Ruby on Rails Tutorial

Learn Rails by Example

Michael Hartl

Contents

  1. Chapter 1 From zero to deploy
    1. 1.1 Introduction
      1. 1.1.1 Comments for various readers
      2. 1.1.2 “Scaling” Rails
      3. 1.1.3 Conventions in this book
    2. 1.2 Up and running
      1. 1.2.1 Development environments
        1. IDEs
        2. Text editors and command lines
        3. Browsers
        4. A note about tools
      2. 1.2.2 Ruby, RubyGems, and Rails
        1. Install Ruby
        2. Install RubyGems
        3. Install Rails
      3. 1.2.3 The first application
      4. 1.2.4 Model-view-controller (MVC)
      5. 1.2.5 script/server
    3. 1.3 Version control with Git
      1. 1.3.1 Installation and setup
        1. First-time system setup
        2. First-time repository setup
      2. 1.3.2 Adding and committing
      3. 1.3.3 What good does Git do you?
      4. 1.3.4 GitHub
      5. 1.3.5 Branch, edit, commit, merge
        1. Branch
        2. Edit
        3. Commit
        4. Merge
        5. Push
    4. 1.4 Deploying
      1. 1.4.1 Heroku setup
      2. 1.4.2 Heroku deployment, step one
      3. 1.4.3 Heroku deployment, step two
      4. 1.4.4 Heroku commands
    5. 1.5 Conclusion
  2. Chapter 2 A demo app
    1. 2.1 Planning the application
      1. 2.1.1 Modeling users
      2. 2.1.2 Modeling microposts
    2. 2.2 The Users resource
      1. 2.2.1 A user tour
      2. 2.2.2 MVC in action
      3. 2.2.3 Weaknesses of this Users resource
    3. 2.3 The Microposts resource
      1. 2.3.1 A micropost microtour
      2. 2.3.2 Putting the micro in microposts
      3. 2.3.3 A user has_many microposts
      4. 2.3.4 Inheritance hierarchies
      5. 2.3.5 Deploying the demo app
    4. 2.4 Conclusion
  3. Chapter 3 Mostly static pages
    1. 3.1 Static pages
      1. 3.1.1 Truly static pages
      2. 3.1.2 Static pages with Rails
    2. 3.2 Our first tests
      1. 3.2.1 Testing tools
        1. Installing RSpec
        2. Installing Autotest
      2. 3.2.2 TDD: Red, Green, Refactor
        1. Red
        2. Green
        3. Refactor
    3. 3.3 Slightly dynamic pages
      1. 3.3.1 Testing a title change
      2. 3.3.2 Passing title tests
      3. 3.3.3 Instance variables and Embedded Ruby
      4. 3.3.4 Eliminating duplication with layouts
    4. 3.4 Conclusion
    5. 3.5 Exercises
  4. Chapter 4 Rails-flavored Ruby
    1. 4.1 Motivation
      1. 4.1.1 A title helper
      2. 4.1.2 Cascading Style Sheets
    2. 4.2 Strings and methods
      1. 4.2.1 Comments
      2. 4.2.2 Strings
        1. Printing
        2. Single-quoted strings
      3. 4.2.3 Objects and message passing
      4. 4.2.4 Method definitions
      5. 4.2.5 Back to the title helper
    3. 4.3 Other data structures
      1. 4.3.1 Arrays and ranges
      2. 4.3.2 Blocks
      3. 4.3.3 Hashes and symbols
      4. 4.3.4 CSS revisited
    4. 4.4 Ruby classes
      1. 4.4.1 Constructors
      2. 4.4.2 Class inheritance
      3. 4.4.3 Modifying built-in classes
      4. 4.4.4 A controller class
      5. 4.4.5 A user class
    5. 4.5 Exercises
  5. Chapter 5 Filling in the layout
    1. 5.1 Adding some structure
      1. 5.1.1 Site navigation
      2. 5.1.2 Custom CSS
      3. 5.1.3 Partials
    2. 5.2 Layout links
      1. 5.2.1 Integration tests
      2. 5.2.2 Rails routes
      3. 5.2.3 Named routes
    3. 5.3 User signup: A first step
      1. 5.3.1 Users controller
      2. 5.3.2 Signup URL
    4. 5.4 Conclusion
    5. 5.5 Exercises
  6. Chapter 6 Modeling and viewing users, part I
    1. 6.1 User model
      1. 6.1.1 Database migrations
      2. 6.1.2 The model file
        1. Model annotation
        2. Accessible attributes
      3. 6.1.3 Creating user objects
      4. 6.1.4 Finding user objects
      5. 6.1.5 Updating user objects
    2. 6.2 User validations
      1. 6.2.1 Validating presence
      2. 6.2.2 Length validation
      3. 6.2.3 Format validation
      4. 6.2.4 Uniqueness validation
        1. The uniqueness caveat
    3. 6.3 Viewing users
      1. 6.3.1 Debug and Rails environments
      2. 6.3.2 User model, view, controller
      3. 6.3.3 A Users resource
    4. 6.4 Conclusion
    5. 6.5 Exercises
  7. Chapter 7 Modeling and viewing users, part II
    1. 7.1 Insecure passwords
      1. 7.1.1 Password validations
      2. 7.1.2 A password migration
      3. 7.1.3 An Active Record callback
    2. 7.2 Secure passwords
