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:
```bash
$ 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:
```bash
$ cd blog
```
The `rails new blog` command we ran above created a folder in your
working directory called `blog`. The `blog` directory has a number of
auto-generated files and folders that make up the structure of a Rails
application. Most of the work in this tutorial will happen in the `app/` folder, but here's a basic rundown on the function of each of the files and folders that Rails created by default:
| File/Folder | Purpose |
| ----------- | ------- |
|app/|Contains the controllers, models, views, helpers, mailers and assets for your application. You'll focus on this folder for the remainder of this guide.|
|config/|Configure your application's runtime rules, routes, database, and more. This is covered in more detail in [Configuring Rails Applications](configuring.html)|
|config.ru|Rack configuration for Rack based servers used to start the application.|
|db/|Contains your current database schema, as well as the database migrations.|
|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](http://gembundler.com) |
|lib/|Extended modules for your application.|
|log/|Application log files.|
|public/|The only folder seen to the world as-is. Contains the static files and compiled assets.|
|Rakefile|This file locates and loads tasks that can be run from the command line. The task definitions are defined throughout the components of Rails. Rather than changing Rakefile, you should add your own tasks by adding files to the lib/tasks directory of your application.|
|README.rdoc|This is a brief instruction manual for your application. You should edit this file to tell others what your application does, how to set it up, and so on.|
|test/|Unit tests, fixtures, and other test apparatus. These are covered in [Testing Rails Applications](testing.html)|
|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).|
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.
### 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:
```bash
$ rails server
```
TIP: Compiling CoffeeScript to JavaScript requires a JavaScript runtime and the absence of a runtime will give you an `execjs` error. Usually Mac OS X and Windows come with a JavaScript runtime installed. Rails adds the `therubyracer` gem to Gemfile in a commented line for new apps and you can uncomment if you need it. `therubyrhino` is the recommended runtime for JRuby users and is added by default to Gemfile in apps generated under JRuby. You can investigate about all the supported runtimes at [ExecJS](https://github.com/sstephenson/execjs#readme).
This will fire up WEBrick, a webserver built into Ruby by default. To see your application in action, open a browser window and navigate to <http://localhost:3000>. 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.
### 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:
```bash
$ rails generate controller welcome index
```
Rails will create several files and a route for you.
Most important of these are of course the controller, located at `app/controllers/welcome_controller.rb` and the view, located at `app/views/welcome/index.html.erb`.
Open the `app/views/welcome/index.html.erb` file in your text editor. Delete all of the existing code in the file, and replace it with the following single line of code:
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.
```ruby
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 :to` and uncomment it. It should look something like the following:
```ruby
root to: "welcome#index"
```
The `root to: "welcome#index"` tells Rails to map requests to the root of the application to the welcome controller's index action 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.
TIP: For more information about routing, refer to [Rails Routing from the Outside In](routing.html).
Getting Up and Running
----------------------
Now that you've seen how to create a controller, an action and a view, let's create something with a bit more substance.
In the Blog application, you will now create a new _resource_. A resource is the term used for a collection of similar objects, such as posts, people or animals. You can create, read, update and destroy items for a resource and these operations are referred to as _CRUD_ operations.
In the next section, you will add the ability to create new posts in your application and be able to view them. This is the "C" and the "R" from CRUD: creation and reading. The form for doing this will look like this:
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:
If you open up the newly generated `app/controllers/posts_controller.rb` you'll see a fairly empty controller:
```ruby
class PostsController <ApplicationController
end
```
A controller is simply a class that is defined to inherit from `ApplicationController`. It's inside this class that you'll define methods that will become the actions for this controller. These actions will perform CRUD operations on the posts within our system.
If you refresh <http://localhost:3000/posts/new> 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:
```ruby
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:
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:
```html
<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.
### The first form
To create a form within this template, you will use a <em>form
builder</em>. 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`:
```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:
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.
### 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:
```ruby
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:
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:
```ruby
{"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.
### 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:
```bash
$ 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.
### 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:
```ruby
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](migrations.html).
At this point, you can use a rake command to run the migration:
```bash
$ rake db:migrate
```
Rails will execute this migration command and tell you it created the Posts
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](http://weblog.rubyonrails.org/2012/3/21/strong-parameters/).
And an action for that route inside the `PostsController` in the `app/controllers/posts_controller.rb` file:
```ruby
def index
@posts = Post.all
end
```
And then finally a view for this action, located at `app/views/posts/index.html.erb`:
```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.
### 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:
```html+erb
<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:
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:
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:
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:
| 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 |
Now that you've seen your first Rails application, you should feel free to
update it and experiment on your own. But you don't have to do everything
without help. As you need assistance getting up and running with Rails, feel
free to consult these support resources:
* The [Ruby on Rails guides](index.html)
* The [Ruby on Rails Tutorial](http://railstutorial.org/book)
* The [Ruby on Rails mailing list](http://groups.google.com/group/rubyonrails-talk)
* The [#rubyonrails](irc://irc.freenode.net/#rubyonrails) channel on irc.freenode.net
Rails also comes with built-in help that you can generate using the rake command-line utility:
* Running `rake doc:guides` will put a full copy of the Rails Guides in the `doc/guides` folder of your application. Open `doc/guides/index.html` in your web browser to explore the Guides.
* Running `rake doc:rails` will put a full copy of the API documentation for Rails in the `doc/api` folder of your application. Open `doc/api/index.html` in your web browser to explore the API documentation.
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.
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:
