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Beta
Book
Agile publishing for agile developers
Under Construction The book you’re reading is still under development. As
part of our Beta book program, we’re releasing this copy well before a normal
book would be released. That way you’re able to get this content a couple of
months before it’s available in finished form, and we’ll get feedback to make
the book even better. The idea is that everyone wins!
Be warned. The book has not had a full technical edit, so it will contain
errors. It has not been copyedited, so it will be full of typos and other weirdness. And there’s been no effort spent doing layout, so you’ll find bad page
breaks, over-long lines with little black rectangles, incorrect hyphenations,
and all the other ugly things that you wouldn’t expect to see in a finished
book. We can’t be held liable if you use this book to try to create a spiffy
application and you somehow end up with a strangely shaped farm implement instead. Despite all this, we think you’ll enjoy it!
Download Updates Throughout this process you’ll be able to download
updated ebooks from your account on http://pragprog.com. When the book
is finally ready, you’ll get the final version (and subsequent updates) from the
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Send us your feedback In the meantime, we’d appreciate you sending us
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the links at the bottom of each page.
Thank you for being part of the Pragmatic community!
Andy & Dave
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Agile Web Development with Rails
Fourth Edition
Sam Ruby
Dave Thomas
David Heinemeier Hansson
with Leon Breedt
Mike Clark
James Duncan Davidson
Justin Gehtland
Andreas Schwarz
The Pragmatic Bookshelf
Raleigh, North Carolina Dallas, Texas
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Many of the designations used by manufacturers and sellers to distinguish their products are
claimed as trademarks. Where those designations appear in this book, and The Pragmatic Programmers, LLC was aware of a trademark claim, the designations have been printed in initial capital
letters or in all capitals. The Pragmatic Starter Kit, The Pragmatic Programmer, Pragmatic Programming, Pragmatic Bookshelf and the linking g device are trademarks of The Pragmatic Programmers,
LLC.
Every precaution was taken in the preparation of this book. However, the publisher assumes no
responsibility for errors or omissions, or for damages that may result from the use of information
(including program listings) contained herein.
Our Pragmatic courses, workshops, and other products can help you and your team create better
software and have more fun. For more information, as well as the latest Pragmatic titles, please
visit us at http://www.pragprog.com.
Copyright © 2010 The Pragmatic Programmers LLC.
All rights reserved.
No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any
form, or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the
prior consent of the publisher.
Printed in the United States of America.
ISBN-10: 1-934356-54-9
ISBN-13: 978-1-934356-54-8
Printed on acid-free paper.
B11.0 printing, November 24, 2010
Version: 2010-11-24
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Contents
Changes in the Beta Releases 10
Beta 11—November 24 . . . . . . . . . . . . . . . . . . . . . . . . . 10
Beta 10—October 28 . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Beta 9—October 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Beta 8—September 9 . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Beta 7—August 25 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Beta 6—July 27 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Beta 5—June 28 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Beta 4—May 26 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Beta 3—May 11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Beta 2—May 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Preface to the Fourth Edition 15
Acknowledgements 17
Introduction 19
Rails Simply Feels Right . . . . . . . . . . . . . . . . . . . . . . . . . 19
Rails Is Agile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Who This Book Is For . . . . . . . . . . . . . . . . . . . . . . . . . . 22
How To Read This Book . . . . . . . . . . . . . . . . . . . . . . . . . 22
Part I—Getting Started 26
1 Installing Rails 27