      1. 7.2.1 A secure password test
      2. 7.2.2 Some secure password theory
      3. 7.2.3 Implementing has_password?
      4. 7.2.4 An authenticate method
    3. 7.3 Better user views
      1. 7.3.1 Testing the user show page (with factories)
      2. 7.3.2 A name and a Gravatar
      3. 7.3.3 A user sidebar
    4. 7.4 Conclusion
      1. 7.4.1 Git commit
      2. 7.4.2 Heroku deploy
    5. 7.5 Exercises
  8. Chapter 8 Sign up
    1. 8.1 Signup form
      1. 8.1.1 Using form_for
      2. 8.1.2 The form HTML
    2. 8.2 Signup failure
      1. 8.2.1 Testing failure
      2. 8.2.2 A working form
      3. 8.2.3 Signup error messages
      4. 8.2.4 Filtering parameter logging
    3. 8.3 Signup success
      1. 8.3.1 Testing success
      2. 8.3.2 The finished signup form
      3. 8.3.3 The flash
      4. 8.3.4 The first signup
    4. 8.4 RSpec integration tests
      1. 8.4.1 Webrat
      2. 8.4.2 Users signup failure should not make a new user
      3. 8.4.3 Users signup success should make a new user
    5. 8.5 Conclusion
    6. 8.6 Exercises
  9. Chapter 9 Sign in, sign out
    1. 9.1 Sessions
      1. 9.1.1 Sessions controller
      2. 9.1.2 Signin form
    2. 9.2 Signin failure
      1. 9.2.1 Reviewing form submission
      2. 9.2.2 Failed signin (test and code)
    3. 9.3 Signin success
      1. 9.3.1 The completed create action
      2. 9.3.2 Remember me
      3. 9.3.3 Cookies
      4. 9.3.4 Current user
    4. 9.4 Signing out
      1. 9.4.1 Destroying sessions
      2. 9.4.2 Signin upon signup
      3. 9.4.3 Changing the layout links
      4. 9.4.4 Signin/out integration tests
    5. 9.5 Conclusion
    6. 9.6 Exercises
  10. Chapter 10 Updating, showing, and deleting users
    1. 10.1 Updating users
      1. 10.1.1 Edit form
      2. 10.1.2 Enabling edits
    2. 10.2 Protecting pages
      1. 10.2.1 Requiring signed-in users
      2. 10.2.2 Requiring the right user
      3. 10.2.3 An expectation bonus
      4. 10.2.4 Friendly forwarding
    3. 10.3 Showing users
      1. 10.3.1 User index
      2. 10.3.2 Sample users
      3. 10.3.3 Pagination
        1. Testing pagination
      4. 10.3.4 Partial refactoring
    4. 10.4 Destroying users
      1. 10.4.1 Administrative users
        1. Revisiting attr_accessible
      2. 10.4.2 The destroy action
    5. 10.5 Conclusion
    6. 10.6 Exercises
  11. Chapter 11 User microposts
    1. 11.1 A Micropost model
      1. 11.1.1 The basic model
        1. Accessible attribute
      2. 11.1.2 User/Micropost associations
      3. 11.1.3 Micropost refinements
        1. Default scope
        2. Dependent: destroy
      4. 11.1.4 Micropost validations
    2. 11.2 Showing microposts
      1. 11.2.1 Augmenting the user show page
      2. 11.2.2 Sample microposts
    3. 11.3 Manipulating microposts
      1. 11.3.1 Access control
      2. 11.3.2 Creating microposts
      3. 11.3.3 A proto-feed
      4. 11.3.4 Destroying microposts
      5. 11.3.5 Testing the new home page
    4. 11.4 Conclusion
    5. 11.5 Exercises
  12. Chapter 12 Following users
    1. 12.1 The Relationship model
      1. 12.1.1 A problem with the data model (and a solution)
      2. 12.1.2 User/relationship associations
      3. 12.1.3 Validations
      4. 12.1.4 Following
      5. 12.1.5 Followers
    2. 12.2 A web interface for following and followers
      1. 12.2.1 Sample following data
      2. 12.2.2 Stats and a follow form
      3. 12.2.3 Following and followers pages
      4. 12.2.4 A working follow button the standard way
      5. 12.2.5 A working follow button with Ajax
    3. 12.3 The status feed
      1. 12.3.1 Motivation and strategy
      2. 12.3.2 A first feed implementation
      3. 12.3.3 Scopes, subselects, and a lambda
      4. 12.3.4 The new status feed
    4. 12.4 Conclusion
      1. 12.4.1 Extensions to the sample application
        1. Replies
        2. Messaging
        3. Follower notifications
        4. Password reminders
        5. Signup confirmation
        6. RSS feed
        7. REST API
        8. Search
      2. 12.4.2 Guide to further resources
    5. 12.5 Exercises

Foreword

My former company (CD Baby) was one of the first to loudly switch to Ruby on Rails, and then even more loudly switch back to PHP (Google me to read about the drama). This book by Michael Hartl came so highly recommended that I had to try it, and Ruby on Rails Tutorial is what I used to switch back to Rails again.

