h2. Getting Started with Rails This guide covers getting up and running with Ruby on Rails. After reading it, you should be familiar with: * Installing Rails, creating a new Rails application, and connecting your application to a database * The general layout of a Rails application * The basic principles of MVC (Model, View Controller) and RESTful design * How to quickly generate the starting pieces of a Rails application endprologue. WARNING. This Guide is based on Rails 3.2. Some of the code shown here will not work in earlier versions of Rails. WARNING: The Edge version of this guide is currently being re-worked. Please excuse us while we re-arrange the place. h3. Guide Assumptions This guide is designed for beginners who want to get started with a Rails application from scratch. It does not assume that you have any prior experience with Rails. However, to get the most out of it, you need to have some prerequisites installed: * The "Ruby":http://www.ruby-lang.org/en/downloads language version 1.8.7 or higher TIP: Note that Ruby 1.8.7 p248 and p249 have marshaling bugs that crash Rails 3.0. Ruby Enterprise Edition have these fixed since release 1.8.7-2010.02 though. On the 1.9 front, Ruby 1.9.1 is not usable because it outright segfaults on Rails 3.0, so if you want to use Rails 3 with 1.9.x jump on 1.9.2 or 1.9.3 for smooth sailing. * The "RubyGems":http://rubyforge.org/frs/?group_id=126 packaging system ** If you want to learn more about RubyGems, please read the "RubyGems User Guide":http://docs.rubygems.org/read/book/1 * A working installation of the "SQLite3 Database":http://www.sqlite.org Rails is a web application framework running on the Ruby programming language. If you have no prior experience with Ruby, you will find a very steep learning curve diving straight into Rails. There are some good free resources on the internet for learning Ruby, including: * "Mr. Neighborly's Humble Little Ruby Book":http://www.humblelittlerubybook.com * "Programming Ruby":http://www.ruby-doc.org/docs/ProgrammingRuby/ * "Why's (Poignant) Guide to Ruby":http://mislav.uniqpath.com/poignant-guide/ h3. What is Rails? Rails is a web application development framework written in the Ruby language. It is designed to make programming web applications easier by making assumptions about what every developer needs to get started. It allows you to write less code while accomplishing more than many other languages and frameworks. Experienced Rails developers also report that it makes web application development more fun. Rails is opinionated software. It makes the assumption that there is a "best" way to do things, and it's designed to encourage that way - and in some cases to discourage alternatives. If you learn "The Rails Way" you'll probably discover a tremendous increase in productivity. If you persist in bringing old habits from other languages to your Rails development, and trying to use patterns you learned elsewhere, you may have a less happy experience. The Rails philosophy includes two major guiding principles: * DRY - "Don't Repeat Yourself" - suggests that writing the same code over and over again is a bad thing. * Convention Over Configuration - means that Rails makes assumptions about what you want to do and how you're going to do it, rather than requiring you to specify every little thing through endless configuration files. h3. Creating a New Rails Project The best way to use this guide is to follow each step as it happens, no code or step needed to make this example application has been left out, so you can literally follow along step by step. You can get the complete code "here":https://github.com/lifo/docrails/tree/master/guides/code/getting_started. By following along with this guide, you'll create a Rails project called +blog+, a (very) simple weblog. Before you can start building the application, you need to make sure that you have Rails itself installed. TIP: The examples below use # and $ to denote terminal prompts. If you are using Windows, your prompt will look something like c:\source_code> h4. Installing Rails To install Rails, use the +gem install+ command provided by RubyGems: # gem install rails TIP. A number of tools exist to help you quickly install Ruby and Ruby on Rails on your system. Windows users can use "Rails Installer":http://railsinstaller.org, while Mac OS X users can use "Rails One Click":http://railsoneclick.com. To verify that you have everything installed correctly, you should be able to run the following: $ rails --version If it says something like "Rails 3.2.3" you are ready to continue. h4. Creating the Blog Application Rails comes with a number of generators that are designed to make your development life easier. One of these is the new application generator, which will provide you with the foundation of a Rails application so that you don't have to write it yourself. To use this generator, open a terminal, navigate to a directory where you have rights to create files, and type: $ rails new blog This will create a Rails application called Blog in a directory called blog. TIP: You can see all of the command line options that the Rails application builder accepts by running +rails new -h+. After you create the blog application, switch to its folder to continue work directly in that application: $ cd blog The +rails new blog+ command we ran above created a folder in your working directory called +blog+. The +blog+ directory has a number of auto-generated files and folders that make up the structure of a Rails application. Most of the work in this tutorial will happen in the +app/+ folder, but here's a basic rundown on the function of each of the files and folders that Rails created by default: |_.File/Folder|_.Purpose| |app/|Contains the controllers, models, views, helpers, mailers and assets for your application. You'll focus on this folder for the remainder of this guide.| |config/|Configure your application's runtime rules, routes, database, and more. This is covered in more detail in "Configuring Rails Applications":configuring.html| |config.ru|Rack configuration for Rack based servers used to start the application.| |db/|Contains your current database schema, as well as the database migrations.| |doc/|In-depth documentation for your application.| |Gemfile
Gemfile.lock|These files allow you to specify what gem dependencies are needed for your Rails application. These files are used by the Bundler gem. For more information about Bundler, see "the Bundler website":http://gembundler.com | |lib/|Extended modules for your application.| |log/|Application log files.| |public/|The only folder seen to the world as-is. Contains the static files and compiled assets.| |Rakefile|This file locates and loads tasks that can be run from the command line. The task definitions are defined throughout the components of Rails. Rather than changing Rakefile, you should add your own tasks by adding files to the lib/tasks directory of your application.| |README.rdoc|This is a brief instruction manual for your application. You should edit this file to tell others what your application does, how to set it up, and so on.| |script/|Contains the rails script that starts your app and can contain other scripts you use to deploy or run your application.| |test/|Unit tests, fixtures, and other test apparatus. These are covered in "Testing Rails Applications":testing.html| |tmp/|Temporary files| |vendor/|A place for all third-party code. In a typical Rails application, this includes Ruby Gems and the Rails source code (if you optionally install it into your project).| h3. Hello, Rails! To begin with, let's get some text up on screen quickly. To do this, you need to get your Rails application server running. h4. Starting up the Web Server You actually have a functional Rails application already. To see it, you need to start a web server on your development machine. You can do this by running: $ rails server TIP: Compiling CoffeeScript to JavaScript requires a JavaScript runtime and the absence of a runtime will give you an +execjs+ error. Usually Mac OS X and Windows come with a JavaScript runtime installed. Rails adds the +therubyracer+ gem to Gemfile in a commented line for new apps and you can uncomment if you need it. +therubyrhino+ is the recommended runtime for JRuby users and is added by default to Gemfile in apps generated under JRuby. You can investigate about all the supported runtimes at "ExecJS":https://github.com/sstephenson/execjs#readme. This will fire up WEBrick, a webserver built into Ruby by default. To see your application in action, open a browser window and navigate to "http://localhost:3000":http://localhost:3000. You should see the Rails default information page: !images/rails_welcome.png(Welcome Aboard screenshot)! TIP: To stop the web server, hit Ctrl+C in the terminal window where it's running. In development mode, Rails does not generally require you to restart the server; changes you make in files will be automatically picked up by the server. The "Welcome Aboard" page is the _smoke test_ for a new Rails application: it makes sure that you have your software configured correctly enough to serve a page. You can also click on the _About your application’s environment_ link to see a summary of your application's environment. h4. Say "Hello", Rails To get Rails saying "Hello", you need to create at minimum a _controller_ and a _view_. A controller's purpose is to receive specific requests for the application. _Routing_ decides which controller receives which requests. Often, there is more than one route to each controller, and different routes can be served by different _actions_. Each action's purpose is to collect information to provide it to a view. A view's purpose is to display this information in a human readable format. An important distinction to make is that it is the _controller_, not the view, where information is collected. The view should just display that information. By default, view templates are written in a language called ERB (Embedded Ruby) which is converted by the request cycle in Rails before being sent to the user. To create a new controller, you will need to run the "controller" generator and tell it you want a controller called "welcome" with an action called "index", just like this: $ rails generate controller welcome index Rails will create several files for you. Most important of these are of course the controller, located at +app/controllers/welcome_controller.rb+ and the view, located at +app/views/welcome/index.html.erb+. Open the +app/views/welcome/index.html.erb+ file in your text editor and edit it to contain a single line of code:

Hello, Rails!

h4. Setting the Application Home Page Now that we have made the controller and view, we need to tell Rails when we want "Hello Rails!" to show up. In our case, we want it to show up when we navigate to the root URL of our site, "http://localhost:3000":http://localhost:3000. At the moment, however, the "Welcome Aboard" smoke test is occupying that spot. To fix this, delete the +index.html+ file located inside the +public+ directory of the application. You need to do this because Rails will serve any static file in the +public+ directory that matches a route in preference to any dynamic content you generate from the controllers. The +index.html+ file is special: it will be served if a request comes in at the root route, e.g. http://localhost:3000. If another request such as http://localhost:3000/welcome happened, a static file at public/welcome.html would be served first, but only if it existed. Next, you have to tell Rails where your actual home page is located. Open the file +config/routes.rb+ in your editor. This is your application's _routing file_ which holds entries in a special DSL (domain-specific language) that tells Rails how to connect incoming requests to controllers and actions. This file contains many sample routes on commented lines, and one of them actually shows you how to connect the root of your site to a specific controller and action. Find the line beginning with +root :to+ and uncomment it. It should look something like the following: Blog::Application.routes.draw do #... # You can have the root of your site routed with "root" # just remember to delete public/index.html. root :to => "welcome#index" The +root :to => "welcome#index"+ tells Rails to map requests to the root of the application to the welcome controller's index action. This was created earlier when you ran the controller generator (+rails generate controller welcome index+). If you navigate to "http://localhost:3000":http://localhost:3000 in your browser, you'll see the +Hello, Rails!+ message you put into +app/views/welcome/index.html.erb+, indicating that this new route is indeed going to +WelcomeController+'s +index+ action and is rendering the view correctly. NOTE. For more information about routing, refer to "Rails Routing from the Outside In":routing.html. h3. Getting Up and Running Now that you've seen how to create a controller, an action and a view, let's create something with a bit more substance. In the Blog application, you will now create a new _resource_. A resource is the term used for a collection of similar objects, such as posts, people or animals. You can create, read, update and destroy items for a resource and these operations are referred to as _CRUD_ operations. In the next section, you will add the ability to create new posts in your application and be able to view them. This is the "C" and the "R" from CRUD: creation and reading. The form for doing this will look like this: !images/getting_started/new_post.png(The new post form)! It will look a little basic for now, but that's ok. We'll look at improving the styling for it afterwards. h4. Laying down the ground work The first thing that you are going to need to create a new post within the application is a place to do that. A great place for that would be at +/posts/new+. If you attempt to navigate to that now -- by visiting "http://localhost:3000/posts/new":http://localhost:3000/posts/new -- Rails will give you a routing error: !images/getting_started/routing_error_no_route_matches.png(A routing error, no route matches /posts/new)! This is because there is nowhere inside the routes for the application -- defined inside +config/routes.rb+ -- that defines this route. By default, Rails has no routes configured at all, besides the root route you defined earlier, and so you must define your routes as you need them. To do this, you're going to need to create a route inside +config/routes.rb+ file, on a new line between the +do+ and the +end+ for the +draw+ method: get "posts/new" This route is a super-simple route: it defines a new route that only responds to +GET+ requests, and that the route is at +posts/new+. But how does it know where to go without the use of the +:to+ option? Well, Rails uses a sensible default here: Rails will assume that you want this route to go to the new action inside the posts controller. With the route defined, requests can now be made to +/posts/new+ in the application. Navigate to "http://localhost:3000/posts/new":http://localhost:3000/posts/new and you'll see another routing error: !images/getting_started/routing_error_no_controller.png(Another routing error, uninitialized constant PostsController)! This error is happening because this route need a controller to be defined. The route is attempting to find that controller so it can serve the request, but with the controller undefined, it just can't do that. The solution to this particular problem is simple: you need to create a controller called +PostsController+. You can do this by running this command: $ rails g controller posts If you open up the newly generated +app/controllers/posts_controller.rb+ you'll see a fairly empty controller: class PostsController < ApplicationController end A controller is simply a class that is defined to inherit from +ApplicationController+. It's inside this class that you'll define methods that will become the actions for this controller. These actions will perform CRUD operations on the posts within our system. If you refresh "http://localhost:3000/posts/new":http://localhost:3000/posts/new now, you'll get a new error: !images/getting_started/unknown_action_new_for_posts.png(Unknown action new for PostsController!)! This error indicates that Rails cannot find the +new+ action inside the +PostsController+ that you just generated. This is because when controllers are generated in Rails they are empty by default, unless you tell it you wanted actions during the generation process. To manually define an action inside a controller, all you need to do is to define a new method inside the controller. Open +app/controllers/posts_controller.rb+ and inside the +PostsController+ class, define a +new+ method like this: def new end With the +new+ method defined in +PostsController+, if you refresh "http://localhost:3000/posts/new":http://localhost:3000/posts/new you'll see another error: !images/getting_started/template_is_missing_posts_new.png(Template is missing for posts/new)! You're getting this error now because Rails expects plain actions like this one to have views associated with them to display their information. With no view available, Rails errors out. In the above image, the bottom line has been truncated. Let's see what the full thing looks like:
Missing template posts/new, application/new with {:locale=>[:en], :formats=>[:html], :handlers=>[:erb, :builder, :coffee]}. Searched in: * "/path/to/blog/app/views"
That's quite a lot of text! Let's quickly go through and understand what each part of it does. The first part identifies what template is missing. In this case, it's the +posts/new+ template. Rails will first look for this template. If not found, then it will attempt to load a template called +application/new+. It looks for one here because the +PostsController+ inherits from +ApplicationController+. The next part of the message contains a hash. The +:locale+ key in this hash simply indicates what spoken language template should be retrieved. By default, this is the English -- or "en" -- template. The next key, +:formats+ specifies the format of template to be served in response . The default format is +:html+, and so Rails is looking for an HTML template. The final key, +:handlers+, is telling us what _template handlers_ could be used to render our template. +:erb+ is most commonly used for HTML templates, +:builder+ is used for XML templates, and +:coffee+ uses CoffeeScript to build JavaScript templates. The final part of this message tells us where Rails has looked for the templates. Templates within a basic Rails application like this are kept in a single location, but in more complex applications it could be many different paths. The simplest template that would work in this case would be one located at +app/views/posts/new.html.erb+. The extension of this file name is key: the first extension is the _format_ of the template, and the second extension is the _handler_ that will be used. Rails is attempting to find a template called +posts/new+ within +app/views+ for the application. The format for this template can only be +html+ and the handler must be one of +erb+, +builder+ or +coffee+. Because you want to create a new HTML form, you will be using the +ERB+ language. Therefore the file should be called +posts/new.html.erb+ and needs to be located inside the +app/views+ directory of the application. Go ahead now and create a new file at +app/views/posts/new.html.erb+ and write this content in it:

New Post

When you refresh "http://localhost:3000/posts/new":http://localhost:3000/posts/new you'll now see that the page has a title. The route, controller, action and view are now working harmoniously! It's time to create the form for a new post. h4. The first form To create a form within this template, you will use a form builder. The primary form builder for Rails is provided by a helper method called +form_for+. To use this method, add this code into +app/views/posts/new.html.erb+: <%= form_for :post do |f| %>

<%= f.label :title %>
<%= f.text_field :title %>

<%= f.label :text %>
<%= f.text_area :text %>

<%= f.submit %>

<% end %>
If you refresh the page now, you'll see the exact same form as in the example. Building forms in Rails is really just that easy! When you call +form_for+, you pass it an identifying object for this form. In this case, it's the symbol +:post+. This tells the +form_for+ helper what this form is for. Inside the block for this method, the +FormBuilder+ object -- represented by +f+ -- is used to build two labels and two text fields, one each for the title and text of a post. Finally, a call to +submit+ on the +f+ object will create a submit button for the form. There's one problem with this form though. If you inspect the HTML that is generated, by viewing the source of the page, you will see that the +action+ attribute for the form is pointing at +/posts/new+. This is a problem because this route goes to the very page that you're on right at the moment, and that route should only be used to display the form for a new post. The form needs to use a different URL in order to go somewhere else. This can be done quite simply with the +:url+ option of +form_for+. Typically in Rails, the action that is used for new form submissions like this is called "create", and so the form should be pointed to that action. Edit the +form_for+ line inside +app/views/posts/new.html.erb+ to look like this: <%= form_for :post, :url => { :action => :create } do |f| %> In this example, a +Hash+ object is passed to the +:url+ option. What Rails will do with this is that it will point the form to the +create+ action of the current controller, the +PostsController+, and will send a +POST+ request to that route. For this to work, you will need to add a route to +config/routes.rb+, right underneath the one for "posts/new": post "posts/create" By using the +post+ method rather than the +get+ method, Rails will define a route that will only respond to POST methods. The POST method is the typical method used by forms all over the web. With the form and its associated route defined, you will be able to fill in the form and then click the submit button to begin the process of creating a new post, so go ahead and do that. When you submit the form, you should see a familiar error: !images/getting_started/unknown_action_create_for_posts.png(Unknown action create for PostsController)! You now need to create the +create+ action within the +PostsController+ for this to work. h4. Creating posts To make the "Unknown action" go away, you can define a +create+ action within the +PostsController+ class in +app/controllers/posts_controller.rb+, underneath the +new+ action: class PostsController < ApplicationController def new end def create end end If you re-submit the form now, you'll see another familiar error: a template is missing. That's ok, we can ignore that for now. What the +create+ action should be doing is saving our new post to a database. When a form is submitted, the fields of the form are sent to Rails as _parameters_. These parameters can then be referenced inside the controller actions, typically to perform a particular task. To see what these parameters look like, change the +create+ action to this: def create render :text => params[:post].inspect end The +render+ method here is taking a very simple hash with a key of +text+ and value of +params[:post].inspect+. The +params+ method is the object which represents the parameters (or fields) coming in from the form. The +params+ method returns a +HashWithIndifferentAccess+ object, which allows you to access the keys of the hash using either strings or symbols. In this situation, the only parameters that matter are the ones from the form. If you re-submit the form one more time you'll now no longer get the missing template error. Instead, you'll see something that looks like the following: {"title"=>"First post!", "text"=>"This is my first post."} This action is now displaying the parameters for the post that are coming in from the form. However, this isn't really all that helpful. Yes, you can see the parameters but nothing in particular is being done with them. h4. Creating the Post model Models in Rails use a singular name, and their corresponding database tables use a plural name. Rails provides a generator for creating models, which most Rails developers tend to use when creating new models. To create the new model, run this command in your terminal: $ rails generate model Post title:string text:text With that command we told Rails that we want a +Post+ model, together with a _title_ attribute of type string, and a _text_ attribute of type text. Those attributes are automatically added to the +posts+ table in the database and mapped to the +Post+ model. Rails responded by creating a bunch of files. For now, we're only interested in +app/models/post.rb+ and +db/migrate/20120419084633_create_posts.rb+ (your name could be a bit different). The latter is responsible for creating the database structure, which is what we'll look at next. TIP: Active Record is smart enough to automatically map column names to model attributes, which means you don't have to declare attributes inside Rails models, as that will be done automatically by Active Record. h4. Running a Migration As we've just seen, +rails generate model+ created a _database migration_ file inside the +db/migrate+ directory. Migrations are Ruby classes that are designed to make it simple to create and modify database tables. Rails uses rake commands to run migrations, and it's possible to undo a migration after it's been applied to your database. Migration filenames include a timestamp to ensure that they're processed in the order that they were created. If you look in the +db/migrate/20120419084633_create_posts.rb+ file (remember, yours will have a slightly different name), here's what you'll find: class CreatePosts < ActiveRecord::Migration def change create_table :posts do |t| t.string :title t.text :text t.timestamps end end end The above migration creates a method named +change+ which will be called when you run this migration. The action defined in this method is also reversible, which means Rails knows how to reverse the change made by this migration, in case you want to reverse it later. When you run this migration it will create a +posts+ table with one string column and a text column. It also creates two timestamp fields to allow Rails to track post creation and update times. More information about Rails migrations can be found in the "Rails Database Migrations":migrations.html guide. At this point, you can use a rake command to run the migration: $ rake db:migrate Rails will execute this migration command and tell you it created the Posts table. == CreatePosts: migrating ==================================================== -- create_table(:posts) -> 0.0019s == CreatePosts: migrated (0.0020s) =========================================== NOTE. Because you're working in the development environment by default, this command will apply to the database defined in the +development+ section of your +config/database.yml+ file. If you would like to execute migrations in another environment, for instance in production, you must explicitly pass it when invoking the command: +rake db:migrate RAILS_ENV=production+. h4. Saving data in the controller Back in +posts_controller+, we need to change the +create+ action to use the new +Post+ model to save the data in the database. Open that file and change the +create+ action to look like this: def create @post = Post.new(params[:post]) @post.save redirect_to :action => :show, :id => @post.id end Here's what's going on: every Rails model can be initialized with its respective attributes, which are automatically mapped to the respective database columns. In the first line we do just that (remember that +params[:post]+ contains the attributes we're interested in). Then, +@post.save+ is responsible for saving the model in the database. Finally, we redirect the user to the +show+ action, wich we'll define later. TIP: As we'll see later, +@post.save+ returns a boolean indicating wherever the model was saved or not. h4. Showing Posts If you submit the form again now, Rails will complain about not finding the +show+ action. That's not very useful though, so let's add the +show+ action before proceeding. Open +config/routes.rb+ and add the following route: get "posts/:id" => "posts#show" The special syntax +:id+ tells rails that this route expects an +:id+ parameter, which in our case will be the id of the post. Note that this time we had to specify the actual mapping, +posts#show+ because otherwise Rails would not know which action to render. As we did before, we need to add the +show+ action in the +posts_controller+ and its respective view. def show @post = Post.find(params[:id]) end A couple of things to note. We use +Post.find+ to find the post we're interested in. We also use an instance variable (prefixed by +@+) to hold a reference to the post object. We do this because Rails will pass all instance variables to the view. Now, create a new file +app/view/posts/show.html.erb+ with the following content:

Title: <%= @post.title %>

Text: <%= @post.text %>

Finally, if you now go to "http://localhost:3000/posts/new":http://localhost:3000/posts/new you'll be able to create a post. Try it! !images/getting_started/show_action_for_posts.png(Show action for posts)! h4. Listing all posts We still need a way to list all our posts, so let's do that. As usual, we'll need a route, a controller action, and a view: # Add to config/routes.rb get "posts" => "posts#index" # Add to app/controllers/posts_controller.rb def index @posts = Post.all end +app/view/posts/index.html.erb+:

Listing posts

<% @posts.each do |post| %> <% end %>
Title Text
<%= post.title %> <%= post.text %>
h4. Adding links You can now create, show, and list posts. Now let's add some links to navigate through pages. Open +app/views/welcome/index.html.erb+ and modify it as follows:

Hello, Rails!

