Change the username and password in the +development+ section as appropriate.
TIP: You don't have to update the database configurations manually. If you had a look at the options of application generator, you have seen that one of them is named --database. It lets you choose an adapter for couple of most used relational databases. You can even run the generator repeatedly: cd .. && rails new blog --database=mysql. When you confirm the overwriting of the +config/database.yml+ file, your application will be configured for MySQL instead of SQLite.
h4. Creating the Database
Now that you have your database configured, it's time to have Rails create an empty database for you. You can do this by running a rake command:
$ rake db:create
This will create your development and test SQLite3 databases inside the db/ folder.
TIP: Rake is a general-purpose command-runner that Rails uses for many things. You can see the list of available rake commands in your application by running +rake -T+.
h3. Hello, Rails!
One of the traditional places to start with a new language is by getting some text up on screen quickly. To do this, you need to get your Rails application server running.
h4. Starting up the Web Server
You actually have a functional Rails application already. To see it, you need to start a web server on your development machine. You can do this by running:
$ rails server
This will fire up an instance of the WEBrick web server by default (Rails can also use several other web servers). To see your application in action, open a browser window and navigate to "http://localhost:3000":http://localhost:3000. You should see Rails' default information page:
!images/rails_welcome.png(Welcome Aboard screenshot)!
TIP: To stop the web server, hit Ctrl+C in the terminal window where it's running. In development mode, Rails does not generally require you to stop the server; changes you make in files will be automatically picked up by the server.
The "Welcome Aboard" page is the _smoke test_ for a new Rails application: it makes sure that you have your software configured correctly enough to serve a page. You can also click on the _About your application’s environment_ link to see a summary of your application's environment.
h4. Say "Hello", Rails
To get Rails saying "Hello", you need to create at minimum a controller and a view. Fortunately, you can do that in a single command. Enter this command in your terminal:
$ rails generate controller home index
TIP: If you're on Windows, or your Ruby is set up in some non-standard fashion, you may need to explicitly pass Rails +rails+ commands to Ruby: ruby \path\to\your\application\script\rails generate controller home index.
Rails will create several files for you, including +app/views/home/index.html.erb+. This is the template that will be used to display the results of the +index+ action (method) in the +home+ controller. Open this file in your text editor and edit it to contain a single line of code:
Hello, Rails!
h4. Setting the Application Home Page
Now that we have made the controller and view, we need to tell Rails when we want "Hello Rails" to show up. In our case, we want it to show up when we navigate to the root URL of our site, "http://localhost:3000":http://localhost:3000, instead of the "Welcome Aboard" smoke test.
The first step to doing this is to delete the default page from your application:
$ rm public/index.html
We need to do this as Rails will deliver any static file in the +public+ directory in preference to any dynamic content we generate from the controllers.
Now, you have to tell Rails where your actual home page is located. Open the file +config/routes.rb+ in your editor. This is your application's _routing file_ which holds entries in a special DSL (domain-specific language) that tells Rails how to connect incoming requests to controllers and actions. This file contains many sample routes on commented lines, and one of them actually shows you how to connect the root of your site to a specific controller and action. Find the line beginning with +root :to+, uncomment it and change it like the following:
Blog::Application.routes.draw do
#...
# You can have the root of your site routed with "root"
# just remember to delete public/index.html.
root :to => "home#index"
The +root :to => "home#index"+ tells Rails to map the root action to the home controller's index action.
Now if you navigate to "http://localhost:3000":http://localhost:3000 in your browser, you'll see +Hello, Rails!+.
NOTE. For more information about routing, refer to "Rails Routing from the Outside In":routing.html.
h3. Getting Up and Running Quickly with Scaffolding
Rails _scaffolding_ is a quick way to generate some of the major pieces of an application. If you want to create the models, views, and controllers for a new resource in a single operation, scaffolding is the tool for the job.
h3. Creating a Resource
In the case of the blog application, you can start by generating a scaffolded Post resource: this will represent a single blog posting. To do this, enter this command in your terminal:
$ rails generate scaffold Post name:string title:string content:text
NOTE. While scaffolding will get you up and running quickly, the code it generates is unlikely to be a perfect fit for your application. You'll most probably want to customize the generated code. Many experienced Rails developers avoid scaffolding entirely, preferring to write all or most of their source code from scratch. Rails, however, makes it really simple to customize templates for generated models, controllers, views and other source files. You'll find more information in the "Creating and Customizing Rails Generators & Templates":generators.html guide.