1.1 Installing on Windows . . . . . . . . . . . . . . . . . . . . . . 27
1.2 Installing on Mac OS X . . . . . . . . . . . . . . . . . . . . . 29
1.3 Installing on Linux . . . . . . . . . . . . . . . . . . . . . . . . 30
1.4 Choosing a Rails Version . . . . . . . . . . . . . . . . . . . . 31
1.5 Setting Up Your Development Environment . . . . . . . . . 32
1.6 Rails and Databases . . . . . . . . . . . . . . . . . . . . . . . 36
1.7 What We Just Did . . . . . . . . . . . . . . . . . . . . . . . . 37
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CONTENTS 6
2 Instant Gratification 38
2.1 Creating a New Application . . . . . . . . . . . . . . . . . . . 38
2.2 Hello, Rails! . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
2.3 Linking Pages Together . . . . . . . . . . . . . . . . . . . . . 47
2.4 What We Just Did . . . . . . . . . . . . . . . . . . . . . . . . 49
3 The Architecture of Rails Applications 51
3.1 Models, Views, and Controllers . . . . . . . . . . . . . . . . 51
3.2 Rails Model Support . . . . . . . . . . . . . . . . . . . . . . . 54
3.3 Action Pack: The View and Controller . . . . . . . . . . . . 56
4 Introduction to Ruby 58
4.1 Ruby Is an Object-Oriented Language . . . . . . . . . . . . 58
4.2 Data Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
4.3 Logic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.4 Organizing Structures . . . . . . . . . . . . . . . . . . . . . . 66
4.5 Marshaling Objects . . . . . . . . . . . . . . . . . . . . . . . 69
4.6 Pulling It All Together . . . . . . . . . . . . . . . . . . . . . . 69
4.7 Ruby Idioms . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Part II—Building an Application 73
5 The Depot Application 74
5.1 Incremental Development . . . . . . . . . . . . . . . . . . . . 74
5.2 What Depot Does . . . . . . . . . . . . . . . . . . . . . . . . . 75
5.3 Let’s Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
6 Task A: Creating the Application 81
6.1 Iteration A1: Creating the Products Maintenance Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
6.2 Iteration A2: Making Prettier Listings . . . . . . . . . . . . . 88
7 Task B: Validation and Unit Testing 95
7.1 Iteration B1: Validating! . . . . . . . . . . . . . . . . . . . . . 95
7.2 Iteration B2: Unit Testing of Models . . . . . . . . . . . . . 100
8 Task C: Catalog Display 109
8.1 Iteration C1: Creating the Catalog Listing . . . . . . . . . . 109
8.2 Iteration C2: Adding a Page Layout . . . . . . . . . . . . . . 112
8.3 Iteration C3: Using a Helper to Format the Price . . . . . . 116
8.4 Iteration C4: Functional Testing of Controllers . . . . . . . 116
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CONTENTS 7
9 Task D: Cart Creation 121
9.1 Iteration D1: Finding a Cart . . . . . . . . . . . . . . . . . . 121
9.2 Iteration D2: Connecting Products to Carts . . . . . . . . . 122
9.3 Iteration D3: Adding a Button . . . . . . . . . . . . . . . . . 124
10 Task E: A Smarter Cart 130
10.1 Iteration E1: Creating a Smarter Cart . . . . . . . . . . . . 130
10.2 Iteration E2: Handling Errors . . . . . . . . . . . . . . . . . 134
10.3 Iteration E3: Finishing the Cart . . . . . . . . . . . . . . . . 138
11 Task F: Add a Dash of Ajax 143
11.1 Iteration F1: Moving the Cart . . . . . . . . . . . . . . . . . 144
11.2 Iteration F2: Creating an Ajax-Based Cart . . . . . . . . . . 149
11.3 Iteration F3: Highlighting Changes . . . . . . . . . . . . . . 152
11.4 Iteration F4: Hiding an Empty Cart . . . . . . . . . . . . . . 154
11.5 Testing Ajax changes . . . . . . . . . . . . . . . . . . . . . . 158
12 Task G: Check Out! 163
12.1 Iteration G1: Capturing an Order . . . . . . . . . . . . . . . 163
12.2 Iteration G2: Atom Feeds . . . . . . . . . . . . . . . . . . . . 177
12.3 Iteration G3: Pagination . . . . . . . . . . . . . . . . . . . . . 181
13 Task H: Sending Mail 186
13.1 Iteration H1: Sending Confirmation E-mails . . . . . . . . . 186
13.2 Iteration H2: Integration Testing of Applications . . . . . . 193
14 Task I: Logging In 199
14.1 Iteration I1: Adding Users . . . . . . . . . . . . . . . . . . . 199
14.2 Iteration I2: Authenticating Users . . . . . . . . . . . . . . . 208
14.3 Iteration I3: Limiting Access . . . . . . . . . . . . . . . . . . 213
14.4 Iteration I4: Adding a Sidebar, More Administration . . . . 216
15 Task J: Internationalization 221
15.1 Iteration J1: Selecting the locale . . . . . . . . . . . . . . . . 222