Though I’ve worked my way through many Rails books, this is the one that finally made me “get” it. Everything is done very much “the Rails way”—a way that felt very unnatural to me before, but now after doing this book finally feels natural. This is also the only Rails book that does test-driven development the entire time, an approach highly recommended by the experts but which has never been so clearly demonstrated before. Finally, by including Git, GitHub, and Heroku in the demo examples, the author really gives you a feel for what it’s like to do a real-world project. The tutorial’s code examples are not in isolation.

The linear narrative is such a great format. Personally, I powered through Rails Tutorial in three long days, doing all the examples and challenges at the end of each chapter. Do it from start to finish, without jumping around, and you’ll get the ultimate benefit.

Enjoy!

Derek Sivers (sivers.org)
Formerly: Founder, CD Baby
Currently: Founder, Thoughts Ltd.

Acknowledgments

Ruby on Rails Tutorial owes a lot to my previous Rails book, RailsSpace, and hence to my coauthor Aurelius Prochazka. I’d like to thank Aure both for the work he did on that book and for his support of this one. I’d also like to thank Debra Williams Cauley, my editor on both RailsSpace and Rails Tutorial; as long as she keeps taking me to baseball games, I’ll keep writing books for her.

I’d like to acknowledge a long list of Rubyists who have taught and inspired me over the years: David Heinemeier Hansson, Yehuda Katz, Carl Lerche, Jeremy Kemper, Xavier Noria, Ryan Bates, Geoffrey Grosenbach, Peter Cooper, Matt Aimonetti, Gregg Pollack, Wayne E. Seguin, Amy Hoy, Dave Chelimsky, Pat Maddox, Tom Preston-Werner, Chris Wanstrath, Chad Fowler, Josh Susser, Obie Fernandez, Ian McFarland, Steven Bristol, Giles Bowkett, Evan Dorn, Long Nguyen, James Lindenbaum, Adam Wiggins, Tikhon Bernstam, Ron Evans, Wyatt Greene, Miles Forrest, the good people at Pivotal Labs, the Heroku gang, the thoughtbot guys, and the GitHub crew. Finally, many, many readers—far too many to list—have contributed a huge number of bug reports and suggestions during the writing of this book, and I gratefully acknowledge their help in making it as good as it can be.

About the author

Michael Hartl is a programmer, educator, and entrepreneur. Michael was coauthor of RailsSpace, a best-selling Rails tutorial book published in 2007, and was cofounder and lead developer of Insoshi, a popular social networking platform in Ruby on Rails. Previously, he taught theoretical and computational physics at the California Institute of Technology (Caltech), where he received the Lifetime Achievement Award for Excellence in Teaching. Michael is a graduate of Harvard College, has a Ph.D. in Physics from Caltech, and is an alumnus of the Y Combinator program.

Copyright and license

Ruby on Rails Tutorial: Learn Rails by Example. Copyright © 2010 by Michael Hartl. All source code in Ruby on Rails Tutorial is available under the MIT License and the Beerware License.

   Copyright (c) 2010 Michael Hartl

   Permission is hereby granted, free of charge, to any person
   obtaining a copy of this software and associated documentation
   files (the "Software"), to deal in the Software without
   restriction, including without limitation the rights to use,
   copy, modify, merge, publish, distribute, sublicense, and/or sell
   copies of the Software, and to permit persons to whom the
   Software is furnished to do so, subject to the following
   conditions:

   The above copyright notice and this permission notice shall be
   included in all copies or substantial portions of the Software.

   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
   OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
   NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
   HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
   WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
   FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
   OTHER DEALINGS IN THE SOFTWARE.
/*
 * ---------------------------------------------------------------------------
 * "THE BEERWARE LICENSE" (Revision 42):
 * Michael Hartl wrote this code. As long as you retain this notice, you can
 * do whatever you want with this stuff. If we meet someday, and you think
 * this stuff is worth it, you can buy me a beer in return.
 * ---------------------------------------------------------------------------
 */

Chapter 2 A demo app

In this chapter, we’ll develop a simple demonstration application to show off some of the power of Rails. The purpose is to get a high-level overview of Ruby on Rails programming (and web development in general) by rapidly generating an application using scaffold generators.1 As discussed in Box 1.1, the rest of the book will take the opposite approach, developing a full application incrementally and explaining each new concept as it arises, but for a quick overview (and some instant gratification) there is no substitute for scaffolding. The resulting demo app will allow us to interact with it through its URLs, giving us insight into the structure of a Rails application, including a first example of the REST architecture favored by Rails.