The scaffold generator will build 15 files in your application, along with some folders, and edit one more. Here's a quick overview of what it creates:
|_.File |_.Purpose|
|db/migrate/20100207214725_create_posts.rb |Migration to create the posts table in your database (your name will include a different timestamp)|
|app/models/post.rb |The Post model|
|test/fixtures/posts.yml |Dummy posts for use in testing|
|app/controllers/posts_controller.rb |The Posts controller|
|app/views/posts/index.html.erb |A view to display an index of all posts |
|app/views/posts/edit.html.erb |A view to edit an existing post|
|app/views/posts/show.html.erb |A view to display a single post|
|app/views/posts/new.html.erb |A view to create a new post|
|app/views/posts/_form.html.erb |A partial to control the overall look and feel of the form used in edit and new views|
|app/helpers/posts_helper.rb |Helper functions to be used from the post views|
|app/assets/stylesheets/scaffold.css.scss |Cascading style sheet to make the scaffolded views look better|
|test/unit/post_test.rb |Unit testing harness for the posts model|
|test/functional/posts_controller_test.rb |Functional testing harness for the posts controller|
|test/unit/helpers/posts_helper_test.rb |Unit testing harness for the posts helper|
|config/routes.rb |Edited to include routing information for posts|
h4. Running a Migration
One of the products of the +rails generate scaffold+ command is a _database migration_. 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/20100207214725_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 :name
t.string :title
t.text :content
t.timestamps
end
end
end
The above migration creates a method name +change+ which will be called when you run this migration. The action defined in that method is also reversible, which means Rails knows how to reverse the change made by this migration, in case you want to reverse it at later date. By default, when you run this migration it will creates a +posts+ table with two string columns and a text column. It also creates two timestamp fields to track record creation and updating. More information about Rails migrations can be found in the "Rails Database Migrations":migrations.html guide.
At this point, you can use a rake command to run the migration:
$ rake db:migrate
Rails will execute this migration command and tell you it created the Posts table.
== CreatePosts: migrating ====================================================
-- create_table(:posts)
-> 0.0019s
== CreatePosts: migrated (0.0020s) ===========================================
NOTE. Because you're working in the development environment by default, this command will apply to the database defined in the +development+ section of your +config/database.yml+ file. If you would like to execute migrations in other environment, for instance in production, you must explicitly pass it when invoking the command: rake db:migrate RAILS_ENV=production.
h4. Adding a Link
To hook the posts up to the home page you've already created, you can add a link to the home page. Open +app/views/home/index.html.erb+ and modify it as follows:
Hello, Rails!
<%= link_to "My Blog", posts_path %>
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.
h4. Working with Posts in the Browser
Now you're ready to start working with posts. To do that, navigate to "http://localhost:3000":http://localhost:3000/ and then click the "My Blog" link:
!images/posts_index.png(Posts Index screenshot)!
This is the result of Rails rendering the +index+ view of your posts. There aren't currently any posts in the database, but if you click the +New Post+ link you can create one. After that, you'll find that you can edit posts, look at their details, or destroy them. All of the logic and HTML to handle this was built by the single +rails generate scaffold+ command.
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.
Congratulations, you're riding the rails! Now it's time to see how it all works.
h4. The Model
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.
h4. 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 :name, :presence => true
validates :title, :presence => true,
:length => { :minimum => 5 }
end
These changes will ensure that all posts have a name and a title, and that the title 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.
h4. Using the Console
To see your validations in action, you can use the console. The console is a command-line tool that lets you execute Ruby code in the context of your application:
$ rails console
TIP: The default console will make changes to your database. You can instead open a console that will roll back any changes you make by using +rails console --sandbox+.
After the console loads, you can use it to work with your application's models:
>> p = Post.new(:content => "A new post")
=> #
>> p.save
=> false
>> p.errors
=> #["can't be blank",
"is too short (minimum is 5 characters)"],
:name=>["can't be blank"] }>
This code shows creating a new +Post+ instance, attempting to save it and getting +false+ for a return value (indicating that the save failed), and inspecting the +errors+ of the post.
When you're finished, type +exit+ and hit +return+ to exit the console.
TIP: Unlike the development web server, the console does not automatically load your code afresh for each line. If you make changes to your models while the console is open, type +reload!+ at the console prompt to load them.
h4. Listing All Posts
The easiest place to start looking at functionality is with the code that lists all posts. Open the file +app/controllers/posts_controller.rb+ and look at the +index+ action:
def index
@posts = Post.all
respond_to do |format|
format.html # index.html.erb
format.json { render :json => @posts }
end
end
+Post.all+ calls the +Post+ model to return all of the posts currently in the database. The result of this call is an array of posts that we store in an instance variable called +@posts+.
TIP: For more information on finding records with Active Record, see "Active Record Query Interface":active_record_querying.html.
