1 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 language version 1.9.3 or newer
- The RubyGems packaging system
- To learn more about RubyGems, please read the RubyGems User Guide
- A working installation of the SQLite3 Database
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:
2 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 the "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.
3 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.
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.
The examples below use #
and $
to denote superuser and regular
user terminal prompts respectively in a UNIX-like OS. If you are using
Windows, your prompt will look something like c:\source_code>
3.1 Installing Rails
Open up a command line prompt. On Mac OS X open Terminal.app, on Windows choose
"Run" from your Start menu and type 'cmd.exe'. Any commands prefaced with a
dollar sign $
should be run in the command line. Verify that you have a
current version of Ruby installed:
$ ruby -v ruby 1.9.3p385
To install Rails, use the gem install
command provided by RubyGems:
$ gem install rails
A number of tools exist to help you quickly install Ruby and Ruby on Rails on your system. Windows users can use Rails Installer, while Mac OS X users can use Rails One Click.
To verify that you have everything installed correctly, you should be able to run the following:
$ rails --version
If it says something like "Rails 4.0.0", you are ready to continue.
3.2 Creating the Blog Application
Rails comes with a number of scripts called generators that are designed to make your development life easier by creating everything that's necessary to start working on a particular task. One of these is the new application generator, which will provide you with the foundation of a fresh 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 and install the gem dependencies that are already mentioned in Gemfile
using bundle install
.
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. |
bin/ | Contains the rails script that starts your app and can contain other scripts you use to deploy or run your application. |
config/ | Configure your application's runtime rules, routes, database, and more. This is covered in more detail in Configuring Rails Applications |
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. |
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 |
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. |
test/ | Unit tests, fixtures, and other test apparatus. These are covered in Testing Rails Applications |
tmp/ | Temporary files (like cache, pid and session 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). |
4 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.
4.1 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 the following in the root directory of your rails application:
$ rails server
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.
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. You should see the Rails default information page:
To stop the web server, hit Ctrl+C in the terminal window where it's running. To verify the server has stopped you should see your command prompt cursor again. For most UNIX-like systems including Mac OS X this will be a dollar sign $
. 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.
4.2 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 and a route for you.
create app/controllers/welcome_controller.rb route get "welcome/index" invoke erb create app/views/welcome create app/views/welcome/index.html.erb invoke test_unit create test/controllers/welcome_controller_test.rb invoke helper create app/helpers/welcome_helper.rb invoke test_unit create test/helpers/welcome_helper_test.rb invoke assets invoke coffee create app/assets/javascripts/welcome.js.coffee invoke scss create app/assets/stylesheets/welcome.css.scss
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. Delete all of the existing code in the file, and replace it with the following single line of code:
<h1>Hello, Rails!</h1>
4.3 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. At the moment, "Welcome Aboard" is occupying that spot.
Next, you have to tell Rails where your actual home page is located.
Open the file config/routes.rb
in your editor.
Blog::Application.routes.draw do get "welcome/index" # The priority is based upon order of creation: # first created -> highest priority. # ... # You can have the root of your site routed with "root" # root to: "welcome#index"
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
and uncomment it. It should look something like the following:
root "welcome#index"
The root "welcome#index"
tells Rails to map requests to the root of the application to the welcome controller's index action and get "welcome/index"
tells Rails to map requests to http://localhost:3000/welcome/index 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 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.
For more information about routing, refer to Rails Routing from the Outside In.
5 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.
Rails provides a resources
method which can be used to declare a
standard REST resource. Here's how config/routes.rb
will look like.
Blog::Application.routes.draw do resources :posts root to: "welcome#index" end
If you run rake routes
, you'll see that all the routes for the
standard RESTful actions.
$ 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 PATCH /posts/:id(.:format) posts#update PUT /posts/:id(.:format) posts#update DELETE /posts/:id(.:format) posts#destroy root / welcome#index
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:
It will look a little basic for now, but that's ok. We'll look at improving the styling for it afterwards.
5.1 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
. With the route already defined, requests can now be made to /posts/new
in the application. Navigate to http://localhost:3000/posts/new and you'll see a routing error:
This error occurs because the route needs to have a controller defined in order to serve the request. The solution to this particular problem is simple: 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.
There are public
, private
and protected
methods in Ruby
(for more details you can check on Programming Ruby).
But only public
methods can be actions for controllers.
If you refresh http://localhost:3000/posts/new now, you'll get a new error:
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 you'll see another error:
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:
<h1>New Post</h1>
When you refresh 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.
5.2 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| %> <p> <%= f.label :title %><br> <%= f.text_field :title %> </p> <p> <%= f.label :text %><br> <%= f.text_area :text %> </p> <p> <%= f.submit %> </p> <% 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: posts_path do |f| %>
In this example, the posts_path
helper 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.
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:
You now need to create the create
action within the PostsController
for this to work.
5.3 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 an ActiveSupport::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.
5.4 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.
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.
5.5 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.
For more information about migrations, refer to Rails Database Migrations.
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) ===========================================
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
.
5.6 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 app/controllers/posts_controller.rb
and change the create
action to look like this:
def create @post = Post.new(params[:post]) @post.save redirect_to @post 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,
which we'll define later.
As we'll see later, @post.save
returns a boolean indicating
whether the model was saved or not.
If you now go to http://localhost:3000/posts/new you'll almost be able to create a post. Try it! You should get an error that looks like this:
Rails has several security features that help you write secure applications,
and you're running into one of them now. This one is called
strong_parameters
, which requires us to tell Rails exactly which parameters
we want to accept in our controllers. In this case, we want to allow the
title
and text
parameters, so change your create
controller action to
look like this:
def create @post = Post.new(post_params) @post.save redirect_to @post end private def post_params params.require(:post).permit(:title, :text) end
See the permit
? It allows us to accept both title
and text
in this
action.
Note that def post_params
is private. This new approach prevents an attacker from
setting the model's attributes by manipulating the hash passed to the model.
For more information, refer to
this blog post about Strong Parameters.
5.7 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.
As we have seen in the output of rake routes
, the route for show
action is
as follows:
post GET /posts/:id(.:format) 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.
As we did before, we need to add the show
action in
app/controllers/posts_controller.rb
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/views/posts/show.html.erb
with the following
content:
<p> <strong>Title:</strong> <%= @post.title %> </p> <p> <strong>Text:</strong> <%= @post.text %> </p>
With this change, you should finally be able to create new posts. Visit http://localhost:3000/posts/new and give it a try!
5.8 Listing all posts
We still need a way to list all our posts, so let's do that.
We'll use a specific route from config/routes.rb
:
posts GET /posts(.:format) posts#index
And an action for that route inside the PostsController
in the app/controllers/posts_controller.rb
file:
def index @posts = Post.all end
And then finally a view for this action, located at app/views/posts/index.html.erb
:
<h1>Listing posts</h1> <table> <tr> <th>Title</th> <th>Text</th> </tr> <% @posts.each do |post| %> <tr> <td><%= post.title %></td> <td><%= post.text %></td> </tr> <% end %> </table>
Now if you go to http://localhost:3000/posts
you will see a list of all the posts that you have created.
5.9 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:
<h1>Hello, Rails!</h1> <%= 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, starting with adding this "New Post" link to app/views/posts/index.html.erb
, placing it above the <table>
tag:
<%= link_to 'New post', new_post_path %>
This link will allow you to bring up the form that lets you create a new post. You should also add a link to this template — app/views/posts/new.html.erb
— to go back to the index
action. Do this by adding this underneath the form in this template:
<%= form_for :post do |f| %> ... <% end %> <%= link_to 'Back', posts_path %>
Finally, add another link to the app/views/posts/show.html.erb
template to go back to the index
action as well, so that people who are viewing a single post can go back and view the whole list again:
<p> <strong>Title:</strong> <%= @post.title %> </p> <p> <strong>Text:</strong> <%= @post.text %> </p> <%= link_to 'Back', posts_path %>
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.
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.
5.10 Allowing the update of fields
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.
5.11 Adding Some Validation
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
With the validation now in place, when you call @post.save
on an invalid
post, it will return false
. If you open app/controllers/posts_controller.rb
again, you'll notice that we don't check the result of calling @post.save
inside the create
action. If @post.save
fails in this situation, we need to
show the form back to the user. To do this, change the new
and create
actions inside app/controllers/posts_controller.rb
to these:
def new @post = Post.new end def create @post = Post.new(params[:post].permit(:title, :text)) if @post.save redirect_to @post else render 'new' end end
The new
action is now creating a new instance variable called @post
, and
you'll see why that is in just a few moments.