As with the forthcoming sample application, the demo app will consist of users and their associated microposts (thus constituting a minimalist Twitter-style app). The functionality will be utterly under-developed, and many of the steps will seem like magic, but worry not: the full sample app will develop a similar application from the ground up starting in Chapter 3, and I will provide plentiful forward-references to later material. In the mean time, have patience and a little faith—the whole point of this tutorial is to take you beyond this superficial, scaffold-driven approach to achieve a deeper understanding of Rails.

2.1 Planning the application

In this section we’ll outline our plans for the demo application. As in Section 1.2.3, we’ll start by generating the application skeleton using the rails command:

$ cd ~/rails_projects
$ rails demo_app
$ cd demo_app

Next, we’ll copy the .gitignore file from Listing 1.2 to the demo app’s Rails root directory:

$ git init
$ cp ~/rails_projects/first_app/.gitignore .
$ git add .
$ git commit -m "Initial commit"
create_demo_repo
Figure 2.1: Creating a demo app repository at GitHub. (full size)

You can also optionally create a new repository (Figure 2.1) and push it up to GitHub:

$ git remote add origin git@github.com:<username>/demo_app.git
$ git push origin master

Now we’re ready to start making the app itself. The typical first step when making a web application is to create a data model, which is a representation of the structures needed by our application. In our case, the demo app will be a stripped-down microblog, with only users and short (micro) posts. Thus, we’ll begin with a model for users of the app (Section 2.1.1), and then we’ll add a model for microposts (Section 2.1.2).

2.1.1 Modeling users

There are as many choices for a user data model as there are different registration forms on the web; we’ll go with a distinctly minimalist approach. Users of our demo app will have a unique integer identifier called id, a publicly viewable name (of type string), and an email address (also a string) that will double as a username. A summary of the data model for users appears in Figure 2.2.

demo_user_model
Figure 2.2: The data model for users.

As we’ll see starting in Section 6.1.1, the label users in Figure 2.2 corresponds to a table in a database, and the id, name, and email attributes are columns in that table.

2.1.2 Modeling microposts

The core of the micropost data model is even simpler than the one for users: a micropost has only an id and a content field for the micropost’s text (of type string).2 There’s an additional complication, though: we want to associate each micropost with a particular user; we’ll accomplish this by recording the user_id of the owner of the post. The results are shown in Figure 2.3.

demo_micropost_model
Figure 2.3: The data model for microposts.

We’ll see in Section 2.3.3 (and more fully in Chapter 11) how this user_id attribute allows us to succinctly express the notion that a user potentially has many associated microposts.

2.2 The Users resource

In this section, we’ll implement the users data model in Section 2.1.1, along with a web interface to that model. The combination will constitute a Users resource, which will allow us to think of users as objects that can be created, read, updated, and deleted through the web via the HTTP protocol.

As promised in the introduction, our Users resource will be created by a scaffold generator program, which comes standard with each Rails project. The argument of the scaffold command is the singular version of the resource name (in this case, User), together with optional parameters for the data model’s attributes:3

$ script/generate scaffold User name:string email:string
      exists  app/models/
      exists  app/controllers/
      exists  app/helpers/
      create  app/views/users
      exists  app/views/layouts/
      exists  test/functional/
      exists  test/unit/
      create  test/unit/helpers/
      exists  public/stylesheets/
      create  app/views/users/index.html.erb
      create  app/views/users/show.html.erb
      create  app/views/users/new.html.erb
      create  app/views/users/edit.html.erb
      create  app/views/layouts/users.html.erb
      create  public/stylesheets/scaffold.css
      create  app/controllers/users_controller.rb
      create  test/functional/users_controller_test.rb
      create  app/helpers/users_helper.rb
      create  test/unit/helpers/users_helper_test.rb
       route  map.resources :users
  dependency  model
      exists    app/models/
      exists    test/unit/
      exists    test/fixtures/
      create    app/models/user.rb
      create    test/unit/user_test.rb
      create    test/fixtures/users.yml
      create    db/migrate
      create    db/migrate/<timestamp>_create_users.rb

By including name:string and email:string, we have arranged for the User model to have the form shown in Figure 2.2. (Note that there is no need to include a parameter for id; it is created automatically by Rails.4)

To proceed with the demo application, we first need to migrate the database (a process mentioned briefly in Section 1.2.5):

$ rake db:migrate

This simply updates the database with our new users data model. We’ll learn more about database migrations starting in Section 6.1.1.

With that, we can run the local web server using

$ script/server

and the demo application should be ready to go at http://localhost:3000/.

2.2.1 A user tour

Visiting the root url http://localhost:3000/ shows the same default Rails page shown in Figure 1.5, but in generating the Users resource scaffolding we have also created a large number of pages for manipulating users. For example, the page for listing all users is at /users, and the page for making a new user is at /users/new.5 The rest of this section is dedicated to taking a whirlwind tour through these user pages. As we proceed, it may help to refer to Table 2.1, which shows the correspondence between pages and URLs.