<%= link_to "My Blog", :controller => "posts" %>
The +link_to+ method is one of Rails' built-in view helpers. It creates a hyperlink based on text to display and where to go - in this case, to the path for posts. Let's add links to the other views as well. # app/views/posts/index.html.erb

Listing posts

<%= link_to 'New post', :action => :new %> <% @posts.each do |post| %> <% end %>
Title Text
<%= post.title %> <%= post.text %> <%= link_to 'Show', :action => :show, :id => post.id %>
# app/views/posts/new.html.erb <%= form_for :post do |f| %> ... <% end %> <%= link_to 'Back', :action => :index %> # app/views/posts/show.html.erb

Title: <%= @post.title %>

Text: <%= @post.text %>

<%= link_to 'Back', :action => :index %>
TIP: If you want to link to an action in the same controller, you don't need to specify the +:controller+ option, as Rails will use the current controller by default. TIP: In development mode (which is what you're working in by default), Rails reloads your application with every browser request, so there's no need to stop and restart the web server when a change is made. h4. Adding Some Validation The model file, +app/models/post.rb+ is about as simple as it can get: class Post < ActiveRecord::Base end There isn't much to this file - but note that the +Post+ class inherits from +ActiveRecord::Base+. Active Record supplies a great deal of functionality to your Rails models for free, including basic database CRUD (Create, Read, Update, Destroy) operations, data validation, as well as sophisticated search support and the ability to relate multiple models to one another. Rails includes methods to help you validate the data that you send to models. Open the +app/models/post.rb+ file and edit it: class Post < ActiveRecord::Base validates :title, :presence => true, :length => { :minimum => 5 } end These changes will ensure that all posts have a title that is at least five characters long. Rails can validate a variety of conditions in a model, including the presence or uniqueness of columns, their format, and the existence of associated objects. Validations are covered in detail in "Active Record Validations and Callbacks":active_record_validations_callbacks.html#validations-overview If you open +posts_controller+ again, you'll notice that we don't check the result of calling +@post.save+. We need to change its behavior to show the form back to the user if any error occur: def new @post = Post.new end def create @post = Post.new(params[:post]) if @post.save redirect_to :action => :show, :id => @post.id else render 'new' end end Notice that I've also added +@post = Post.new+ to the +new+ action. I'll explain why I did that in the next section, for now add that to your controller as well. Also notice that we use +render+ instead of +redirect_to+ when +save+ returns false. We can use +render+ so that the +@post+ object is passed back to the view. If you reload "http://localhost:3000/posts/new":http://localhost:3000/posts/new and try to save a post without a title, Rails will send you back to the form, but that's not very useful. You need to tell the user that something went wrong. To do that, you'll modify +app/views/posts/new.html.erb+ to check for error messages: <%= form_for :post, :url => { :action => :create } do |f| %> <% if @post.errors.any? %>

<%= pluralize(@post.errors.count, "error") %> prohibited this post from being saved:

<% end %>

<%= f.label :title %>
<%= f.text_field :title %>

<%= f.label :text %>
<%= f.text_area :text %>

<%= f.submit %>

<% end %> <%= link_to 'Back', :action => :index %>
A few things are going on. We check if there are any errors with +@post.errors.any?+, and in that case we show a list of all errors with +@post.errors.full_messages+. +pluralize+ is a rails helper that takes a number and a string as its arguments. If the number is greater than one, the string will be automatically pluralized. The reason why we added +@post = Post.new+ in +posts_controller+ is that otherwise +@post+ would be +nil+ in our view, and calling +@post.errors.any?+ would throw an error. TIP: Rails automatically wraps fields that contain an error with a div with class +field_with_errors+. You can define a css rule to make them standout. Now you'll get a nice error message when saving a post without title: !images/getting_started/form_with_errors.png(Form With Errors)! h4. Updating Posts We've covered the "CR" part of CRUD. Now let's focus on the "U" part, updating posts. The first step we'll take is adding a +edit+ action to +posts_controller+. Start by adding a route to +config/routes.rb+: get "posts/:id/edit" => "posts#edit" And then add the controller action: def edit @post = Post.find(params[:id]) end The view will contain a form similar to the one we used when creating new posts. Create a file called +app/views/posts/edit.html.erb+ and make it look as follows:

Editing post

<%= form_for :post, :url => { :action => :update, :id => @post.id }, :method => :put do |f| %> <% if @post.errors.any? %>

<%= pluralize(@post.errors.count, "error") %> prohibited this post from being saved:

<% end %>

<%= f.label :title %>
<%= f.text_field :title %>

<%= f.label :text %>
<%= f.text_area :text %>

<%= f.submit %>

<% end %> <%= link_to 'Back', :action => :index %>
This time we point the form to the +update+ action (not defined yet). The +:method => :put+ option tells Rails that we want this form to be submitted via +put+, which is the http method you're expected to use to *update* resources according to the REST protocol. TIP: By default forms built with the +form_for_ helper are sent via +POST+. Moving on, we need to add the +update+ action. The file +config/routes.rb+ will need just one more line: put "posts/:id" => "posts#update" And the +update+ action in +posts_controller+ itself should not look too complicated by now: def update @post = Post.find(params[:id]) if @post.update_attributes(params[:post]) redirect_to :action => :show, :id => @post.id else render 'edit' end end The new method +update_attributes+ is used when you want to update a record that already exists, and it accepts an hash containing the attributes that you want to update. As before, if there was an error updating the post we want to show the form back to the user. TIP: you don't need to pass all attributes to +update_attributes+. For example, if you'd call +@post.update_attributes(:title => 'A new title')+ Rails would only update the +title+ attribute, leaving all other attributes untouched. Finally, we want to show a link to the +edit+ action in the +index+ and +show+ views: # app/view/posts/index.html.erb <% @posts.each do |post| %> <% end %>
Title Text
<%= post.title %> <%= post.text %> <%= link_to 'Show', :action => :show, :id => post.id %> <%= link_to 'Edit', :action => :edit, :id => post.id %>
# app/view/posts/show.html.erb ... <%= link_to 'Back', :action => :index %> | <%= link_to 'Edit', :action => :edit, :id => @post.id %>
And here's how our app looks so far: !images/getting_started/index_action_with_edit_link.png(Index action with edit link)! h4. Using partials to clean up duplication in views +partials+ are what Rails uses to remove duplication in views. Here's a simple example: # app/views/user/show.html.erb

<%= @user.name %>

<%= render 'user_details' %> # app/views/user/_user_details.html.erb <%= @user.location %> <%= @user.about_me %>
The +show+ view will automatically include the content of the +_user_details+ view. Note that partials are prefixed by an underscore, as to not be confused with regular views. However, you don't include the underscore when including them with the +helper+ method. TIP: You can read more about partials in the "Layouts and Rendering in Rails":layouts_and_rendering.html guide. Our +edit+ action looks very similar to the +new+ action, in fact they both share the same code for displaying the form. Lets clean them up by using a +_form+ partial. Create a new file +app/views/posts/_form.html.erb+ with the following content: <%= form_for @post do |f| %> <% if @post.errors.any? %>