Notice that inside the create
action we use render
instead of redirect_to
when save
returns false
. The render
method is used so that the @post
object is passed back to the new
template when it is rendered. This rendering is done within the same request as the form submission, whereas the redirect_to
will tell the browser to issue another request.
If you reload
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: posts_path do |f| %> <% if @post.errors.any? %> <div id="error_explanation"> <h2><%= pluralize(@post.errors.count, "error") %> prohibited this post from being saved:</h2> <ul> <% @post.errors.full_messages.each do |msg| %> <li><%= msg %></li> <% end %> </ul> </div> <% end %> <p> <%= f.label :title %><br> <%= f.text_field :title %> </p> <p> <%= f.label :text %><br> <%= f.text_area :text %> </p> <p> <%= f.submit %> </p> <% end %> <%= link_to 'Back', posts_path %>
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.
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 when you attempt to do just that on the new post form (http://localhost:3000/posts/new).
5.12 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 an edit
action to posts_controller
.
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:
<h1>Editing post</h1> <%= form_for :post, url: post_path(@post), method: :patch do |f| %> <% if @post.errors.any? %> <div id="error_explanation"> <h2><%= pluralize(@post.errors.count, "error") %> prohibited this post from being saved:</h2> <ul> <% @post.errors.full_messages.each do |msg| %> <li><%= msg %></li> <% end %> </ul> </div> <% end %> <p> <%= f.label :title %><br> <%= f.text_field :title %> </p> <p> <%= f.label :text %><br> <%= f.text_area :text %> </p> <p> <%= f.submit %> </p> <% end %> <%= link_to 'Back', posts_path %>
This time we point the form to the update
action, which is not defined yet
but will be very soon.
The method: :patch
option tells Rails that we want this form to be submitted
via the PATCH
HTTP method which is the HTTP method you're expected to use to
update resources according to the REST protocol.
By default forms built with the form_for helper are sent via POST
.
Next we need to create the update
action in app/controllers/posts_controller.rb
:
def update @post = Post.find(params[:id]) if @post.update(params[:post].permit(:title, :text)) redirect_to @post else render 'edit' end end
The new method, update
, is used when you want to update a record
that already exists, and it accepts a 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.
You don't need to pass all attributes to update
. For
example, if you'd call @post.update(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 list of all the
posts, so let's add that now to app/views/posts/index.html.erb
to make it
appear next to the "Show" link:
<table> <tr> <th>Title</th> <th>Text</th> <th></th> <th></th> </tr> <% @posts.each do |post| %> <tr> <td><%= post.title %></td> <td><%= post.text %></td> <td><%= link_to 'Show', post %></td> <td><%= link_to 'Edit', edit_post_path(post) %></td> </tr> <% end %> </table>
And we'll also add one to the app/views/posts/show.html.erb
template as well,
so that there's also an "Edit" link on a post's page. Add this at the bottom of
the template:
... <%= link_to 'Back', posts_path %> | <%= link_to 'Edit', edit_post_path(@post) %>
And here's how our app looks so far:
5.13 Using partials to clean up duplication in views
Our edit
page looks very similar to the new
page, in fact they
both share the same code for displaying the form. Let's remove some duplication
by using a view partial. By convention, partial files are prefixed by an
underscore.
You can read more about partials in the Layouts and Rendering in Rails guide.
Create a new file app/views/posts/_form.html.erb
with the following
content:
<%= form_for @post do |f| %> <% if @post.errors.any? %> <div id="error_explanation"> <h2><%= pluralize(@post.errors.count, "error") %> prohibited this post from being saved:</h2> <ul> <% @post.errors.full_messages.each do |msg| %> <li><%= msg %></li> <% end %> </ul> </div> <% end %> <p> <%= f.label :title %><br> <%= f.text_field :title %> </p> <p> <%= f.label :text %><br> <%= f.text_area :text %> </p> <p> <%= f.submit %> </p> <% end %>
Everything except for the form_for
declaration remained the same.
