6.170 Tutorial 2 ­- Rails Basics

6.170 Tutorial 2 ­ Rails Basics Prerequisites 1. RoR Installed and “Hello World” app from P0 working. 2. Familiarity with “Separation of Concerns” and M­V­C Controller. 3. Some knowledge of databases is useful but not necessary. Goals of this Tutorial Get familiar with the some basics of development using Ruby on Rails. Tutorial Note: Read the README.rdoc file of your app. It has some very useful information for developing and debugging Rails apps. You’ll also find a lot of useful guides from http://guides.rubyonrails.org/index.html. You Must Have Already Figured: 1. What is Ruby on Rails? a. A framework for rapid web­based development using the Ruby language b. A community of passionate developers and contributors. 2. What features does it provide? a. Clean Separation of concerns: Model­View­Controller. b. Rapid web­based software development and testing. c. Rapid DB Access and Migrations ­ without knowing many details of databases. d. rake, a “make” system for Ruby for automating repetitive tasks. e. Excellent software testing tools ­ details will be covered in a future recitation. f. A vibrant community of developers and contributors who make life easy for you. 3. What is Heroku? What features does it provide? a. A cool hosting service for RoR apps ­ makes deploying and running complete RoR applications very easy. b. Is based on Amazon EC2 infrastructure; allows dynamic provisioning of web servers, and backend servers. 4. What is Git? GitHub? a. Git is an awesome source control system and GitHub is an online service for easy creation and sharing of Git repositories. Topic #0: Useful commands when developing rails applications “rails” command provides many useful scripts for auto code generation etc. Examples: $ rails [command] [args] “rake” is Ruby’s make system. Many useful development tasks come included as rake tasks Examples: $ rake -T $ rake db:setup; rake db:migrate; rake db:drop:all $ rake test; rake test:uncommitted Note: Many common tasks come built-in with rails but you can always develop custom rake tasks to automate your own work. Topic #1: Routing in Rails The material in this section is adapted from: http://guides.rubyonrails.org/routing.html Also see documentation in your routes.rb file Rails Router 1. Maps a URI to methods in controllers a. Example: post "home/login" => "home#login" 2. Utility methods for generating paths and URLs - no hard-coding of URLs 3. Routing specified in config/routes.rb config file Two kinds of Routing in Rails 1. Resourceful Routing: Shorthand for resources 2. Non-Resourceful Routing: For all other routing Resourceful Routing Examples At the command line in your app directory: $ rails generate resource book title:string author:string price:number Check config/routes.rb file for: resources :books This creates seven different routes in your application, all mapping to the Books controller: HTTP Verb Path action used for GET /books index display a list of all books GET /books/new new return an HTML form for creating a new books 2 POST /books create create a new book GET /books/:id show display a specific book GET /books/:id/edit edit return an HTML form for editing a book PUT /books/:id update update a specific book DELETE /books/:id destroy delete a specific book In your browser, go to http://localhost:3000/books/new You will see an error like : Unknown action The action 'new' could not be found for BooksController Now edit the app/controllers/book_controller.rb file so that it looks like: class BooksController Now http://localhost:3000/books and http://localhost:3000/books/new will work. Similarly, other action methods like show update, edit destroy can be defined on Books controller and corresponding view files written. Notice in this example: 1. :render directive and its parameters 2. Rendering of appropriate view even when :render is not specified in “new” method 3. Dynamic content in view files and variable scope + visibility between controllers and views Examples of Non­Resourceful Routing ## Static routes post /home/login => “home#login” post /library/catalog/update => “library/catalog#update” get /home/index ## Examples of routes with dynamic segments match ":controller/" => ":controller#index" http://localhost:3000/books will map to BooksController.index match ":controller/:action" http://localhost:3000/books/deleteall will map to BooksController.deleteall Warning: This route will match every method in every controller. Use cautiously. match ":controller/:action/:user_id" http://localhost:3000/books/checkout/10 will map to BooksController.checkout with params[:user_id] = 10 4 Note: You can mix static and dynamic segments in the match directive. Helper Methods for Routing in Controllers and Views