Getting Started With Rails ========================== This guide covers getting up and running with Ruby on Rails. After reading it, you should be familiar with: * Installing Rails, creating a new Rails application, and connecting your application to a database * The general layout of a Rails application * The basic principles of MVC (Model, View Controller) and RESTful design * How to quickly generate the starting pieces of a Rails application. NOTE: This Guide is based on Rails 2.3. Some of the code shown here will not work in older versions of Rails. == This Guide Assumes 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 link:http://www.ruby-lang.org/en/downloads/[Ruby] language * The link:http://rubyforge.org/frs/?group_id=126[RubyGems] packaging system * A working installation of link:http://www.sqlite.org/[SQLite] (preferred), link:http://www.mysql.com/[MySQL], or link:http://www.postgresql.org/[PostgreSQL] It is highly recommended that you *familiarize yourself with Ruby before diving into Rails*. You will find it much easier to follow what's going on with a Rails application if you understand basic Ruby syntax. Rails isn't going to magically revolutionize the way you write web applications if you have no experience with the language it uses. There are some good free resources on the internet for learning Ruby, including: * link:http://www.humblelittlerubybook.com/[Mr. Neigborly’s Humble Little Ruby Book] * link:http://www.rubycentral.com/book/[Programming Ruby] * link:http://poignantguide.net/ruby/[Why's (Poignant) Guide to Ruby] == What is Rails? Rails is a web development framework written in the Ruby language. It is designed to make programming web applications easier by making several 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. Longtime Rails developers also report that it makes web application development more fun. Rails is _opinionated software_. That is, it assumes that there is a best way to do things, and it's designed to encourage that best 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 several 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 letting you tweak every little thing through endless configuration files. * REST is the best pattern for web applications - organizing your application around resources and standard HTTP verbs is the fastest way to go. === The MVC Architecture Rails is organized around the Model, View, Controller architecture, usually just called MVC. MVC benefits include: * Isolation of business logic from the user interface * Ease of keeping code DRY * Making it clear where different types of code belong for easier maintenance ==== Models A model represents the information (data) of the application and the rules to manipulate that data. In the case of Rails, models are primarily used for managing the rules of interaction with a corresponding database table. In most cases, one table in your database will correspond to one model in your application. The bulk of your application's business logic will be concentrated in the models. ==== Views Views represent the user interface of your application. In Rails, views are often HTML files with embedded Ruby code that performs tasks related solely to the presentation of the data. Views handle the job of providing data to the web browser or other tool that is used to make requests from your application. ==== Controllers Controllers provide the "glue" between models and views. In Rails, controllers are responsible for processing the incoming requests from the web browser, interrogating the models for data, and passing that data on to the views for presentation. === The Components of Rails Rails provides a full stack of components for creating web applications, including: * Action Controller * Action View * Active Record * Action Mailer * Active Resource * Railties * Active Support ==== Action Controller Action Controller is the component that manages the controllers in a Rails application. The Action Controller framework processes incoming requests to a Rails application, extracts parameters, and dispatches them to the intended action. Services provided by Action Controller include session management, template rendering, and redirect management. ==== Action View Action View manages the views of your Rails application. It can create both HTML and XML output by default. Action View manages rendering templates, including nested and partial templates, and includes built-in AJAX support. ==== Active Record Active Record is the base for the models in a Rails application. It provides database independence, basic CRUD functionality, advanced finding capabilities, and the ability to relate models to one another, among other services. ==== Action Mailer Action Mailer is a framework for building e-mail services. You can use Action Mailer to send emails based on flexible templates, or to receive and process incoming email. ==== Active Resource Active Resource provides a framework for managing the connection between business objects an RESTful web services. It implements a way to map web-based resources to local objects with CRUD semantics. ==== Railties Railties is the core Rails code that builds new Rails applications and glues the various frameworks together in any Rails application. ==== Active Support Active Support is an extensive collection of utility classes and standard Ruby library extensions that are used in the Rails, both by the core code and by your applications. === REST The foundation of the RESTful architecture is generally considered to be Roy Fielding's doctoral thesis, link:http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm[Architectural Styles and the Design of Network-based Software Architectures]. Fortunately, you need not read this entire document