15.2 Iteration J2: Translating the Store Front . . . . . . . . . . . 224
15.3 Iteration J3: Translating Checkout . . . . . . . . . . . . . . 231
15.4 Iteration J4: Add a Locale Switcher . . . . . . . . . . . . . . 237
16 Task K: Deployment and Production 241
16.1 Iteration K1: Deploying with Phusion Passenger and MySQL 243
16.2 Iteration K2: Deploying Remotely with Capistrano . . . . . 248
16.3 Iteration K3: Checking Up on a Deployed Application . . . 254
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CONTENTS 8
17 Depot Retrospective 258
17.1 Rails Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . 258
17.2 Documenting What We Have Done . . . . . . . . . . . . . . 261
Part III—Rails In Depth 263
18 Finding Your Way Around Rails 264
18.1 Where things go . . . . . . . . . . . . . . . . . . . . . . . . . 264
18.2 Naming Conventions . . . . . . . . . . . . . . . . . . . . . . 273
19 Active Record 277
19.1 Defining your Data . . . . . . . . . . . . . . . . . . . . . . . . 277
19.2 Locating and Traversing Records . . . . . . . . . . . . . . . 282
19.3 Creating, Reading, Updating, and Deleting (CRUD) . . . . 285
19.4 Participating in the Monitoring Process . . . . . . . . . . . 301
19.5 Transactions . . . . . . . . . . . . . . . . . . . . . . . . . . . 308
20 Action Dispatch and Action Controller 313
20.1 Dispatching Requests to Controllers . . . . . . . . . . . . . 313
20.2 Processing of Requests . . . . . . . . . . . . . . . . . . . . . 324
20.3 Objects and operations that span requests . . . . . . . . . 335
21 Action View 345
21.1 Using Templates . . . . . . . . . . . . . . . . . . . . . . . . . 345
21.2 Generating Forms . . . . . . . . . . . . . . . . . . . . . . . . 347
21.3 Processing Forms . . . . . . . . . . . . . . . . . . . . . . . . 350
21.4 Uploading Files to Rails Applications . . . . . . . . . . . . . 352
21.5 Using Helpers . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
21.6 Reducing Maintenance with Layouts and Partials . . . . . 362
22 Caching 371
22.1 Page Caching . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
22.2 Expiring Pages . . . . . . . . . . . . . . . . . . . . . . . . . . 374
22.3 Fragment Caching . . . . . . . . . . . . . . . . . . . . . . . . 380
23 Migrations 386
23.1 Creating and Running Migrations . . . . . . . . . . . . . . . 386
23.2 Anatomy of a Migration . . . . . . . . . . . . . . . . . . . . . 389
23.3 Managing Tables . . . . . . . . . . . . . . . . . . . . . . . . . 393
23.4 Advanced Migrations . . . . . . . . . . . . . . . . . . . . . . 397
23.5 When Migrations Go Bad . . . . . . . . . . . . . . . . . . . . 401
23.6 Schema Manipulation Outside Migrations . . . . . . . . . . 402
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CONTENTS 9
24 Non-Browser Applications 404
24.1 A Standalone Application Using Active Record . . . . . . . 404
24.2 A Library Function Using Active Support . . . . . . . . . . 405
24.3 A Remote Application Using Active Resource . . . . . . . . 410
25 Rails’ Dependencies 416
25.1 Generating XML with Builder . . . . . . . . . . . . . . . . . 416
25.2 Generating HTML with ERb . . . . . . . . . . . . . . . . . . 418
25.3 Managing Dependencies with Bundler . . . . . . . . . . . . 420
25.4 Interfacing with the web server with Rack . . . . . . . . . . 422
25.5 Automating Tasks with Rake . . . . . . . . . . . . . . . . . . 426
25.6 Survey of Rails’ Dependencies . . . . . . . . . . . . . . . . . 427
26 Rails Plugins 431
26.1 Credit Card Processing with Active Merchant . . . . . . . . 431
26.2 Saving Bandwidth with Asset Packager . . . . . . . . . . . 433
26.3 Beautifying our Markup with Haml . . . . . . . . . . . . . . 435
26.4 Write Less and Do More with JQuery . . . . . . . . . . . . . 438
26.5 Finding more at RailsPlugins.org . . . . . . . . . . . . . . . 440
27 Where to Go From Here 443
A Bibliography 445
Index 446
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Changes in the Beta Releases
Beta 11—November 24
This beta incorporates a substantial amount of feedback from a number of
sources including errata, formal reviews, and from the wonderful editor of
this book. For the first time since putting this book out in beta, I am going
to suggest that if you are well under way with Depot using a previous beta,
consider keeping on with that beta. While there has been no major changes,
there have been enough minor changes that those that wish to use this book
are encouraged to start over.