The +respond_to+ block handles both HTML and JSON calls to this action. If you browse to "http://localhost:3000/posts.json":http://localhost:3000/posts.json, you'll see a JSON containing all of the posts. The HTML format looks for a view in +app/views/posts/+ with a name that corresponds to the action name. Rails makes all of the instance variables from the action available to the view. Here's +app/views/posts/index.html.erb+:
Listing posts
| Name |
Title |
Content |
|
|
|
<% @posts.each do |post| %>
| <%= post.name %> |
<%= post.title %> |
<%= post.content %> |
<%= link_to 'Show', post %> |
<%= link_to 'Edit', edit_post_path(post) %> |
<%= link_to 'Destroy', post, :confirm => 'Are you sure?', :method => :delete %> |
<% end %>
<%= link_to 'New post', new_post_path %>
This view iterates over the contents of the +@posts+ array to display content and links. A few things to note in the view:
* +link_to+ builds a hyperlink to a particular destination
* +edit_post_path+ and +new_post_path+ are helpers that Rails provides as part of RESTful routing. You'll see a variety of these helpers for the different actions that the controller includes.
NOTE. In previous versions of Rails, you had to use +<%=h post.name %>+ so that any HTML would be escaped before being inserted into the page. In Rails 3.0, this is now the default. To get unescaped HTML, you now use +<%= raw post.name %>+.
TIP: For more details on the rendering process, see "Layouts and Rendering in Rails":layouts_and_rendering.html.
h4. Customizing the Layout
The view is only part of the story of how HTML is displayed in your web browser. Rails also has the concept of +layouts+, which are containers for views. When Rails renders a view to the browser, it does so by putting the view's HTML into a layout's HTML. In previous versions of Rails, the +rails generate scaffold+ command would automatically create a controller specific layout, like +app/views/layouts/posts.html.erb+, for the posts controller. However this has been changed in Rails 3.0. An application specific +layout+ is used for all the controllers and can be found in +app/views/layouts/application.html.erb+. Open this layout in your editor and modify the +body+ tag:
Blog
<%= stylesheet_link_tag :all %>
<%= javascript_include_tag :defaults %>
<%= csrf_meta_tags %>
<%= yield %>
Now when you refresh the +/posts+ page, you'll see a gray background to the page. This same gray background will be used throughout all the views for posts.
h4. Creating New Posts
Creating a new post involves two actions. The first is the +new+ action, which instantiates an empty +Post+ object:
def new
@post = Post.new
respond_to do |format|
format.html # new.html.erb
format.json { render :json => @post }
end
end
The +new.html.erb+ view displays this empty Post to the user:
New post
<%= render 'form' %>
<%= link_to 'Back', posts_path %>
The +<%= render 'form' %>+ line is our first introduction to _partials_ in Rails. A partial is a snippet of HTML and Ruby code that can be reused in multiple locations. In this case, the form used to make a new post, is basically identical to a form used to edit a post, both have text fields for the name and title and a text area for the content with a button to make a new post or update the existing post.
If you take a look at +views/posts/_form.html.erb+ file, you will see the following:
<%= form_for(@post) do |f| %>
<% if @post.errors.any? %>
<%= pluralize(@post.errors.count, "error") %> prohibited this post from being saved:
<% @post.errors.full_messages.each do |msg| %>
- <%= msg %>
<% end %>
<% end %>
<%= f.label :name %>
<%= f.text_field :name %>
<%= f.label :title %>
<%= f.text_field :title %>
<%= f.label :content %>
<%= f.text_area :content %>
<%= f.submit %>
<% end %>
This partial receives all the instance variables defined in the calling view file, so in this case, the controller assigned the new Post object to +@post+ and so, this is available in both the view and partial as +@post+.
For more information on partials, refer to the "Layouts and Rendering in Rails":layouts_and_rendering.html#using-partials guide.
The +form_for+ block is used to create an HTML form. Within this block, you have access to methods to build various controls on the form. For example, +f.text_field :name+ tells Rails to create a text input on the form, and to hook it up to the +name+ attribute of the instance being displayed. You can only use these methods with attributes of the model that the form is based on (in this case +name+, +title+, and +content+). Rails uses +form_for+ in preference to having you write raw HTML because the code is more succinct, and because it explicitly ties the form to a particular model instance.
The +form_for+ block is also smart enough to work out if you are doing a _New Post_ or an _Edit Post_ action, and will set the form +action+ tags and submit button names appropriately in the HTML output.
TIP: If you need to create an HTML form that displays arbitrary fields, not tied to a model, you should use the +form_tag+ method, which provides shortcuts for building forms that are not necessarily tied to a model instance.