to understand how REST works in Rails. REST, an acronym for Representational State Transfer, boils down to two main principles for our purposes: * Using resource identifiers (which, for the purposes of discussion, you can think of as URLs) to represent resources * Transferring representations of the state of that resource between system components. For example, to a Rails application a request such as this: +DELETE /photos/17+ would be understood to refer to a photo resource with the ID of 17, and to indicate a desired action - deleting that resource. REST is a natural style for the architecture of web applications, and Rails makes it even more natural by using conventions to shield you from some of the RESTful complexities and browser quirks. If you’d like more details on REST as an architectural style, these resources are more approachable than Fielding’s thesis: * link:http://www.infoq.com/articles/rest-introduction[A Brief Introduction to REST] by Stefan Tilkov * link:http://bitworking.org/news/373/An-Introduction-to-REST[An Introduction to REST] (video tutorial) by Joe Gregorio * link:http://en.wikipedia.org/wiki/Representational_State_Transfer[Representational State Transfer] article in Wikipedia == Creating a New Rails Project If you follow 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. === Installing Rails In most cases, the easiest way to install Rails is to take advantage of RubyGems: [source, shell] ------------------------------------------------------- $ gem install rails ------------------------------------------------------- NOTE: There are some special circumstances in which you might want to use an alternate installation strategy: * If you're working on Windows, you may find it easier to install link:http://instantrails.rubyforge.org/wiki/wiki.pl[Instant Rails]. Be aware, though, that Instant Rails releases tend to lag seriously behind the actual Rails version. Also, you will find that Rails development on Windows is overall less pleasant than on other operating systems. If at all possible, we suggest that you install a Linux virtual machine and use that for Rails development, instead of using Windows. * If you want to keep up with cutting-edge changes to Rails, you'll want to clone the link:http://github.com/rails/rails/tree/master[Rails source code] from github. This is not recommended as an option for beginners, though. === Creating the Blog Application Open a terminal, navigate to a folder where you have rights to create files, and type: [source, shell] ------------------------------------------------------- $ rails blog ------------------------------------------------------- This will create a Rails application that uses a SQLite database for data storage. If you prefer to use MySQL, run this command instead: [source, shell] ------------------------------------------------------- $ rails blog -d mysql ------------------------------------------------------- And if you're using PostgreSQL for data storage, run this command: [source, shell] ------------------------------------------------------- $ rails blog -d postgresql ------------------------------------------------------- TIP: You can see all of the switches that the Rails application builder accepts by running +rails -h+. After you create the blog application, switch to its folder to continue work directly in that application: [source, shell] ------------------------------------------------------- $ cd blog ------------------------------------------------------- In any case, Rails will create a folder in your working directory called +blog+. Open up that folder and explore its contents. Most of the work in this tutorial will happen in the +app/+ folder, but here's a basic rundown on the function of each folder that Rails creates in a new application by default: [options="header"] |========================================================================================================== |File/Folder |Purpose |+README+ |This is a brief instruction manual for your application. Use it to tell others what your application does, how to set it up, and so on. |+Rakefile+ |This file contains batch jobs that can be run from the terminal. |+app/+ |Contains the controllers, models, and views 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. |+db/+ |Shows your current database schema, as well as the database migrations. You'll learn about migrations shortly. |+doc/+ |In-depth documentation for your application. |+lib/+ |Extended modules for your application (not covered in this guide). |+log/+ |Application log files. |+public/+ |The only folder seen to the world as-is. This is where your images, javascript, stylesheets (CSS), and other static files go. |+script/+ |Scripts provided by Rails to do recurring tasks, such as benchmarking, plugin installation, and starting the console or the web server. |+test/+ |Unit tests, fixtures, and other test apparatus. These are covered in link:../testing_rails_applications.html[Testing Rails Applications] |+tmp/+ |Temporary files |+vendor/+ |A place for third-party code. In a typical Rails application, this includes Ruby Gems, the Rails source code (if you install it into your project) and plugins containing additional prepackaged functionality. |========================================================================================================== === Configuring a Database Just about every Rails application will interact with a database. The database to use is specified in a configuration file, +config/database.yml+. If you open this file in a new Rails application, you'll see a default database configuration using SQLite. The file contains sections for three different environments in which Rails can run by default: * The +development+ environment