This draft has also been tested against the Rails 3.0.3 release. No changes
were needed to make the code in this book work against that release.
As always, thanks for all of the wonderful feedback via the errata, forums, and
other venues. At this time I would like to specifically thank Johnathan Ritzi,
David Kapp, and Jason Holloway. If you spot something, it is not too late to
make a comment: there will be at least one more errata sweep before final
printing.
Beta 10—October 28
This beta introduces a chapter on plugins and completes the first draft. Plugins are not merely an afterthought or an advanced feature of Rails, with Rails
3.0 it is a fully architected way to augment or even replace base Rails functionality.
This also completes the first draft. If you spot something missing, now would
be an excellent time to report it via the forums or via an errata. After a few
weeks of addressing comments it will be onto production where formatting
and typographical and indexing glitches will be resolved.
This draft has also been tested against the Rails 3.0.1 release. No changes
were needed to make the code in this book work against that release.
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BETA 9—OCTOBER 6 11
Beta 9—October 6
With this beta comes a new chapter on Rails’ dependencies. Understanding
these dependencies are as important as understanding Rails itself. Introducing
this chapter has produced a minor shifting of content: some text that originally
was present in the rather large chapter on Action View has moved into this one.
Additional shifts are expected in the next beta: all such will be noted here.
While running with edge rails directly from git is not recommended at this
time, those that do run such may spot that csrf_meta_tag has been renamed to
csrf_meta_tags in that release. This does not affect any scenario in the book.
As always, thanks for all of the wonderful feedback via the errata, forums, and
other venues. At this time I would like to specifically thank Leonel S, Martin
Zoller, and Jim Puls.
Beta 8—September 9
Rails 3.0 final has shipped! Even better news: no API changes that affect the
book were introduced in the process. In one case, namely in the use of an
Action View helper from a standalone library, you will want to be using the
final release instead of any previous beta or release candidate, so please do
upgrade now if you haven’t already.
New with this beta are three new chapters completing the coverage of the
externals of Rails. Caching covers how to effectively optimize your application by eliminating the overhead of re-computing results that rarely change.
Migrations covers how to maintain your schemas. And finally, Non-Browser
Applications shows you how to access some or all of Rails functions either
locally or remotely.
As we enter into the home stretch, your feedback becomes all the more important. There is an Report Erratum link at the bottom right of every page. Use it
when you spot something, even if you aren’t sure! If you would like to start a
discussion, the forum is a better place for that.
Beta 7—August 25
We have a new release candidate of Rails, as well as an official release of Ruby
1.9.2. I’m pleased to report that once again, no changes were made to any Rails
API that affect the book. Furthermore, the regression that in the first release
candidate which broke the ability to build the guides has been addressed.
New with this beta is a chapter on Action View, which covers templates, helpers,
layouts, and partials. At this point, all three parts of the Model/View/Controller
architecture are covered. Next up will be a chapter on accessing Rails applications from outside of a web server, either directly via APIs or as a web service.
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BETA 6—JULY 27 12
As always, thanks for all of the wonderful feedback via the errata, forums, and
other venues. At this time I would like to specifically thank Kim Shrier, Don
Smith, mltsy, and Jason Catena.
Beta 6—July 27
The big news is that the release candidate for Rails has officially shipped. The
better news is that no API changes were made to Rails that affect the book.
Hopefully at this point releases of Rails will be made more quickly, and the API
will remain stable.
New with this beta is a chapter on Action Dispatch and Action Controller,
which covers both dispatching of requests to controllers, as well as controllers
themselves. At this point, two of the three parts on the Model/View/Controller
architecture are complete. Next up will be a chapter on Views.
Once again, thanks for all of the wonderful feedback via the errata, forums,
and other venues – keep it coming!
Beta 5—June 28
As I write this, the release candidate which was originally due on June 8th has
still not shipped, and we have decided to release a beta anyway. At the current
time, the contents of the book work with beta 4 and with the latest version of
Rails from github, but things could change between now and when the release
candidate ships.
The changes to Rails that affected this book in beta 4 were the requirement
to specify the keyword ’new’ when creating a new application with the ’rails’
command, and the fact that Rails 3.0 no longer works on Ruby 1.9.1. Ruby
1.9.2 preview 3, however, has come out and Rails 3.0 works just fine on it.
This beta has been updated to reflect these changes.
