Rails 3 开发指南：Agile Web Development with Rails (第4版)

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"本书专注于Rails 3版本的Web开发，并且提醒读者，Rails核心团队持续更新Rails，可能会引入与早期版本不兼容的变化。为了运行书中的示例，必须按照第1章‘安装Rails’（第24页）的说明安装正确的Rails版本。通过在命令行输入'rake -v'可以查询当前Rails的版本。如需了解影响本书内容的Rails变更，可访问http://www.pragprog.com/wikis/wiki/ChangesToRails获取信息。" 在深入探讨Agile Web Development with Rails这本书的内容之前，我们首先需要理解关于Rails版本的重要性。Rails是一个快速发展的开源Web应用程序框架，由Ruby编程语言编写。书中强调，由于Rails的持续更新，新版本可能不兼容旧版本的代码，因此对于学习者来说，确保使用与书籍匹配的Rails版本至关重要。这不仅影响到代码的执行，还可能影响到对书中概念的理解。安装正确的Rails版本是开始学习的基础。在第1章“安装Rails”中，作者会详细介绍如何安装和配置适合本书的Rails环境。这对于初学者来说是非常关键的步骤，因为正确的环境设置能够确保他们能顺利地运行书中的示例代码，从而更好地理解和掌握Rails的工作原理。此外，书中的一个重要工具是通过命令行运行'rake -v'来检查当前Rails的版本。这是一个实用技巧，开发者在日常工作中也会频繁用到，以便随时了解自己的开发环境是否与项目需求或最新的Rails版本保持一致。 Rails的更新通常伴随着功能增强、性能优化和问题修复。对于开发者来说，关注Rails的变更信息是保持技术更新和提高生产力的关键。书中提到的网站http://www.pragprog.com/wikis/wiki/ChangesToRails提供了这些信息，帮助读者了解哪些变动可能影响到书中内容，以便进行相应的调整。书评人Mikel Lindsaar，作为Rails核心贡献团队的一员，肯定了这本书对新开发者的价值，指出它提供的全面视角有助于初学者迅速融入Rails社区并建立成功的职业生涯。最新版继续保持这一传统，仍然是他向新Rails开发者首推的读物。 Agile Web Development with Rails 4th版是一本面向Rails 3的权威指南，强调版本匹配的重要性，提供详细的安装指导，帮助开发者紧跟Rails的发展步伐。书中的实践示例和对Rails框架的深入讲解，使得它成为Rails学习者的宝贵资源。

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

Rails 3 开发指南：Agile Web Development with Rails (第4版)

(应用Rails进行敏捷Web开发(第4版) Agile.Web.Development.with.Rails.4th.Edition 原版

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