is used on your development computer as you interact manually with the application * The +test+ environment is used to run automated tests * The +production+ environment is used when you deploy your application for the world to use. ==== Configuring a SQLite Database Rails comes with built-in support for link:http://www.sqlite.org/[SQLite], which is a lightweight serverless database application. While a busy production environment may overload SQLite, it works well for development and testing. Rails defaults to using a SQLite database when creating a new project, but you can always change it later. Here's the section of the default configuration file with connection information for the development environment: [source, ruby] ------------------------------------------------------- development: adapter: sqlite3 database: db/development.sqlite3 pool: 5 timeout: 5000 ------------------------------------------------------- If you don't have any database set up, SQLite is the easiest to get installed. If you're on OS X 10.5 or greater on a Mac, you already have it. Otherwise, you can install it using RubyGems: [source, shell] ------------------------------------------------------- $ gem install sqlite3-ruby ------------------------------------------------------- ==== Configuring a MySQL Database If you choose to use MySQL, your +config/database.yml+ will look a little different. Here's the development section: [source, ruby] ------------------------------------------------------- development: adapter: mysql encoding: utf8 database: blog_development pool: 5 username: root password: socket: /tmp/mysql.sock ------------------------------------------------------- If your development computer's MySQL installation includes a root user with an empty password, this configuration should work for you. Otherwise, change the username and password in the +development+ section as appropriate. ==== Configuring a PostgreSQL Database If you choose to use PostgreSQL, your +config/database.yml+ will be customized to use PostgreSQL databases: [source, ruby] ------------------------------------------------------- development: adapter: postgresql encoding: unicode database: blog_development pool: 5 username: blog password: ------------------------------------------------------- Change the username and password in the +development+ section as appropriate. ==== 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: [source, shell] ------------------------------------------------------- $ rake db:create ------------------------------------------------------- NOTE: 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+. == Hello, Rails! One of the traditional places to start with a new language is by getting some text up on screen quickly. To do that in Rails, 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: [source, shell] ------------------------------------------------------- $ script/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 +script+ commands to Ruby: +ruby script/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: [source, html] -------------------------------------------------------
Name | Title | Content | |||
---|---|---|---|---|---|
<%=h post.name %> | <%=h post.title %> | <%=h post.content %> | <%= link_to 'Show', post %> | <%= link_to 'Edit', edit_post_path(post) %> | <%= link_to 'Destroy', post, :confirm => 'Are you sure?', :method => :delete %> |
<%= flash[:notice] %>
<%= 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. === Creating New Posts Creating a new post involves two actions. The first is the +new+ action, which instantiates an empty +Post+ object: [source, ruby] ------------------------------------------------------- def new @post = Post.new respond_to do |format| format.html # new.html.erb format.xml { render :xml => @post } end end ------------------------------------------------------- The +new.html.erb+ view displays this empty Post to the user: [source, ruby] -------------------------------------------------------
<%= f.label :name %>
<%= f.text_field :name %>
<%= f.label :title %>
<%= f.text_field :title %>
<%= f.label :content %>
<%= f.text_area :content %>
<%= f.submit "Create" %>
<% end %> <%= link_to 'Back', posts_path %> ------------------------------------------------------- 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 your write raw HTML because the code is more succinct, and because it explicitly ties the form to a particular model instance. 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+ 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): [source, ruby] ------------------------------------------------------- def create @post = Post.new(params[:post]) respond_to do |format| if @post.save flash[:notice] = 'Post was successfully created.' format.html { redirect_to(@post) } format.xml { render :xml => @post, :status => :created, :location => @post } else format.html { render :action => "new" } format.xml { render :xml => @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 saving the new post, it uses +flash[:notice]+ to create an informational message for the user, and redirects to the show action for the post. If there's any problem, the +create+ action just shows the +new+ view a second time, with any error messages. Rails provides the +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." === 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: [source, ruby] ------------------------------------------------------- def show @post = Post.find(params[:id]) respond_to do |format| format.html # show.html.erb format.xml { render :xml => @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+: [source, ruby] -------------------------------------------------------Name: <%=h @post.name %>
Title: <%=h @post.title %>