When the user clicks the +Create Post+ button on this form, the browser will send information back to the +create+ method of the controller (Rails knows to call the +create+ method because the form is sent with an HTTP POST request; that's one of the conventions that I mentioned earlier):
def create
@post = Post.new(params[:post])
respond_to do |format|
if @post.save
format.html { redirect_to(@post,
:notice => 'Post was successfully created.') }
format.json { render :json => @post,
:status => :created, :location => @post }
else
format.html { render :action => "new" }
format.json { render :json => @post.errors,
:status => :unprocessable_entity }
end
end
end
The +create+ action instantiates a new Post object from the data supplied by the user on the form, which Rails makes available in the +params+ hash. After successfully saving the new post, +create+ returns the appropriate format that the user has requested (HTML in our case). It then redirects the user to the resulting post +show+ action and sets a notice to the user that the Post was successfully created.
If the post was not successfully saved, due to a validation error, then the controller returns the user back to the +new+ action with any error messages so that the user has the chance to fix the error and try again.
The "Post was successfully created." message is stored inside of the Rails +flash+ hash, (usually just called _the flash_) so that messages can be carried over to another action, providing the user with useful information on the status of their request. In the case of +create+, the user never actually sees any page rendered during the Post creation process, because it immediately redirects to the new Post as soon Rails saves the record. The Flash carries over a message to the next action, so that when the user is redirected back to the +show+ action, they are presented with a message saying "Post was successfully created."
h4. Showing an Individual Post
When you click the +show+ link for a post on the index page, it will bring you to a URL like +http://localhost:3000/posts/1+. Rails interprets this as a call to the +show+ action for the resource, and passes in +1+ as the +:id+ parameter. Here's the +show+ action:
def show
@post = Post.find(params[:id])
respond_to do |format|
format.html # show.html.erb
format.json { render :json => @post }
end
end
The +show+ action uses +Post.find+ to search for a single record in the database by its id value. After finding the record, Rails displays it by using +show.html.erb+:
<%= notice %>
Name:
<%= @post.name %>
Title:
<%= @post.title %>
Content:
<%= @post.content %>
<%= link_to 'Edit', edit_post_path(@post) %> |
<%= link_to 'Back', posts_path %>
h4. Editing Posts
Like creating a new post, editing a post is a two-part process. The first step is a request to +edit_post_path(@post)+ with a particular post. This calls the +edit+ action in the controller:
def edit
@post = Post.find(params[:id])
end
After finding the requested post, Rails uses the +edit.html.erb+ view to display it:
Editing post
<%= render 'form' %>
<%= link_to 'Show', @post %> |
<%= link_to 'Back', posts_path %>
Again, as with the +new+ action, the +edit+ action is using the +form+ partial, this time however, the form will do a PUT action to the PostsController and the submit button will display "Update Post"
Submitting the form created by this view will invoke the +update+ action within the controller:
def update
@post = Post.find(params[:id])
respond_to do |format|
if @post.update_attributes(params[:post])
format.html { redirect_to(@post,
:notice => 'Post was successfully updated.') }
format.json { render :json => {}, :status => :ok }
else
format.html { render :action => "edit" }
format.json { render :json => @post.errors,
:status => :unprocessable_entity }
end
end
end
In the +update+ action, Rails first uses the +:id+ parameter passed back from the edit view to locate the database record that's being edited. The +update_attributes+ call then takes the rest of the parameters from the request and applies them to this record. If all goes well, the user is redirected to the post's +show+ view. If there are any problems, it's back to the +edit+ view to correct them.
h4. Destroying a Post
Finally, clicking one of the +destroy+ links sends the associated id to the +destroy+ action:
def destroy
@post = Post.find(params[:id])
@post.destroy
respond_to do |format|
format.html { redirect_to(posts_url) }
format.json { render :json => {}, :status => :ok }
end
end
The +destroy+ method of an Active Record model instance removes the corresponding record from the database. After that's done, there isn't any record to display, so Rails redirects the user's browser to the index view for the model.
h3. Adding a Second Model
Now that you've seen how a model built with scaffolding looks like, it's time to add a second model to the application. The second model will handle comments on blog posts.
h4. Generating a Model
Models in Rails use a singular name, and their corresponding database tables use a plural name. For the model to hold comments, the convention is to use the name Comment. Even if you don't want to use the entire apparatus set up by scaffolding, most Rails developers still use generators to make things like models and controllers. To create the new model, run this command in your terminal:
$ rails generate model Comment commenter:string body:text post:references
This command will generate four files:
* +app/models/comment.rb+ - The model
* +db/migrate/20100207235629_create_comments.rb+ - The migration
* +test/unit/comment_test.rb+ and +test/fixtures/comments.yml+ - The test harness.
