This guide covers getting up and running with Ruby on Rails.
After reading this guide, you will know:
How to install Rails, create a new Rails application, and connect 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.
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:
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.
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.
TIP: 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>
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
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, 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.
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
.
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.| |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<br />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).|
To begin with, let's get some text up on screen quickly. To do this, you need to get your Rails application server running.
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
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.
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 localhost:3000. You should see the Rails default information page:
TIP: 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.
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>
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, 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 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 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.
TIP: For more information about routing, refer to Rails Routing from the Outside In.
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.
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 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.
NOTE: 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 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 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 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.
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.
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.
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.
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.
TIP: 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) ===========================================
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
.
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.
TIP: As we'll see later, @post.save
returns a boolean
indicating whether the model was saved or not.
If you now go to 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.
TIP: 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.
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 localhost:3000/posts/new and give it a try!
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.
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 %>
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.
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
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 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.
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 when you attempt to do just that on the new post form (http://localhost:3000/posts/new).
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.
TIP: 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.
TIP: 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:
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.
TIP: 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 %>
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.
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.
It's time to add a second model to the application. The second model will handle comments on posts.
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) ========================================
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
.
TIP: For more information on Active Record associations, see the Active Record Associations guide.
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 guide.
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.
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.
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.
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.
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.
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
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
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 #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.
TIP: 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.
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.