Content: <%=h @post.content %>
<%= link_to 'Edit', edit_post_path(@post) %> | <%= link_to 'Back', posts_path %> ------------------------------------------------------- === 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: [source, ruby] ------------------------------------------------------- def edit @post = Post.find(params[:id]) end ------------------------------------------------------- After finding the requested post, Rails uses the +edit.html.erb+ view to display it: [source, ruby] -------------------------------------------------------
<%= f.label :name %>
<%= f.text_field :name %>
<%= f.label :title %>
<%= f.text_field :title %>
<%= f.label :content %>
<%= f.text_area :content %>
<%= f.submit "Update" %>
<% end %> <%= link_to 'Show', @post %> | <%= link_to 'Back', posts_path %> ------------------------------------------------------- Submitting the form created by this view will invoke the +update+ action within the controller: [source, ruby] ------------------------------------------------------- def update @post = Post.find(params[:id]) respond_to do |format| if @post.update_attributes(params[:post]) flash[:notice] = 'Post was successfully updated.' format.html { redirect_to(@post) } format.xml { head :ok } else format.html { render :action => "edit" } format.xml { render :xml => @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 +edit+ to correct them. NOTE: Sharp-eyed readers will have noticed that the +form_for+ declaration is identical for the +new+ and +edit+ views. Rails generates different code for the two forms because it's smart enough to notice that in the one case it's being passed a new record that has never been saved, and in the other case an existing record that has already been saved to the database. In a production Rails application, you would ordinarily eliminate this duplication by moving identical code to a _partial template_, which you could then include in both parent templates. But the scaffold generator tries not to make too many assumptions, and generates code that’s easy to modify if you want different forms for +create+ and +edit+. === Destroying a Post Finally, clicking one of the +destroy+ links sends the associated id to the +destroy+ action: [source, ruby] ------------------------------------------------------- def destroy @post = Post.find(params[:id]) @post.destroy respond_to do |format| format.html { redirect_to(posts_url) } format.xml { head :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. == DRYing up the Code At this point, it’s worth looking at some of the tools that Rails provides to eliminate duplication in your code. In particular, you can use _partials_ to clean up duplication in views and _filters_ to help with duplication in controllers. === Using Partials to Eliminate View Duplication As you saw earlier, the scaffold-generated views for the +new+ and +edit+ actions are largely identical. You can pull the shared code out into a partial template. This requires editing the new and edit views, and adding a new template. The new +_form.html.erb+ template should be saved in the same +app/views/posts+ folder as the files from which it is being extracted. Note that the name of this file begins with an underscore; that's the Rails naming convention for partial templates. +new.html.erb+: [source, ruby] -------------------------------------------------------
<%= f.label :name %>
<%= f.text_field :name %>
<%= f.label :title, "title" %>
<%= f.text_field :title %>
<%= f.label :content %>
<%= f.text_area :content %>
<%= f.submit "Save" %>
<% end %> ------------------------------------------------------- Now, when Rails renders the +new+ or +edit+ view, it will insert the +_form+ partial at the indicated point. Note the naming convention for partials: if you refer to a partial named +form+ inside of a view, the corresponding file is +_form.html.erb+, with a leading underscore. For more information on partials, refer to the link:../layouts_and_rendering.html[Layouts and Rending in Rails] guide. === Using Filters to Eliminate Controller Duplication At this point, if you look at the controller for posts, you’ll see some duplication: [source, ruby] ------------------------------------------------------- class PostsController < ApplicationController # ... def show @post = Post.find(params[:id]) # ... end def edit @post = Post.find(params[:id]) end def update @post = Post.find(params[:id]) # ... end def destroy @post = Post.find(params[:id]) # ... end end ------------------------------------------------------- Four instances of the exact same line of code doesn’t seem very DRY. Rails provides _filters_ as a way to address this sort of repeated code. In this case, you can DRY things up by using a +before_filter+: [source, ruby] ------------------------------------------------------- class PostsController < ApplicationController before_filter :find_post, :only => [:show, :edit, :update, :destroy] # ... def show # ... end def edit end def update # ... end def destroy # ... end private def find_post @post = Post.find(params[:id]) end end ------------------------------------------------------- Rails runs _before filters_ before any action in the controller. You can use the +:only+ clause to limit a before filter to only certain actions, or an +:except+ clause to specifically skip a before filter for certain actions. Rails also allows you to define _after filters_ that run after processing an action, as well as _around filters_ that surround the processing of actions. Filters can also be defined in external classes to make it easy to share them between controllers. For more information on filters, see the link:../actioncontroller_basics.html[Action Controller Basics] guide. == Adding a Second Model Now that you've seen what's in a