First, take a look at +comment.rb+:
class Comment < ActiveRecord::Base
belongs_to :post
end
This is very similar to the +post.rb+ model that you saw earlier. The difference is the line +belongs_to :post+, which sets up an Active Record _association_. You'll learn a little about associations in the next section of this guide.
In addition to the model, Rails has also made a migration to create the corresponding database table:
class CreateComments < ActiveRecord::Migration
def change
create_table :comments do |t|
t.string :commenter
t.text :body
t.references :post
t.timestamps
end
add_index :comments, :post_id
end
end
The +t.references+ line sets up a foreign key column for the association between the two models. And the +add_index+ line sets up an index for this association column. Go ahead and run the migration:
$ rake db:migrate
Rails is smart enough to only execute the migrations that have not already been run against the current database, so in this case you will just see:
== CreateComments: migrating =================================================
-- create_table(:comments)
-> 0.0017s
== CreateComments: migrated (0.0018s) ========================================
h4. Associating Models
Active Record associations let you easily declare the relationship between two models. In the case of comments and posts, you could write out the relationships this way:
* Each comment belongs to one post
* One post can have many comments
In fact, this is very close to the syntax that Rails uses to declare this association. You've already seen the line of code inside the Comment model that makes each comment belong to a Post:
class Comment < ActiveRecord::Base
belongs_to :post
end
You'll need to edit the +post.rb+ file to add the other side of the association:
class Post < ActiveRecord::Base
validates :name, :presence => true
validates :title, :presence => true,
:length => { :minimum => 5 }
has_many :comments
end
These two declarations enable a good bit of automatic behavior. For example, if you have an instance variable +@post+ containing a post, you can retrieve all the comments belonging to that post as the array +@post.comments+.
TIP: For more information on Active Record associations, see the "Active Record Associations":association_basics.html guide.
h4. Adding a Route for Comments
As with the +home+ 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, you will see an entry that was added automatically for +posts+ near the top by the scaffold generator, +resources :posts+, edit it as follows:
resources :posts do
resources :comments
end
This creates +comments+ as a _nested resource_ within +posts+. This is another part of capturing the hierarchical relationship that exists between posts and comments.
TIP: For more information on routing, see the "Rails Routing from the Outside In":routing.html guide.
h4. Generating a Controller
With the model in hand, you can turn your attention to creating a matching controller. Again, there's a generator for this:
$ rails generate controller Comments
This creates four files and one empty directory:
* +app/controllers/comments_controller.rb+ - The controller
* +app/helpers/comments_helper.rb+ - A view helper file
* +test/functional/comments_controller_test.rb+ - The functional tests for the controller
* +test/unit/helpers/comments_helper_test.rb+ - The unit tests for the helper
* +app/views/comments/+ - Views of the controller are stored here
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:
<%= notice %>
Name:
<%= @post.name %>
Title:
<%= @post.title %>
Content:
<%= @post.content %>
Add a comment:
<%= form_for([@post, @post.comments.build]) do |f| %>
<%= f.label :commenter %>
<%= f.text_field :commenter %>
<%= f.label :body %>
<%= f.text_area :body %>
<%= f.submit %>
<% end %>
<%= link_to 'Edit Post', edit_post_path(@post) %> |
<%= link_to 'Back to Posts', posts_path %> |
This adds a form on the Post show page that creates a new comment, which will call the +CommentsController+ +create+ action, so let's wire that up:
class CommentsController < ApplicationController
def create
@post = Post.find(params[:post_id])
@comment = @post.comments.create(params[:comment])
redirect_to post_path(@post)
end
end
You'll see a bit more complexity here than you did in the controller for posts. That's a side-effect of the nesting that you've set up; each request for a comment has to keep track of the post to which the comment is attached, thus the initial find action to 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+.
<%= notice %>
Name:
<%= @post.name %>
Title:
<%= @post.title %>
Content:
<%= @post.content %>
Comments
<% @post.comments.each do |comment| %>
Commenter:
<%= comment.commenter %>
Comment:
<%= comment.body %>
<% end %>
Add a comment:
<%= form_for([@post, @post.comments.build]) do |f| %>
<%= f.label :commenter %>
<%= f.text_field :commenter %>
<%= f.label :body %>
<%= f.text_area :body %>
<%= f.submit %>
<% end %>
<%= link_to 'Edit Post', edit_post_path(@post) %> |
<%= link_to 'Back to Posts', posts_path %> |
Now you can add posts and comments to your blog and have them show up in the right places.
h3. Refactoring
Now that we have Posts and Comments working, if we take a look at the +app/views/posts/show.html.erb+ template, it's getting long and awkward. We can use partials to clean this up.
h4. Rendering Partial Collections
First we will make a comment partial to extract showing all the comments for the post. Create the file +app/views/comments/_comment.html.erb+ and put the following into it:
Commenter:
<%= comment.commenter %>
Comment:
<%= comment.body %>
Then in the +app/views/posts/show.html.erb+ you can change it to look like the following:
<%= notice %>
Name:
<%= @post.name %>
Title:
<%= @post.title %>
Content:
<%= @post.content %>
Comments
<%= render @post.comments %>
Add a comment:
<%= form_for([@post, @post.comments.build]) do |f| %>
<%= f.label :commenter %>
<%= f.text_field :commenter %>
<%= f.label :body %>
<%= f.text_area :body %>
<%= f.submit %>
<% end %>
<%= link_to 'Edit Post', edit_post_path(@post) %> |
<%= link_to 'Back to Posts', posts_path %> |
This will now render the partial in +app/views/comments/_comment.html.erb+ once for each comment that is in the +@post.comments+ collection. As the +render+ method iterates over the @post.comments collection, it assigns each comment to a local variable named the same as the partial, in this case +comment+ which is then available in the partial for us to show.
h4. Rendering a Partial Form
Lets also move that new comment section out to it's own partial, again, you create a file +app/views/comments/_form.html.erb+ and in it you put:
<%= form_for([@post, @post.comments.build]) do |f| %>
<%= f.label :commenter %>
<%= f.text_field :commenter %>
<%= f.label :body %>
<%= f.text_area :body %>
<%= f.submit %>
<% end %>
Then you make the +app/views/posts/show.html.erb+ look like the following:
<%= notice %>
Name:
<%= @post.name %>
Title:
<%= @post.title %>
Content:
<%= @post.content %>
Comments
<%= render @post.comments %>
Add a comment:
<%= render "comments/form" %>
<%= link_to 'Edit Post', edit_post_path(@post) %> |
<%= link_to 'Back to Posts', posts_path %> |
The second render just defines the partial template we want to render, comments/form, Rails is smart enough to spot the forward slash in that string and realize that you want to render the _form.html.erb file in the app/views/comments directory.
The +@post+ object is available to any partials rendered in the view because we defined it as an instance variable.
h3. Deleting Comments
Another important feature on a blog is being able to delete SPAM comments. To do this, we need to implement a link of some sort in the view and a +DELETE+ action in the +CommentsController+.
So first, let's add the delete link in the +app/views/comments/_comment.html.erb+ partial:
Commenter:
<%= comment.commenter %>
Comment:
<%= comment.body %>
<%= link_to 'Destroy Comment', [comment.post, comment],
:confirm => 'Are you sure?',
:method => :delete %>
Clicking this new "Destroy Comment" link will fire off a DELETE /posts/:id/comments/:id to our +CommentsController+, which can then use this to find the comment we want to delete, so let's add a destroy action to our controller:
class CommentsController < ApplicationController
def create
@post = Post.find(params[:post_id])
@comment = @post.comments.create(params[:comment])
redirect_to post_path(@post)
end
def destroy
@post = Post.find(params[:post_id])
@comment = @post.comments.find(params[:id])
@comment.destroy
redirect_to post_path(@post)
end
end
The +destroy+ action will find the post we are looking at, locate the comment within the @post.comments collection, and then remove it from the database and send us back to the show action for the post.
h4. Deleting Associated Objects
If you delete a post then its associated comments will also need to be deleted. Otherwise they would simply occupy space in the database. Rails allows you to use the +dependent+ option of an association to achieve this. Modify the Post model, +app/models/post.rb+, as follows:
class Post < ActiveRecord::Base
validates :name, :presence => true
validates :title, :presence => true,
:length => { :minimum => 5 }
has_many :comments, :dependent => :destroy
end
h3. Security
If you were to publish your blog online, anybody would be able to add, edit and delete posts or delete comments.
Rails provides a very simple HTTP authentication system that will work nicely in this situation.
In the +PostsController+ we need to have a way to block access to the various actions if the person is not authenticated, here we can use the Rails http_basic_authenticate_with method, allowing access to the requested action if that method allows it.