How form_for
can figure out the right action
and method
attributes
when building the form will be explained in just a moment. For now, let's update the
app/views/posts/new.html.erb
view to use this new partial, rewriting it
completely:
<h1>New post</h1> <%= render 'form' %> <%= link_to 'Back', posts_path %>
Then do the same for the app/views/posts/edit.html.erb
view:
<h1>Edit post</h1> <%= render 'form' %> <%= link_to 'Back', posts_path %>
5.14 Deleting Posts
We're now ready to cover the "D" part of CRUD, deleting posts from the
database. Following the REST convention, the route for
deleting posts in the config/routes.rb
is:
DELETE /posts/:id(.:format) posts#destroy
The delete
routing method should be used for routes that destroy
resources. If this was left as a typical get
route, it could be possible for
people to craft malicious URLs like this:
<a href='http://example.com/posts/1/destroy'>look at this cat!</a>
We use the delete
method for destroying resources, and this route is mapped to
the destroy
action inside app/controllers/posts_controller.rb
, which doesn't exist yet, but is
provided below:
def destroy @post = Post.find(params[:id]) @post.destroy redirect_to posts_path end
You can call destroy
on Active Record objects when you want to delete
them from the database. 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 template
(app/views/posts/index.html.erb
) to wrap everything
together.
<h1>Listing Posts</h1> <%= link_to 'New post', new_post_path %> <table> <tr> <th>Title</th> <th>Text</th> <th></th> <th></th> <th></th> </tr> <% @posts.each do |post| %> <tr> <td><%= post.title %></td> <td><%= post.text %></td> <td><%= link_to 'Show', post_path(post) %></td> <td><%= link_to 'Edit', edit_post_path(post) %></td> <td><%= link_to 'Destroy', post_path(post), method: :delete, data: { confirm: 'Are you sure?' } %></td> </tr> <% end %> </table>
Here we're using link_to
in a different way. We pass the named route as the first argument,
and then the final two keys as another argument. The :method
and :'data-confirm'
options are used as HTML5 attributes so that when the link is clicked,
Rails will first show a confirm dialog to the user, and then submit the link with method delete
.
This is done via the JavaScript file jquery_ujs
which is automatically included
into your application's layout (app/views/layouts/application.html.erb
) when you
generated the application. Without this file, the confirmation dialog box wouldn't appear.
Congratulations, you can now create, show, list, update and destroy posts.
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.
6 Adding a Second Model
It's time to add a second model to the application. The second model will handle comments on posts.
6.1 Generating a Model
We're going to see 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/models/comment_test.rb | Testing harness for the comments model |
test/fixtures/comments.yml | Sample comments for use in testing |
First, take a look at app/models/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) ========================================
6.2 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 (app/models/comment.rb) that
makes each comment belong to a Post:
class Comment < ActiveRecord::Base belongs_to :post end
You'll need to edit app/models/post.rb
to add the other side of the association:
class Post < ActiveRecord::Base has_many :comments validates :title, presence: true, length: { minimum: 5 } [...] 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
.
For more information on Active Record associations, see the Active Record Associations guide.
6.3 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.
For more information on routing, see the Rails Routing guide.
6.4 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/controllers/comments_controller_test.rb | The test for the controller |
app/helpers/comments_helper.rb | A view helper file |
test/helpers/comments_helper_test.rb | The test 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:
<p> <strong>Title:</strong> <%= @post.title %> </p> <p> <strong>Text:</strong> <%= @post.text %> </p> <h2>Add a comment:</h2> <%= form_for([@post, @post.comments.build]) do |f| %> <p> <%= f.label :commenter %><br /> <%= f.text_field :commenter %> </p> <p> <%= f.label :body %><br /> <%= f.text_area :body %> </p> <p> <%= f.submit %> </p> <% end %> <%= link_to 'Back', posts_path %> | <%= link_to 'Edit', edit_post_path(@post) %>
This adds a form on the Post
show page that creates a new comment by
calling the CommentsController
create
action. The form_for
call here uses
an array, which will build a nested route, such as /posts/1/comments
.
Let's wire up the create
in app/controllers/comments_controller.rb
:
class CommentsController < ApplicationController def create @post = Post.find(params[:post_id]) @comment = @post.comments.create(params[:comment].permit(:commenter, :body)) 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
.
<p> <strong>Title:</strong> <%= @post.title %> </p> <p> <strong>Text:</strong> <%= @post.text %> </p> <h2>Comments</h2> <% @post.comments.each do |comment| %> <p> <strong>Commenter:</strong> <%= comment.commenter %> </p> <p> <strong>Comment:</strong> <%= comment.body %> </p> <% end %> <h2>Add a comment:</h2> <%= form_for([@post, @post.comments.build]) do |f| %> <p> <%= f.label :commenter %><br /> <%= f.text_field :commenter %> </p> <p> <%= f.label :body %><br /> <%= f.text_area :body %> </p> <p> <%= f.submit %> </p> <% 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.
7 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.
7.1 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:
<p> <strong>Commenter:</strong> <%= comment.commenter %> </p> <p> <strong>Comment:</strong> <%= comment.body %> </p>
Then you can change app/views/posts/show.html.erb
to look like the
following:
<p> <strong>Title:</strong> <%= @post.title %> </p> <p> <strong>Text:</strong> <%= @post.text %> </p> <h2>Comments</h2> <%= render @post.comments %> <h2>Add a comment:</h2> <%= form_for([@post, @post.comments.build]) do |f| %> <p> <%= f.label :commenter %><br /> <%= f.text_field :commenter %> </p> <p> <%= f.label :body %><br /> <%= f.text_area :body %> </p> <p> <%= f.submit %> </p> <% 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.
7.2 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| %> <p> <%= f.label :commenter %><br /> <%= f.text_field :commenter %> </p> <p> <%= f.label :body %><br /> <%= f.text_area :body %> </p> <p> <%= f.submit %> </p> <% end %>
Then you make the app/views/posts/show.html.erb
look like the following:
<p> <strong>Title:</strong> <%= @post.title %> </p> <p> <strong>Text:</strong> <%= @post.text %> </p> <h2>Comments</h2> <%= render @post.comments %> <h2>Add a comment:</h2> <%= 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.
8 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:
<p> <strong>Commenter:</strong> <%= comment.commenter %> </p> <p> <strong>Comment:</strong> <%= comment.body %> </p> <p> <%= link_to 'Destroy Comment', [comment.post, comment], method: :delete, data: { confirm: 'Are you sure?' } %> </p>
Clicking this new "Destroy Comment" link will fire off a DELETE
/posts/:post_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 (app/controllers/comments_controller.rb
):
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.
8.1 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 has_many :comments, dependent: :destroy validates :title, presence: true, length: { minimum: 5 } [...] end
9 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 in app/controllers/posts_controller.rb
:
class PostsController < ApplicationController http_basic_authenticate_with name: "dhh", password: "secret", except: [:index, :show] def index @posts = Post.all end # snipped for brevity
We also only want to allow authenticated users to delete comments, so in the
CommentsController
(app/controllers/comments_controller.rb
) we write:
class CommentsController < ApplicationController http_basic_authenticate_with name: "dhh", password: "secret", only: :destroy def create @post = Post.find(params[:post_id]) ... end # snipped for brevity
Now if you try to create a new post, you will be greeted with a basic HTTP Authentication challenge
10 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
- The Ruby on Rails Tutorial
- The Ruby on Rails mailing list
- The #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 thedoc/guides
folder of your application. Opendoc/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 thedoc/api
folder of your application. Opendoc/api/index.html
in your web browser to explore the API documentation.
To be able to generate the Rails Guides locally with the doc:guides
rake task you need to install the RedCloth gem. Add it to your Gemfile
and run bundle install
and you're ready to go.
11 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.
Feedback
You're encouraged to help improve the quality of this guide.
Please contribute if you see any typos or factual errors. To get started, you can read our documentation contributions section.
You may also find incomplete content, or stuff that is not up to date. Please do add any missing documentation for master. Make sure to check Edge Guides first to verify if the issues are already fixed or not on the master branch. Check the Ruby on Rails Guides Guidelines for style and conventions.
If for whatever reason you spot something to fix but cannot patch it yourself, please open an issue.
And last but not least, any kind of discussion regarding Ruby on Rails documentation is very welcome in the rubyonrails-docs mailing list.