URLActionPurpose
/usersindexpage to list all users
/users/1showpage to show user with id 1
/users/newnewpage to make a new user
/users/1/editeditpage to edit user with id 1
Table 2.1: The correspondence between pages and URLs for the Users resource.

We start with the page to show all the users in our application, called index; as you might expect, initially there are no users at all (Figure 2.4).

demo_blank_user_index
Figure 2.4: The initial index page for the Users resource (/users). (full size)

To make a new user, we visit the new page, as show in Figure 2.5. (In Chapter 8, this will become the user signup page.)

demo_new_user
Figure 2.5: The new user page (/users/new). (full size)

We can create a user by entering name and email values in the text fields and then clicking the Create button. The result is the user show page, as seen in Figure 2.6. (The green welcome message is accomplished using the flash, which we’ll learn about in Section 8.3.3.) Note that the URL is /users/1; as you might suspect, the number 1 is simply the user’s id attribute from Figure 2.2. In Section 7.3, this page will become the user’s profile.

demo_show_user
Figure 2.6: The page to show a user (/users/1). (full size)

To change a user’s information, we visit the edit page (Figure 2.7). By modifying the user information and clicking the Update button, we arrange to change the information for the user in the demo application (Figure 2.8). (As we’ll see in detail starting in Chapter 6, this user data is stored in a database back-end.) We’ll add user edit/update functionality to the sample application in Section 10.1.

demo_edit_user
Figure 2.7: The user edit page (/users/1/edit). (full size)
demo_update_user
Figure 2.8: A user with updated information. (full size)

Now we’ll create a second user by revisiting the new page and submitting a second set of user information; the resulting user index is shown in Figure 2.9. Section 10.3 will develop the user index into a more polished page for showing all users.

demo_user_index_two
Figure 2.9: The user index page (/users) with a second user. (full size)

Having shown how to create, show, and edit users, we come finally to destroying them (Figure 2.10). You should verify that clicking on the link in Figure 2.10 destroys the second user, yielding an index page with only one user. (If it doesn’t work, be sure that JavaScript is enabled in your browser; Rails uses JavaScript to issue the request needed to destroy a user.) Section 10.4 adds user deletion to the sample app, taking care to restrict its use to a special class of administrative users.

demo_destroy_user
Figure 2.10: Destroying a user. (full size)

2.2.2 MVC in action

Now that we’ve completed a quick overview of the Users resource, let’s examine one particular part of it in the context of the Model-View-Controller (MVC) pattern introduced in Section 1.2.4. Our strategy will be to describe the results of a typical browser hit—a visit to the user index page at /users—in terms of MVC (Figure 2.11).

mvc_detailed
Figure 2.11: A detailed diagram of MVC in Rails. (full size)

The steps in Figure 2.11

  1. The browser issues a request for the /users URL.
  2. Rails routes /users to the index action in the Users controller.
  3. The index action asks the User model to retrieve all users (User.all).
  4. The User model pulls all the users from the database.
  5. The User model returns the list of users to the controller.
  6. The controller captures the users in the @users variable, which is passed to the index view.
  7. The view uses Embedded Ruby to render the page as HTML.
  8. The controller passes the HTML back to the browser.6

We start with a request issued from the browser—i.e., the result of typing a URL in the address bar or clicking on a link (step 1 in Figure 2.11). This request hits the Rails router (step 2), which dispatches to the proper controller action based on the URL (and, as we’ll see in Box 3.1, the type of request). The code to create the mapping of user URLs to controller actions for the Users resource appears in Listing 2.1;7 this code effectively sets up the table of URL/action pairs seen in Table 2.1.

Listing 2.1. The Rails routes, with a rule for the Users resource.
config/routes.rb
ActionController::Routing::Routes.draw do |map|
  map.resources :users
  .
  .
  .
end

The pages from the tour in Section 2.2.1 correspond to actions in the Users controller, which is a collection of related actions; the controller generated by the scaffolding is shown schematically in Listing 2.2. Note the notation class UsersController < ApplicationController; this is an example of a Ruby class with inheritance. (We’ll discuss inheritance briefly in Section 2.3.4 and cover both subjects in more detail in Section 4.4.)

Listing 2.2. The Users controller in schematic form.
app/controllers/users_controller.rb
class UsersController < ApplicationController

  def index
    .
    .
    .
  end

  def show
    .
    .
    .
  end

  def new
    .
    .
    .
  end

  def create
    .
    .
    .
  end

  def edit
    .
    .
    .
  end

  def update
    .
    .
    .
  end

  def destroy
    .
    .
    .
  end
end

You may notice that there are more actions than there are pages; the index, show, new, and edit actions all correspond to pages from Section 2.2.1, but there are additional create, update, and destroy actions as well. These actions don’t typically render pages (although they sometimes do); instead, their main purpose is to modify information about users in the database. This full suite of controller actions, summarized in Table 2.2, represents the implementation of the REST architecture in Rails (Box 2.1). Note from Table 2.2 that there is some overlap in the URLs; for example, both the user show action and the update action correspond to the URL /users/1. The difference between them is the HTTP request method they respond to. We’ll learn more about HTTP request methods starting in Section 3.2.2.