To use the authentication system, we specify it at the top of our +PostsController+, in this case, we want the user to be authenticated on every action, except for +index+ and +show+, so we write that:
class PostsController < ApplicationController
http_basic_authenticate_with :name => "dhh", :password => "secret", :except => :index
# GET /posts
# GET /posts.json
def index
@posts = Post.all
respond_to do |format|
# snipped for brevity
We also only want to allow authenticated users to delete comments, so in the +CommentsController+ we write:
class CommentsController < ApplicationController
http_basic_authenticate_with :name => "dhh", :password => "secret", :only => :destroy
def create
@post = Post.find(params[:post_id])
# snipped for brevity
Now if you try to create a new post, you will be greeted with a basic HTTP Authentication challenge
!images/challenge.png(Basic HTTP Authentication Challenge)!
h3. Building a Multi-Model Form
Another feature of your average blog is the ability to tag posts. To implement this feature your application needs to interact with more than one model on a single form. Rails offers support for nested forms.
To demonstrate this, we will add support for giving each post multiple tags, right in the form where you create the post. First, create a new model to hold the tags:
$ rails generate model tag name:string post:references
Again, run the migration to create the database table:
$ rake db:migrate
Next, edit the +post.rb+ file to create the other side of the association, and to tell Rails (via the +accepts_nested_attributes_for+ macro) that you intend to edit tags via posts:
class Post < ActiveRecord::Base
validates :name, :presence => true
validates :title, :presence => true,
:length => { :minimum => 5 }
has_many :comments, :dependent => :destroy
has_many :tags
accepts_nested_attributes_for :tags, :allow_destroy => :true,
:reject_if => proc { |attrs| attrs.all? { |k, v| v.blank? } }
end
The +:allow_destroy+ option on the nested attribute declaration tells Rails to display a "remove" checkbox on the view that you'll build shortly. The +:reject_if+ option prevents saving new tags that do not have any attributes filled in.
We will modify +views/posts/_form.html.erb+ to render a partial to make a tag:
<% @post.tags.build %>
<%= form_for(@post) do |post_form| %>
<% if @post.errors.any? %>
<%= pluralize(@post.errors.count, "error") %> prohibited this post from being saved:
<% @post.errors.full_messages.each do |msg| %>
- <%= msg %>
<% end %>
<% end %>
<%= post_form.label :name %>
<%= post_form.text_field :name %>
<%= post_form.label :title %>
<%= post_form.text_field :title %>
<%= post_form.label :content %>
<%= post_form.text_area :content %>
Tags
<%= render :partial => 'tags/form',
:locals => {:form => post_form} %>
<%= post_form.submit %>
<% end %>
Note that we have changed the +f+ in +form_for(@post) do |f|+ to +post_form+ to make it easier to understand what is going on.
This example shows another option of the render helper, being able to pass in local variables, in this case, we want the local variable +form+ in the partial to refer to the +post_form+ object.
We also add a @post.tags.build at the top of this form, this is to make sure there is a new tag ready to have it's name filled in by the user. If you do not build the new tag, then the form will not appear as there is no new Tag object ready to create.
Now create the folder app/views/tags and make a file in there called _form.html.erb which contains the form for the tag:
<%= form.fields_for :tags do |tag_form| %>
<%= tag_form.label :name, 'Tag:' %>
<%= tag_form.text_field :name %>
<% unless tag_form.object.nil? || tag_form.object.new_record? %>
<%= tag_form.label :_destroy, 'Remove:' %>
<%= tag_form.check_box :_destroy %>
<% end %>
<% end %>
Finally, we will edit the app/views/posts/show.html.erb template to show our tags.
<%= notice %>
Name:
<%= @post.name %>
Title:
<%= @post.title %>
Content:
<%= @post.content %>
Tags:
<%= @post.tags.map { |t| t.name }.join(", ") %>
Comments
<%= render @post.comments %>
Add a comment:
<%= render "comments/form" %>
<%= link_to 'Edit Post', edit_post_path(@post) %> |
<%= link_to 'Back to Posts', posts_path %> |
With these changes in place, you'll find that you can edit a post and its tags directly on the same view.
However, that method call @post.tags.map { |t| t.name }.join(", ") is awkward, we could handle this by making a helper method.
h3. View Helpers
View Helpers live in app/helpers and provide small snippets of reusable code for views. In our case, we want a method that strings a bunch of objects together using their name attribute and joining them with a comma. As this is for the Post show template, we put it in the PostsHelper.
Open up app/helpers/posts_helper.rb and add the following:
module PostsHelper
def join_tags(post)
post.tags.map { |t| t.name }.join(", ")
end
end
Now you can edit the view in app/views/posts/show.html.erb to look like this:
<%= notice %>
Name:
<%= @post.name %>
Title:
<%= @post.title %>
Content:
<%= @post.content %>
Tags:
<%= join_tags(@post) %>
Comments
<%= render @post.comments %>
Add a comment:
<%= render "comments/form" %>
<%= link_to 'Edit Post', edit_post_path(@post) %> |
<%= link_to 'Back to Posts', posts_path %> |
h3. What's Next?