model built with scaffolding, it's time to add a second model to the application. The second model will handle comments on blog posts. === 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: [source, shell] ------------------------------------------------------- $ script/generate model Comment commenter:string body:text post:references ------------------------------------------------------- This command will generate four files: * +app/models/comment.rb+ - The model * +db/migrate/20091013214407_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+: [source, ruby] ------------------------------------------------------- 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: [source, ruby] ------------------------------------------------------- class CreateComments < ActiveRecord::Migration def self.up create_table :comments do |t| t.string :commenter t.text :body t.references :post t.timestamps end end def self.down drop_table :comments end end ------------------------------------------------------- The +t.references+ line sets up a foreign key column for the association between the two models. Go ahead and run the migration: [source, shell] ------------------------------------------------------- $ rake db:migrate ------------------------------------------------------- Rails is smart enough to only execute the migrations that have not already been run against the current database. === 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: [source, ruby] ------------------------------------------------------- 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: [source, ruby] ------------------------------------------------------- class Post < ActiveRecord::Base validates_presence_of :name, :title validates_length_of :title, :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 link:../association_basics.html[Active Record Associations] guide. === Adding a Route _Routes_ are entries in the +config/routes.rb+ file that tell Rails how to match incoming HTTP requests to controller actions. Open up that file and find the existing line referring to +posts+ (it will be right at the top of the file). Then edit it as follows: [source, ruby] ------------------------------------------------------- map.resources :posts, :has_many => :comments ------------------------------------------------------- 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 link:../routing_outside_in.html[Rails Routing from the Outside In] guide. === 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: [source, shell] ------------------------------------------------------- $ script/generate controller Comments index show new edit ------------------------------------------------------- This creates seven files: * +app/controllers/comments_controller.rb+ - The controller * +app/helpers/comments_helper.rb+ - A view helper file * +app/views/comments/index.html.erb+ - The view for the index action * +app/views/comments/show.html.erb+ - The view for the show action * +app/views/comments/new.html.erb+ - The view for the new action * +app/views/comments/edit.html.erb+ - The view for the edit action * +test/functional/comments_controller_test.rb+ - The functional tests for the controller The controller will be generated with empty methods and views for each action that you specified in the call to +script/generate controller+: [source, ruby] ------------------------------------------------------- class CommentsController < ApplicationController def index end def show end def new end def edit end end ------------------------------------------------------- You'll need to flesh this out with code to actually process requests appropriately in each method. Here's a version that (for simplicity's sake) only responds to requests that require HTML: [source, ruby] ------------------------------------------------------- class CommentsController < ApplicationController def index @post = Post.find(params[:post_id]) @comments = @post.comments end def show @post = Post.find(params[:post_id]) @comment = @post.comments.find(params[:id]) end def new @post = Post.find(params[:post_id]) @comment = @post.comments.build end def create @post = Post.find(params[:post_id]) @comment = @post.comments.build(params[:comment]) if @comment.save redirect_to post_comment_url(@post, @comment) else render :action => "new" end end def edit @post = Post.find(params[:post_id]) @comment = @post.comments.find(params[:id]) end def update @post = Post.find(params[:post_id]) @comment = Comment.find(params[:id]) if @comment.update_attributes(params[:comment]) redirect_to post_comment_url(@post, @comment) else render :action => "edit" end end def destroy @post = Post.find(params[:post_id]) @comment = Comment.find(params[:id]) @comment.destroy respond_to do |format| format.html { redirect_to post_comments_path(@post) } format.xml { head :ok } end 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. In addition, the code takes advantage of some of the methods available for an association. For example, in the +new+ method, it calls [source, ruby] ------------------------------------------------------- @comment = @post.comments.build ------------------------------------------------------- This creates a new +Comment+ object _and_ sets up the +post_id+ field to have the +id+ from the specified +Post+ object in a single operation. === Building Views Because you skipped scaffolding, you'll need to build views for comments "by hand." Invoking +script/generate controller+ will give you skeleton views, but they'll be devoid of actual content. Here's a first pass at fleshing out the comment views. The +views/comments/index.html.erb+ view: [source, ruby] -------------------------------------------------------Commenter | Body | |||
---|---|---|---|---|