HTTP requestURLActionPurpose
GET/usersindexpage to list all users
GET/users/1showpage to show user with id 1
GET/users/newnewpage to make a new user
POST/userscreatecreate a new user
GET/users/1/editeditpage to edit user with id 1
PUT/users/1updateupdate user with id 1
DELETE/users/1destroydelete user with id 1
Table 2.2: RESTful routes provided by the Users resource in Listing 2.1.

To examine the relationship between the Users controller and the User model, let’s focus on a simplified version of the index action, shown in Listing 2.3.8

Listing 2.3. The simplified user index action for the demo application.
app/controllers/users_controller.rb
class UsersController < ApplicationController

  def index
    @users = User.all
  end
  .
  .
  .
end

This index action has the line @users = User.all (step 3), which asks the User model to retrieve a list of all the users from the database (step 4), and then places them in the variable @users (pronounced “at-users”) (step 5). The User model itself appears in Listing 2.4; although it is rather plain, it comes equipped with a large amount of functionality because of inheritance (Section 2.3.4 and Section 4.4). In particular, by using the Rails library called Active Record, the code in Listing 2.4 arranges for User.all to return all the users.

Listing 2.4. The User model for the demo application.
app/models/user.rb
class User < ActiveRecord::Base
end

Once the @users variable is defined, the controller calls the view (step 6), shown in Listing 2.5. Variables that start with the @ sign, called instance variables, are automatically available in the view; in this case, the index.html.erb view in Listing 2.5 iterates through the @users list and outputs a line of HTML for each one.9

Listing 2.5. The view for the user index. (You are not expected to understand it now.)
app/views/users/index.html.erb
<h1>Listing users</h1>

<table>
  <tr>
    <th>Name</th>
    <th>Email</th>
  </tr>

<% @users.each do |user| %>
  <tr>
    <td><%=h user.name %></td>
    <td><%=h user.email %></td>
    <td><%= link_to 'Show', user %></td>
    <td><%= link_to 'Edit', edit_user_path(user) %></td>
    <td><%= link_to 'Destroy', user, :confirm => 'Are you sure?',
:method => :delete %></td>
  </tr>
<% end %>
</table>

<br />

<%= link_to 'New user', new_user_path %>

The view converts its contents to HTML (step 7), which is then returned by the controller to the browser for display (step 8).

2.2.3 Weaknesses of this Users resource

Though good for getting a general overview of Rails, the scaffold Users resource suffers from a number of severe weaknesses.

  • No data validations. Our User model accepts data such as blank names and invalid email addresses without complaint.
  • No authentication. We have no notion signing in or out, and no way to prevent any user from performing any operation.
  • No tests. This isn’t technically true—the scaffolding includes rudimentary tests—but the generated tests are ugly and inflexible, and they don’t test for data validation, authentication, or any other custom requirements.
  • No layout. There is no consistent site styling or navigation.
  • No real understanding. If you understand the scaffold code, you probably shouldn’t be reading this book.

2.3 The Microposts resource

Having generated and explored the Users resource, we turn now to the associated Microposts resource. Throughout this section, I recommend comparing the elements of the Microposts resource with the analogous user elements from Section 2.2; you should see that the two resources parallel each other in many ways. The RESTful structure of Rails applications is best absorbed by this sort of repetition of form; indeed, seeing the parallel structure of Users and Microposts even at this early stage is one of the prime motivations for this chapter. (As we’ll see, writing applications more robust than the toy example in this chapter takes considerable effort—we won’t see the Microposts resource again until Chapter 11—and I didn’t want to defer its first appearance quite that far.)

2.3.1 A micropost microtour

As with the Users resource, we’ll generate scaffold code for the Microposts resource using script/generate scaffold, in this case implementing the data model from Figure 2.3:10

$ script/generate scaffold Micropost content:string user_id:integer

To update our database with the new data model, we need to run a migration as in Section 2.2:

$ rake db:migrate

Now we are in a position to create microposts in the same way we created users in Section 2.2.1. As you might guess, the scaffold generator has updated the Rails routes file with a rule for Microposts resource, as seen in Listing 2.6.11 As with users, the map.resources :microposts routing rule maps a micropost URLs to actions in the Microposts controller, as seen in Table 2.3.