Now that you've seen your first Rails application, you should feel free to update it and experiment on your own. But you don't have to do everything without help. As you need assistance getting up and running with Rails, feel free to consult these support resources:
* The "Ruby on Rails guides":index.html
* The "Ruby on Rails Tutorial":http://railstutorial.org/book
* The "Ruby on Rails mailing list":http://groups.google.com/group/rubyonrails-talk
* The "#rubyonrails":irc://irc.freenode.net/#rubyonrails channel on irc.freenode.net
* The "Rails Wiki":http://wiki.rubyonrails.org/
Rails also comes with built-in help that you can generate using the rake command-line utility:
* Running +rake doc:guides+ will put a full copy of the Rails Guides in the +doc/guides+ folder of your application. Open +doc/guides/index.html+ in your web browser to explore the Guides.
* Running +rake doc:rails+ will put a full copy of the API documentation for Rails in the +doc/api+ folder of your application. Open +doc/api/index.html+ in your web browser to explore the API documentation.
h3. Configuration Gotchas
The easiest way to work with Rails is to store all external data as UTF-8. If you don't, Ruby libraries and Rails will often be able to convert your native data into UTF-8, but this doesn't always work reliably, so you're better off ensuring that all external data is UTF-8.
If you have made a mistake in this area, the most common symptom is a black diamond with a question mark inside appearing in the browser. Another common symptom is characters like "ü" appearing instead of "ü". Rails takes a number of internal steps to mitigate common causes of these problems that can be automatically detected and corrected. However, if you have external data that is not stored as UTF-8, it can occasionally result in these kinds of issues that cannot be automatically detected by Rails and corrected.
Two very common sources of data that are not UTF-8:
* Your text editor: Most text editors (such as Textmate), default to saving files as
UTF-8. If your text editor does not, this can result in special characters that you
enter in your templates (such as é) to appear as a diamond with a question mark inside
in the browser. This also applies to your I18N translation files.
Most editors that do not already default to UTF-8 (such as some versions of
Dreamweaver) offer a way to change the default to UTF-8. Do so.
* Your database. Rails defaults to converting data from your database into UTF-8 at
the boundary. However, if your database is not using UTF-8 internally, it may not
be able to store all characters that your users enter. For instance, if your database
is using Latin-1 internally, and your user enters a Russian, Hebrew, or Japanese
character, the data will be lost forever once it enters the database. If possible,
use UTF-8 as the internal storage of your database.
h3. Changelog
* April 26, 2011: Change migration code from +up+, +down+ pair to +change+ method by "Prem Sichanugrist":http://sikachu.com
* April 11, 2011: Change scaffold_controller generator to create format block for JSON instead of XML by "Sebastian Martinez":http://www.wyeworks.com
* August 30, 2010: Minor editing after Rails 3 release by "Joost Baaij":http://www.spacebabies.nl
* July 12, 2010: Fixes, editing and updating of code samples by "Jaime Iniesta":http://jaimeiniesta.com
* May 16, 2010: Added a section on configuration gotchas to address common encoding problems that people might have by "Yehuda Katz":http://www.yehudakatz.com
* April 30, 2010: Fixes, editing and updating of code samples by "Rohit Arondekar":http://rohitarondekar.com
* April 25, 2010: Couple of more minor fixups by "Mikel Lindsaar":credits.html#raasdnil
* April 1, 2010: Fixed document to validate XHTML 1.0 Strict by "Jaime Iniesta":http://jaimeiniesta.com
* February 8, 2010: Full re-write for Rails 3.0-beta, added helpers and before_filters, refactored code by "Mikel Lindsaar":credits.html#raasdnil
* January 24, 2010: Re-write for Rails 3.0 by "Mikel Lindsaar":credits.html#raasdnil
* July 18, 2009: Minor cleanup in anticipation of Rails 2.3.3 by "Mike Gunderloy":credits.html#mgunderloy
* February 1, 2009: Updated for Rails 2.3 by "Mike Gunderloy":credits.html#mgunderloy
* November 3, 2008: Formatting patch from Dave Rothlisberger
* November 1, 2008: First approved version by "Mike Gunderloy":credits.html#mgunderloy
* October 16, 2008: Revised based on feedback from Pratik Naik by "Mike Gunderloy":credits.html#mgunderloy (not yet approved for publication)
* October 13, 2008: First complete draft by "Mike Gunderloy":credits.html#mgunderloy (not yet approved for publication)
* October 12, 2008: More detail, rearrangement, editing by "Mike Gunderloy":credits.html#mgunderloy (not yet approved for publication)
* September 8, 2008: initial version by "James Miller":credits.html#bensie (not yet approved for publication)