精通Rails：Agile Web Development with Rails第四版

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"本书《Agile Web Development with Rails》是关于使用Rails框架进行敏捷Web开发的第四版，作者包括Sam Ruby、Dave Thomas和David Heinemeier Hansson。本书适用于Rails 3版本，核心团队持续对Rails进行更新，新版本可能引入与旧版本不兼容的变化。书中提供的示例代码需要安装特定版本的Rails来运行，具体安装步骤可以在第一章找到。通过在命令行输入`rails -v`可以查看当前Rails版本。对于Rails的更新内容及其对本书影响的信息，读者可访问http://www.pragprog.com/wikis/wiki/ChangesToRails。这本书得到了Rails核心贡献者Mikel Lindsaar的高度评价，认为它是新Rails开发者入门的优秀选择。" 本资源主要涉及以下知识点： 1. **Rails框架**: Rails是基于Ruby语言的开源Web应用程序框架，遵循MVC（Model-View-Controller）架构模式，强调“约定优于配置”的开发原则，使得Web应用开发更为简洁高效。 2. **敏捷Web开发**: 敏捷开发是一种迭代和增量的软件开发方法，强调快速响应变化，提高开发效率和软件质量。书中以敏捷开发为核心，教导如何使用Rails实现敏捷Web应用开发。 3. **Rails 3**: 这本书是针对Rails 3版本编写的，该版本引入了许多改进，如ActionMailer和ActiveResource的重大更新，以及对Ruby 1.9的支持等。需要注意的是，不同版本的Rails可能存在代码不兼容的问题。 4. **安装Rails**: 书中的第一章详细介绍了如何安装适合运行书中示例代码的Rails版本，这是开始学习Rails前的基础工作。 5. **版本检查**: 使用`rails -v`命令可以检查当前Rails的版本，这对于确保代码正常运行至关重要，因为不同版本的Rails可能有不同的API和功能。 6. **Rails更新与兼容性**: Rails持续更新，可能会引入新的特性和改变，这些改变可能导致与旧版本的代码不兼容。书中提供了获取有关Rails更新信息的链接，帮助开发者了解这些变化。 7. **开发者资源**: Mikel Lindsaar的推荐强调了本书对于Rails新手的价值，表明它不仅提供了一种全面理解Rails的方式，而且是引导开发者走向成功职业生涯的良好起点。 8. **社区支持**: 通过提及Pragmatic Programmers出版社的wiki，读者可以了解到一个活跃的社区，这个社区会跟踪Rails的变动并提供更新信息，对于持续学习和解决问题非常有帮助。《Agile Web Development with Rails》第四版是一本深入浅出的Rails教程，涵盖了从基础到高级的多个方面，适合初学者和有一定经验的开发者，它强调了敏捷开发的原则，并提供了与Rails框架紧密相关的实践指导。

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

精通Rails：Agile Web Development with Rails第四版

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