Listing 2.6. The Rails routes, with a new rule for Microposts resources.
config/routes.rb
ActionController::Routing::Routes.draw do |map|
  map.resources :users
  map.resources :microposts
  .
  .
  .
end
HTTP requestURLActionPurpose
GET/micropostsindexpage to list all microposts
GET/microposts/1showpage to show micropost with id 1
GET/microposts/newnewpage to make a new micropost
POST/micropostscreatecreate a new micropost
GET/microposts/1/editeditpage to edit micropost with id 1
PUT/microposts/1updateupdate micropost with id 1
DELETE/microposts/1destroydelete micropost with id 1
Table 2.3: RESTful routes provided by the Microposts resource in Listing 2.6.

The Microposts controller itself appears in schematic form Listing 2.7. Note that, apart from having MicropostsController in place of UsersController, Listing 2.7 is identical to the code in Listing 2.2. This is a reflection of the REST architecture common to both resources.

Listing 2.7. The Microposts controller in schematic form.
app/controllers/microposts_controller.rb
class MicropostsController < ApplicationController

  def index
    .
    .
    .
  end

  def show
    .
    .
    .
  end

  def new
    .
    .
    .
  end

  def create
    .
    .
    .
  end

  def edit
    .
    .
    .
  end

  def update
    .
    .
    .
  end

  def destroy
    .
    .
    .
  end
end

To make some actual microposts, we enter information at the new microposts page, /microposts/new, as seen in Figure 2.12.

demo_new_micropost
Figure 2.12: The new micropost page (/microposts/new). (full size)

At this point, go ahead and create a micropost or two, taking care to make sure that at least one has a user_id of 1 to match the id of the first user created in Section 2.2.1. The result should look something like Figure 2.13.

demo_micropost_index
Figure 2.13: The micropost index page (/microposts). (full size)

2.3.2 Putting the micro in microposts

Any micropost worthy of the name should have some means of enforcing the length of the post. Implementing this constraint in Rails is easy with validations; to accept microposts with at most 140 characters (à la Twitter), we use a length validation. At this point, you should open the file app/models/micropost.rb in your text editor or IDE and fill it with the contents of Listing 2.8.

Listing 2.8. Constraining microposts to at most 140 characters with a length validation.
app/models/micropost.rb
class Micropost < ActiveRecord::Base
  validates_length_of :content, :maximum => 140
end

At this point, the code in Listing 2.8 may look rather mysterious—we’ll cover validations more thoroughly starting in Section 6.2—but its effects are readily apparent if we go to the new micropost page and enter more than 140 characters for the content of the post. As seen in Figure 2.14, Rails renders error messages indicating that the micropost’s content is too long.12 (We’ll learn more about error messages in Section 8.2.3.)

micropost_length_error
Figure 2.14: Error messages for a failed micropost creation. (full size)

2.3.3 A user has_many microposts

One of the most powerful features of Rails is the ability to form associations between different data models. In the case of our User model, each user potentially has many microposts. We can express this in code by updating the User and Micropost models as in Listing 2.9 and Listing 2.10.

Listing 2.9. A user has many microposts.
app/models/user.rb
class User < ActiveRecord::Base
  has_many :microposts
end
Listing 2.10. A micropost belongs to a user.
app/models/micropost.rb
class Micropost < ActiveRecord::Base
  belongs_to :user

  validates_length_of :content, :maximum => 140
end

We can visualize the result of this association in Figure 2.15. Because of the user_id column in the microposts table, Rails (using Active Record) can infer the microposts associated with each user.

micropost_user_association
Figure 2.15: The association between microposts and users.

In Chapter 11 and Chapter 12, we will use the association of users and microposts both to display all a user’s microposts and to construct a Twitter-like micropost feed. For now, we can examine the implications of the user-micropost association by using the console, which is a useful tool for interacting with Rails applications. We first invoke the console with script/console at the command line, and then retrieve the first user from the database using User.first (putting the results in the variable first_user):

$ script/console
>> first_user = User.first
=> #<User id: 1, name: "Michael Hartl", email: "michael@example.org",
created_at: "2010-04-03 02:01:31", updated_at: "2010-04-03 02:01:31">
>> first_user.microposts
=> [#<Micropost id: 1, content: "First micropost!", user_id: 1, created_at:
"2010-04-03 02:37:37", updated_at: "2010-04-03 02:37:37">, #<Micropost id: 2,
content: "Second micropost", user_id: 1, created_at: "2010-04-03 02:38:54",
updated_at: "2010-04-03 02:38:54">]

Here we have accessed the user’s microposts using the code first_user.microposts: with this code, Active Record automatically returns all the microposts with user_id equal to the id of first_user (in this case, 1). We’ll learn much more about the association facilities in Active Record in Chapter 11 and Chapter 12.

2.3.4 Inheritance hierarchies

We end our discussion of the demo application with a brief description of the controller and model class hierarchies in Rails. This discussion will only make much sense if you have some experience with object-oriented programming (OOP); if you haven’t studied OOP, feel free to skip this section. In particular, if you are unfamiliar with classes (discussed in Section 4.4), I suggest looping back to this section at a later time.