This beta also adds a chapter dedicated to Active Record, a topic which covered
three chapters in edition 3. The content has been updated to reflect Rails 3
APIs, and in particular ARel functionality. The content has been streamlined
to focus only on APIs that everybody needs to know, as well as content that
was adequately covered in Part II. It also reads less like a reference manual,
and more like a guide. Feedback welcome. In particular, please let me know if
something you feel is essential was not covered.
Again, thanks for all of the excellent errata. At this point, we are up to over
300 errata comments from over 80 individuals. I’d like to specifically thank
Seth Arnold, David Hadley, Will Bowlin, Victor Marius Costan, Kristian Riiber
Mandrup, Joe Straitiff, and Andy Brice.
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BETA 4—MAY 26 13
Beta 4—May 26
This beta adds two chapters. The first recaps what was learned in part 2:
model, view, controller, configuration, testing, and deployment. It then continues with an explanation on how to generate documentation for your application.
Chapter 18 is also new with this beta: it goes directory by directory through
your Rails application, describing what goes into each. You will see how to
generate documentation for Rails itself, how to build a Rake task, more information on configuration options and naming conventions. This all sets the
stage for the chapters that follow.
The Rails team is in the process of deprecating config.log_path, but at the
present time has not settled on its replacement. Furthermore this property
is broken in Rails 3 beta 3. What you see in Section 16.3, Dealing with Log
Files, on page 255 reflects what currently works, which may not necessarily
be what will be supported in the final release.
Beta 3—May 11
This beta adds a deployment chapter which takes you through the installation,
configuration, and usage of a number of tools: Apache, Capistrano, MySQL,
and Passenger; as well as (mildly) deeper usage of Git and Bundler.
There’s not been another beta of Rails yet, so this is just a FYI at this point,
but usage of {{name}} syntax in i18n strings will be deprecated; the preferred
syntax is now %{name}.
As always thanks for all of the wonderful feedback via the errata, forums, and
other venues – keep it coming!
Beta 2—May 3
Thanks for all of the excellent feedback. To date we’ve gotten over 100 comments from over 30 individuals. Special thanks go out to Trung LE, David
Hadley, Manuel E Vidaurre Arenas, Wayne Conrad, and Steve Nicholson. A lot
of the changes you’ll see in this second beta are the result of this input. Please
keep it up, as every comment helps us make this book better!
This new release adds coverage of sending mail and integration testing in the
new chapter “Task H: Sending Mail.” You’ll learn how to send mail, how to
function test mail, and how to integration test an end-to-end scenario spanning adding a product to a cart to the sending of a confirmation email.
Only one change to Rails affects the book this go around: Rails will be changing
the way that I18N and HTML safe strings interact. The text in the book has
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BETA 2—MAY 3 14
been partially updated to reflect the new direction, but will continue to work
with Beta 3.
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Preface to the Fourth Edition
When Dave asked me to join as a coauthor of the third edition of this book,
I was thrilled. After all, it was from the first printing of the first edition of
this book that I had learned Rails. Dave and I also have much in common.
Although he prefers Emacs and Mac OS X and my preferences tend toward Vim
and Ubuntu, we both share a love for the command line and getting our fingers dirty with code—starting with tangible examples before diving into heavy
theory.
Since the time the third edition was published (and, in fact, since the first, second and third editions), much has changed. Rails is in the process of being significantly refactored, mostly internally. A number of features that were used in
previous examples have been initially deprecated and subsequently removed.
New features have been added, and much experience has been obtained as to
what the best practices are for using Rails. Rails now also works on Ruby 1.9,
and each of the examples have been tested with Ruby 1.8.7 and Ruby 1.9.2.
Additionally, Rails has exploded from being a popular framework to an active
and vibrant ecosystem, complete with many popular plugins and deep integration into third party tools. In the process, Rails has become mainstream,
attracting a more diverse set of developers to the framework.
This has led to a reorganization of the book. Many newcomers to Rails have
not had the pleasure of being introduced to Ruby, so this section has been
promoted from an appendix to a chapter in Part I. We follow Part I with a stepby-step walk through of building a real application, which has been updated
and streamlined to focus on current best practices. But the biggest change is
in the final part: as it is no longer practical to cover the entire ecosystem of
Rails given both its breadth and rate of change, this part is now focused on
providing an overall perspective of the landscape, enabling you, the reader, to
know what to look for and where to find plugins and related tools to address
common needs that go far beyond what the framework itself contains.
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