<%=h comment.commenter %> | <%=h comment.body %> | <%= link_to 'Show', post_comment_path(@post, comment) %> | <%= link_to 'Edit', edit_post_comment_path(@post, comment) %> | <%= link_to 'Destroy', post_comment_path(@post, comment), :confirm => 'Are you sure?', :method => :delete %> |
<%= f.label :commenter %>
<%= f.text_field :commenter %>
<%= f.label :body %>
<%= f.text_area :body %>
<%= f.submit "Create" %>
<% end %> <%= link_to 'Back', post_comments_path(@post) %> ------------------------------------------------------- The +views/comments/show.html.erb+ view: [source, ruby] -------------------------------------------------------Commenter: <%=h @comment.commenter %>
Comment: <%=h @comment.body %>
<%= link_to 'Edit', edit_post_comment_path(@post, @comment) %> | <%= link_to 'Back', post_comments_path(@post) %> ------------------------------------------------------- The +views/comments/edit.html.erb+ view: [source, ruby] -------------------------------------------------------
<%= f.label :commenter %>
<%= f.text_field :commenter %>
<%= f.label :body %>
<%= f.text_area :body %>
<%= f.submit "Update" %>
<% end %> <%= link_to 'Show', post_comment_path(@post, @comment) %> | <%= link_to 'Back', post_comments_path(@post) %> ------------------------------------------------------- Again, the added complexity here (compared to the views you saw for managing posts) comes from the necessity of juggling a post and its comments at the same time. === Hooking Comments to Posts As a next step, I'll modify the +views/posts/show.html.erb+ view to show the comments on that post, and to allow managing those comments: [source, ruby] -------------------------------------------------------Name: <%=h @post.name %>
Title: <%=h @post.title %>
Content: <%=h @post.content %>
Commenter: <%=h c.commenter %>
Comment: <%=h c.body %>
<% end %> <%= link_to 'Edit Post', edit_post_path(@post) %> | <%= link_to 'Back to Posts', posts_path %> | <%= link_to 'Manage Comments', post_comments_path(@post) %> ------------------------------------------------------- Note that each post has its own individual comments collection, accessible as +@post.comments+. That's a consequence of the declarative associations in the models. Path helpers such as +post_comments_path+ come from the nested route declaration in +config/routes.rb+. == Building a Multi-Model Form Comments and posts are edited on two separate forms - which makes sense, given the flow of this mini-application. But what if you want to edit more than one thing on a single form? Rails 2.3 offers new support for nested forms. Let's 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: [source, shell] ------------------------------------------------------- $ script/generate model tag name:string post:references ------------------------------------------------------- Run the migration to create the database table: [source, shell] ------------------------------------------------------- $ rake db:migrate ------------------------------------------------------- Next, edit the +post.rb+ file to create the other side of the association, and to tell Rails that you intend to edit tags via posts: [source, ruby] ------------------------------------------------------- class Post < ActiveRecord::Base validates_presence_of :name, :title validates_length_of :title, :minimum => 5 has_many :comments 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. You'll also need to modify +views/posts/_form.html.erb+ to include the tags: [source, ruby] ------------------------------------------------------- <% @post.tags.build if @post.tags.empty? %> <% form_for(@post) do |post_form| %> <%= post_form.error_messages %>
<%= post_form.label :name %>
<%= post_form.text_field :name %>
<%= post_form.label :title, "title" %>
<%= post_form.text_field :title %>
<%= post_form.label :content %>
<%= post_form.text_area :content %>
<%= tag_form.label :name, 'Tag:' %> <%= tag_form.text_field :name %>
<% unless tag_form.object.nil? || tag_form.object.new_record? %><%= tag_form.label :_delete, 'Remove:' %> <%= tag_form.check_box :_delete %>
<% end %> <% end %><%= post_form.submit "Save" %>
<% end %> ------------------------------------------------------- With these changes in place, you'll find that you can edit a post and its tags directly on the same view. NOTE: You may want to use javascript to dynamically add additional tags on a single form. For an example of this and other advanced techniques, see the link:http://github.com/alloy/complex-form-examples/tree/nested_attributes[nested model sample application]. == 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 link:http://guides.rubyonrails.org/[Ruby On Rails guides] * The link:http://groups.google.com/group/rubyonrails-talk[Ruby on Rails mailing list] * The #rubyonrails channel on irc.freenode.net * The link:http://wiki.rubyonrails.org/rails[Rails wiki] 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. == Changelog == http://rails.lighthouseapp.com/projects/16213-rails-guides/tickets/2[Lighthouse ticket] * February 1, 2009: Updated for Rails 2.3 by link:../authors.html#mgunderloy[Mike Gunderloy] * November 3, 2008: Formatting patch from Dave Rothlisberger * November 1, 2008: First approved version by link:../authors.html#mgunderloy[Mike Gunderloy] * October 16, 2008: Revised based on feedback from Pratik Naik by link:../authors.html#mgunderloy[Mike Gunderloy] (not yet approved for publication) * October 13, 2008: First complete draft by link:../authors.html#mgunderloy[Mike Gunderloy] (not yet approved for publication) * October 12, 2008: More detail, rearrangement, editing by link:../authors.html#mgunderloy[Mike Gunderloy] (not yet approved for publication) * September 8, 2008: initial version by James Miller (not yet approved for publication)