We start with the inheritance structure for models. Comparing Listing 2.11 and Listing 2.12, we see that both the User model and the Micropost model inherit (via the left angle bracket <) from ActiveRecord::Base, which is the base class for models provided by ActiveRecord; a diagram summarizing this relationship appears in Figure 2.16. It is by inheriting from ActiveRecord::Base that our model objects gain the ability to communicate with the database, treat the database columns as Ruby attributes, and so on.

Listing 2.11. The User class, with inheritance.
app/models/user.rb
class User < ActiveRecord::Base
  .
  .
  .
end
Listing 2.12. The Micropost class, with inheritance.
app/models/micropost.rb
class Micropost < ActiveRecord::Base
  .
  .
  .
end
demo_model_inheritance
Figure 2.16: The inheritance hierarchy for the User and Micropost models.

The inheritance structure for controllers is only slightly more complicated. Comparing Listing 2.13 and Listing 2.14, we see that both the Users controller and the Microposts controller inherit from the Application controller. Examining Listing 2.15, we see that ApplicationController itself inherits from ActionController::Base; this is the base class for controllers provided by the Rails library Action Pack. The relationships between these classes is illustrated in Figure 2.17.

Listing 2.13. The UsersController class, with inheritance.
app/controllers/users_controller.rb
class UsersController < ApplicationController
  .
  .
  .
end
Listing 2.14. The MicropostsController class, with inheritance.
app/controllers/microposts_controller.rb
class MicropostsController < ApplicationController
  .
  .
  .
end
Listing 2.15. The ApplicationController class, with inheritance.
app/controllers/application_controller.rb
class ApplicationController < ActionController::Base
  .
  .
  .
end
demo_controller_inheritance
Figure 2.17: The inheritance hierarchy for the Users and Microposts controllers.

As with model inheritance, by inheriting ultimately from ActionController::Base both the Users and Microposts controllers gain a large amount of functionality, such as the ability to manipulate model objects, filter inbound HTTP requests, and render views as HTML. Since all Rails controllers inherit from ApplicationController, rules defined in the Application controller automatically apply to every action in the application. For example, in Section 8.2.4 we’ll define a rule in the Application controller to filter passwords from all the Rails log files, thereby avoiding a serious potential security breach.

2.3.5 Deploying the demo app

With the completion of the Microposts resource, now is a good time to push the repository up to GitHub:13

$ git add .
$ git commit -a -m "Done with the demo app"
$ git push

You can also deploy the demo app to Heroku:

$ heroku create
$ git push heroku master
$ heroku rake db:migrate

Note the final line here, which runs the database migrations on the Heroku server. This updates the database at Heroku with the necessary user/micropost data model. If you want to push the data up, too, you can do so using the taps gem and db:push:

$ [sudo] gem install taps
$ heroku db:push

2.4 Conclusion

We’ve come now to the end of the 30,000-foot view of a Rails application. The demo app developed in this chapter has several strengths and a host of weaknesses.

Strengths

  • High-level overview of Rails
  • Introduction to MVC
  • First taste of the REST architecture
  • Beginning data modeling
  • A live, database-backed web application in production14

Weaknesses

  • No custom layout or styling
  • No static pages (like “Home” or “About”)
  • No user passwords
  • No user images
  • No signing in
  • No security
  • No automatic user/micropost association
  • No notion of “following” or “followed”
  • No micropost feed
  • No test-driven development
  • No real understanding

The rest of this tutorial is dedicated to building on the strengths and eliminating the weaknesses.

  1. I urge you not to look too closely at the generated code; at this stage, it will only serve to confuse you. 
  2. When modeling longer posts, such as those for a normal (non-micro) blog, you should use the text type in place of string
  3. The name of the scaffold follows the convention of models, which are singular, rather than resources and controllers, which are plural. Thus, we have User instead Users
  4. The user id is needed as the primary key in the database. 
  5. Since the http://localhost:3000 part of the address is implicit whenever we are developing locally, I’ll usually omit it from now on. 
  6. Some references indicate that the view returns the HTML directly to the browser (via a web server such as Apache or Nginx). Regardless of the implementation details, I prefer to think of the controller as a central hub through which all the application’s information flows. 
  7. The strange notation :users is a symbol, which we’ll learn about in Section 4.3.3
  8. The scaffold code is ugly and confusing, so I’ve suppressed it. 
  9. Remember, you aren’t supposed to understand this code right now. It is shown only for purposes of illustration. 
  10. As with the User scaffold, the scaffold generator for microposts follows the singular convention of Rails models; thus, we have generate Micropost
  11. The scaffold code may have extra newlines compared to Listing 2.6; this is not a cause for concern, as Ruby ignores extra newlines. 
  12. You might notice that the HTML Validator indicates an error; annoyingly, the default Rails error messages are not valid HTML. 
  13. Ordinarily, you should make smaller, more frequent commits, but for the purposes of this chapter a single big commit at the end is just fine. 
  14. If you deployed to Heroku in Section 2.3.5
Michael Hartl is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.