<%= pluralize(@post.errors.count, "error") %> prohibited this post from being saved:

<% end %>

<%= f.label :title %>
<%= f.text_field :title %>

<%= f.label :text %>
<%= f.text_area :text %>

<%= f.submit %>

<% end %>
Everything except for the +form_for+ declaration remained the same. I'll explain later how +form_for+ can figure out the right +action+ and +method+ attributes when building the form, for now let's update the +new+ and +edit+ views: # app/views/posts/new.html.erb

New post

<%= render 'form' %> <%= link_to 'Back', :action => :index %> # app/views/posts/edit.html.erb

Edit post

<%= render 'form' %> <%= link_to 'Back', :action => :index %>
Point your browser to "http://localhost:3000/posts/new":http://localhost:3000/posts/new and try creating a new post. Everything still works. Now try editing the post and you'll receive the following error: !images/getting_started/undefined_method_post_path.png(Undefined method post_path)! To understand this error, you need to understand how +form_for+ works. When you pass an object to +form_for+ and you don't specify a +:url+ option, Rails will try to guess the +action+ and +method+ options by checking if the passed object is a new record or not. Rails follows the REST convention, so to create a new +Post+ object it will look for a route named +posts_path+, and to update a +Post+ object it will look for a route named +post_path+ and pass the current object. Similarly, rails knows that it should create new objects via POST and update them via PUT. If you run +rake routes+ from the console you'll see that we already have a +posts_path+ route, which was created automatically by Rails. However, we don't have a +post_path+ yet, which is the reason why we received an error before. # rake routes posts GET /posts(.:format) posts#index posts_new GET /posts/new(.:format) posts#new posts_create POST /posts/create(.:format) posts#create GET /posts/:id(.:format) posts#show GET /posts/:id/edit(.:format) posts#edit PUT /posts/:id(.:format) posts#update root / welcome#index To fix this, open +config/routes.rb+ and modify the +get "posts/:id"+ line like this: get "posts/:id" => "posts#show", :as => :post Now you'll be able to update posts again. h4. Deleting Posts We're now ready to cover the "D" part of CRUD, deleting posts from the database. Following the REST convention, we're going to add a route for deleting posts: # config/routes.rb delete "posts/:id" => "posts#destroy" We use the +delete+ method for destroying resources, which is mapped to the +destroy+ action, which is provided below: # app/controllers/posts_controller.rb def destroy @post = Post.find(params[:id]) @post.destroy redirect_to :action => :index end You can call +destroy+ on Active Record objects when you want to delete them from the dabase. Note that we don't need to add a view for this action since we're redirecting to the +index+ action. Finally, add a 'destroy' link to your +index+ action to wrap everything together. <% @posts.each do |post| %> <% end %>
Title Text
<%= post.title %> <%= post.text %> <%= link_to 'Show', :action => :show, :id => post.id %> <%= link_to 'Edit', :action => :edit, :id => post.id %> <%= link_to 'Destroy', { :action => :destroy, :id => post.id }, :method => :delete, :confirm => 'Are you sure?' %>
Here we're using +link_to+ in a different way. We wrap the +:action+ and +:id+ attributes in a hash so that we can pass other arguments to +link_to+. The +:method+ and +:confirm+ options are used as html5 attributes so that when the click is linked, Rails will first show a confirm dialog to the user, and then submit the link with method +delete+. This is done via javascript automatically. !images/getting_started/confirm_dialog.png(Confirm Dialog)! Congratulations, you can now create, show, list, update and destroy posts. In the next section will see how Rails can aid us when creating REST applications, and how we can refactor our Blog app to take advantage of it. h4. Going Deeper into REST We've now covered all the CRUD actions of a REST app. We did so by declaring separate routes with the appropriate verbs into +config/routes.rb+. Here's how that file looks so far: get "posts" => "posts#index" get "posts/new" post "posts/create" get "posts/:id" => "posts#show", :as => :post get "posts/:id/edit" => "posts#edit" put "posts/:id" => "posts#update" delete "posts/:id" => "posts#destroy" That's a lot to type for covering a single *resource*. Fortunately, Rails provides a +resources+ method which can be used to declare a standard REST resource. Here's how +config/routes/rb+ looks after the cleanup: Blog::Application.routes.draw do resources :posts root :to => "welcome#index" end If you run +rake routes+, you'll see that all the routes that we declared before are still available, and the app still works as before. # rake routes posts GET /posts(.:format) posts#index POST /posts(.:format) posts#create new_post GET /posts/new(.:format) posts#new edit_post GET /posts/:id/edit(.:format) posts#edit post GET /posts/:id(.:format) posts#show PUT /posts/:id(.:format) posts#update DELETE /posts/:id(.:format) posts#destroy root / welcome#index TIP: In general, Rails encourages the use of resources objects in place of declaring routes manually. For more information about routing, see "Rails Routing from the Outside In":routing.html. h3. Adding a Second Model It's time to add a second model to the application. The second model will handle comments on blog posts. h4. Generating a Model We're going to se the same generator that we used before when creating the +Post+ model. This time we'll create a +Comment+ model to hold reference of post comments. Run this command in your terminal: $ rails generate model Comment commenter:string body:text post:references This command will generate four files: |_.File |_.Purpose| |db/migrate/20100207235629_create_comments.rb | Migration to create the comments table in your database (your name will include a different timestamp) | | app/models/comment.rb | The Comment model | | test/unit/comment_test.rb | Unit testing harness for the comments model | | test/fixtures/comments.yml | Sample comments for use in testing | First, take a look at +comment.rb+: class Comment < ActiveRecord::Base belongs_to :post end This is very similar to the +post.rb+ model that you saw earlier. The difference is the line +belongs_to :post+, which sets up an Active Record _association_. You'll learn a little about associations in the next section of this guide. In addition to the model, Rails has also made a migration to create the corresponding database table: class CreateComments < ActiveRecord::Migration def change create_table :comments do |t| t.string :commenter t.text :body t.references :post t.timestamps end add_index :comments, :post_id end end The +t.references+ line sets up a foreign key column for the association between the two models. And the +add_index+ line sets up an index for this association column. Go ahead and run the migration: $ rake db:migrate Rails is smart enough to only execute the migrations that have not already been run against the current database, so in this case you will just see: == CreateComments: migrating ================================================= -- create_table(:comments) -> 0.0008s -- add_index(:comments, :post_id) -> 0.0003s == CreateComments: migrated (0.0012s) ======================================== h4. Associating Models Active Record associations let you easily declare the relationship between two models. In the case of comments and posts, you could write out the relationships this way: * Each comment belongs to one post. * One post can have many comments. In fact, this is very close to the syntax that Rails uses to declare this association. You've already seen the line of code inside the Comment model that makes each comment belong to a Post: class Comment < ActiveRecord::Base belongs_to :post end You'll need to edit the +post.rb+ file to add the other side of the association: class Post < ActiveRecord::Base validates :title, :presence => true, :length => { :minimum => 5 } has_many :comments end These two declarations enable a good bit of automatic behavior. For example, if you have an instance variable +@post+ containing a post, you can retrieve all the comments belonging to that post as an array using +@post.comments+. TIP: For more information on Active Record associations, see the "Active Record Associations":association_basics.html guide. h4. Adding a Route for Comments As with the +welcome+ controller, we will need to add a route so that Rails knows where we would like to navigate to see +comments+. Open up the +config/routes.rb+ file again, and edit it as follows: resources :posts do resources :comments end This creates +comments+ as a _nested resource_ within +posts+. This is another part of capturing the hierarchical relationship that exists between posts and comments. TIP: For more information on routing, see the "Rails Routing from the Outside In":routing.html guide. h4. Generating a Controller With the model in hand, you can turn your attention to creating a matching controller. Again, we'll use the same generator we used before: $ rails generate controller Comments This creates six files and one empty directory: |_.File/Directory |_.Purpose | | app/controllers/comments_controller.rb | The Comments controller | | app/views/comments/ | Views of the controller are stored here | | test/functional/comments_controller_test.rb | The functional tests for the controller | | app/helpers/comments_helper.rb | A view helper file | | test/unit/helpers/comments_helper_test.rb | The unit tests for the helper | | app/assets/javascripts/comment.js.coffee | CoffeeScript for the controller | | app/assets/stylesheets/comment.css.scss | Cascading style sheet for the controller | Like with any blog, our readers will create their comments directly after reading the post, and once they have added their comment, will be sent back to the post show page to see their comment now listed. Due to this, our +CommentsController+ is there to provide a method to create comments and delete spam comments when they arrive. So first, we'll wire up the Post show template (+/app/views/posts/show.html.erb+) to let us make a new comment:

Title: <%= @post.title %>

Text: <%= @post.texthttp://beginningruby.org/ %>

Add a comment:

<%= form_for([@post, @post.comments.build]) do |f| %>

<%= f.label :commenter %>
<%= f.text_field :commenter %>

<%= f.label :body %>
<%= f.text_area :body %>

<%= f.submit %>

<% end %> <%= link_to 'Edit Post', edit_post_path(@post) %> | <%= link_to 'Back to Posts', posts_path %>
This adds a form on the +Post+ show page that creates a new comment by calling the +CommentsController+ +create+ action. Let's wire that up: class CommentsController < ApplicationController def create @post = Post.find(params[:post_id]) @comment = @post.comments.create(params[:comment]) redirect_to post_path(@post) end end You'll see a bit more complexity here than you did in the controller for posts. That's a side-effect of the nesting that you've set up. Each request for a comment has to keep track of the post to which the comment is attached, thus the initial call to the +find+ method of the +Post+ model to get the post in question. In addition, the code takes advantage of some of the methods available for an association. We use the +create+ method on +@post.comments+ to create and save the comment. This will automatically link the comment so that it belongs to that particular post. Once we have made the new comment, we send the user back to the original post using the +post_path(@post)+ helper. As we have already seen, this calls the +show+ action of the +PostsController+ which in turn renders the +show.html.erb+ template. This is where we want the comment to show, so let's add that to the +app/views/posts/show.html.erb+.

Title: <%= @post.title %>

Text: <%= @post.texthttp://beginningruby.org/ %>

Comments

<% @post.comments.each do |comment| %>

Commenter: <%= comment.commenter %>

Comment: <%= comment.body %>

<% end %>

Add a comment:

<%= form_for([@post, @post.comments.build]) do |f| %>

<%= f.label :commenter %>
<%= f.text_field :commenter %>

<%= f.label :body %>
<%= f.text_area :body %>

<%= f.submit %>

<% end %> <%= link_to 'Edit Post', edit_post_path(@post) %> | <%= link_to 'Back to Posts', posts_path %>
Now you can add posts and comments to your blog and have them show up in the right places. !images/getting_started/post_with_comments.png(Post with Comments)! h3. Refactoring Now that we have posts and comments working, take a look at the +app/views/posts/show.html.erb+ template. It is getting long and awkward. We can use partials to clean it up. h4. Rendering Partial Collections First we will make a comment partial to extract showing all the comments for the post. Create the file +app/views/comments/_comment.html.erb+ and put the following into it:

Commenter: <%= comment.commenter %>

Comment: <%= comment.body %>

Then you can change +app/views/posts/show.html.erb+ to look like the following:

Title: <%= @post.title %>

Text: <%= @post.texthttp://beginningruby.org/ %>

Comments

<%= render @post.comments %>

Add a comment:

<%= form_for([@post, @post.comments.build]) do |f| %>

<%= f.label :commenter %>
<%= f.text_field :commenter %>

<%= f.label :body %>
<%= f.text_area :body %>

<%= f.submit %>

<% end %> <%= link_to 'Edit Post', edit_post_path(@post) %> | <%= link_to 'Back to Posts', posts_path %>
This will now render the partial in +app/views/comments/_comment.html.erb+ once for each comment that is in the +@post.comments+ collection. As the +render+ method iterates over the @post.comments collection, it assigns each comment to a local variable named the same as the partial, in this case +comment+ which is then available in the partial for us to show. h4. Rendering a Partial Form Let us also move that new comment section out to its own partial. Again, you create a file +app/views/comments/_form.html.erb+ containing: <%= form_for([@post, @post.comments.build]) do |f| %>

<%= f.label :commenter %>
<%= f.text_field :commenter %>

<%= f.label :body %>
<%= f.text_area :body %>

<%= f.submit %>

<% end %>
Then you make the +app/views/posts/show.html.erb+ look like the following:

Title: <%= @post.title %>

Text: <%= @post.texthttp://beginningruby.org/ %>

Add a comment:

<%= render "comments/form" %> <%= link_to 'Edit Post', edit_post_path(@post) %> | <%= link_to 'Back to Posts', posts_path %>
The second render just defines the partial template we want to render, comments/form. Rails is smart enough to spot the forward slash in that string and realize that you want to render the _form.html.erb file in the app/views/comments directory. The +@post+ object is available to any partials rendered in the view because we defined it as an instance variable. h3. Deleting Comments Another important feature of a blog is being able to delete spam comments. To do this, we need to implement a link of some sort in the view and a +DELETE+ action in the +CommentsController+. So first, let's add the delete link in the +app/views/comments/_comment.html.erb+ partial:

Commenter: <%= comment.commenter %>

Comment: <%= comment.body %>

<%= link_to 'Destroy Comment', [comment.post, comment], :confirm => 'Are you sure?', :method => :delete %>

Clicking this new "Destroy Comment" link will fire off a DELETE /posts/:id/comments/:id to our +CommentsController+, which can then use this to find the comment we want to delete, so let's add a destroy action to our controller: class CommentsController < ApplicationController def create @post = Post.find(params[:post_id]) @comment = @post.comments.create(params[:comment]) redirect_to post_path(@post) end def destroy @post = Post.find(params[:post_id]) @comment = @post.comments.find(params[:id]) @comment.destroy redirect_to post_path(@post) end end The +destroy+ action will find the post we are looking at, locate the comment within the @post.comments collection, and then remove it from the database and send us back to the show action for the post. h4. Deleting Associated Objects If you delete a post then its associated comments will also need to be deleted. Otherwise they would simply occupy space in the database. Rails allows you to use the +dependent+ option of an association to achieve this. Modify the Post model, +app/models/post.rb+, as follows: class Post < ActiveRecord::Base validates :title, :presence => true, :length => { :minimum => 5 } has_many :comments, :dependent => :destroy end h3. Security If you were to publish your blog online, anybody would be able to add, edit and delete posts or delete comments. Rails provides a very simple HTTP authentication system that will work nicely in this situation. In the +PostsController+ we need to have a way to block access to the various actions if the person is not authenticated, here we can use the Rails http_basic_authenticate_with method, allowing access to the requested action if that method allows it. To use the authentication system, we specify it at the top of our +PostsController+, in this case, we want the user to be authenticated on every action, except for +index+ and +show+, so we write that: class PostsController < ApplicationController http_basic_authenticate_with :name => "dhh", :password => "secret", :except => [:index, :show] def index @posts = Post.all # snipped for brevity We also only want to allow authenticated users to delete comments, so in the +CommentsController+ we write: class CommentsController < ApplicationController http_basic_authenticate_with :name => "dhh", :password => "secret", :only => :destroy def create @post = Post.find(params[:post_id]) # snipped for brevity Now if you try to create a new post, you will be greeted with a basic HTTP Authentication challenge !images/challenge.png(Basic HTTP Authentication Challenge)! h3. What's Next? Now that you've seen your first Rails application, you should feel free to update it and experiment on your own. But you don't have to do everything without help. As you need assistance getting up and running with Rails, feel free to consult these support resources: * The "Ruby on Rails guides":index.html * The "Ruby on Rails Tutorial":http://railstutorial.org/book * The "Ruby on Rails mailing list":http://groups.google.com/group/rubyonrails-talk * The "#rubyonrails":irc://irc.freenode.net/#rubyonrails channel on irc.freenode.net Rails also comes with built-in help that you can generate using the rake command-line utility: * Running +rake doc:guides+ will put a full copy of the Rails Guides in the +doc/guides+ folder of your application. Open +doc/guides/index.html+ in your web browser to explore the Guides. * Running +rake doc:rails+ will put a full copy of the API documentation for Rails in the +doc/api+ folder of your application. Open +doc/api/index.html+ in your web browser to explore the API documentation. h3. Configuration Gotchas The easiest way to work with Rails is to store all external data as UTF-8. If you don't, Ruby libraries and Rails will often be able to convert your native data into UTF-8, but this doesn't always work reliably, so you're better off ensuring that all external data is UTF-8. If you have made a mistake in this area, the most common symptom is a black diamond with a question mark inside appearing in the browser. Another common symptom is characters like "ü" appearing instead of "ü". Rails takes a number of internal steps to mitigate common causes of these problems that can be automatically detected and corrected. However, if you have external data that is not stored as UTF-8, it can occasionally result in these kinds of issues that cannot be automatically detected by Rails and corrected. Two very common sources of data that are not UTF-8: * Your text editor: Most text editors (such as Textmate), default to saving files as UTF-8. If your text editor does not, this can result in special characters that you enter in your templates (such as é) to appear as a diamond with a question mark inside in the browser. This also applies to your I18N translation files. Most editors that do not already default to UTF-8 (such as some versions of Dreamweaver) offer a way to change the default to UTF-8. Do so. * Your database. Rails defaults to converting data from your database into UTF-8 at the boundary. However, if your database is not using UTF-8 internally, it may not be able to store all characters that your users enter. For instance, if your database is using Latin-1 internally, and your user enters a Russian, Hebrew, or Japanese character, the data will be lost forever once it enters the database. If possible, use UTF-8 as the internal storage of your database.