

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

that documentation whenever you install Rails, and it’s g uaranteed 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 API s by pointing your

browser at

http://localhost:8808.

Rails Ver sions

This book is based on Rails 2.0. In particular, its code has been run ag ainst

the Rails 2.2.2 RubyGem.

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

than likely that future versions will, too.

1.3 Acknowledgments

You’d think that produci ng a third edition of a book would be easy. After all,

you already have all the text. It’s just a tweak to some code here and a minor

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

It’s difﬁ cult to tell exactly, but our impression is that cr eating ea ch 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 addition of the deprecation mecha-

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

lukewarm.

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

Ruby and Rails communities. As with the original, this book wa s rel eased as

a beta book: early versions 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 incorporated, making thi s book

immeasurably more useful than it would have been. Thank you a ll, both for

supporting the beta book program and for contributing so much valuab le

feedback.

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