resource_path, resource_url. For resource :books ● books_path returns /books ● new_book_path returns /books/new ● edit_book_path(:id) returns /books/:id/edit (for instance, edit_book_path(10) returns /books/10/edit) ● book_path(:id) returns /books/:id (for instance, book_path(10) returns /books/10) Each of these helpers has a corresponding _url helper (such as books_url) which returns the same path prefixed with the current host, port and path prefix. Inspecting and Testing Routes $ rake routes More Routing Concepts Namespaces in Resourceful Routing You can define namespaces for each of your resources as shown below: namespace :admin do resources :posts, :comments end Nested Resources See http://guides.rubyonrails.org/routing.html#nested-resources URL Redirection Using Routes See http://guides.rubyonrails.org/routing.html Route Globbing match 'books/*other' => 'books#unknown' This route would match “books/12” or “/books/long/path/to/12”, setting params[:other] to "12" or "long/path/to/12". Topic #2: Views and Client Side Assets Also see: http://guides.rubyonrails.org/layouts_and_rendering.html We will use “erb” format for dynamic views. You are welcome to use and experiment with other 5 view technologies like HAML and choose the one which suits you best. But not all TAs may not be able to help you if you encounter problems - only one of the TAs uses HAML regularly. View Basics Dynamic content specified in erb files via 1. Each view can have a layout template, including no layout. 2. Typically used to create a template for header and footer of pages - then each view focuses on only its part 3. Layouts are in app/views/layouts; Default layout is “application.html.erb” 4. Include your views usingdirective in layout 5. Controller wide layouts possible. 6. render directive also can take a layout parameter a. render “new”, :layout => :home_page b. render “new”, :layout => false View Partials 7 Including repeated HTML code Client Side Assets Details of CSS, Javascript, and other client side assets will be covered in a later recitation. Topic #3: Controllers Controllers help isolate presentation layer from the data layer - separation of concerns Using this - you can use the same code to develop a web based app, a mobile based app, or a some other view technology without changing much of the underlying code. Similarly you can use any data store - relational databases, flat files, etc. and switch between them without changing any of the view code. Default/Base Controller: ApplicationController (application_controller.rb) New controllers are created using: ## This will use “app/views/layouts/book_layouts.html.erb” as the ## layout for all views in this controller, unless overriden in a ## method. layout :book_layout def index render "index", :layout => false end def new @time_now = Time.now ## render "new", :layout => false end end You can start adding new methods which will perform actions. For example: def checkout ## This is pseudo code @book = Book.find(params[:book_id]) if (@book.available?) @book.checkout(params[:user_id]) 8 else end msg = “Book checked out” msg = “Book not available for checkout” end render “checkout”, :layout => false Some useful objects available to you in the controllers are: params: A hash of HTTP params which came with the request. request: The HTTP request object as a hash session: The session object as a hash Some useful directives in controllers: render “view”, :layout => [layout_name | false] render :nothing => true ## Useful for async actions for which you do not need ack redirect_to “/relative/path/to/view” Note: Any instance variables that you require in the view must be set up in the current action before calling render. Topic #4: Data Access in Rails (“Model” part of MVC) http://guides.rubyonrails.org/active_record_querying.html http://guides.rubyonrails.org/migrations.html ActiveRecord is a data interface/access layer: allows you to store/retrieve/query a database without having to learn and worry about SQL. All you need to know is the corresponding model class in ruby and rails takes care of the SQL level details of interaction with the database! Generating a Model $ rails generate model library name:string address:string $ invoke active_record $ create db/migrate/20130211132022_create_libraries.rb $ create app/models/library.rb $ invoke test_unit 9 $ $ create create test/unit/library_test.rb test/fixtures/libraries.yml This command generate the model class (app/models/library.rb), a migration script to create the corresponding table in the database (db/migrate/xxx_create_libraries.rb), and some files to run tests. Note: 1. Library class extends from ActiveRecord::Base which provides many utility methods for interacting with Model objects. (as you will see) 2. attr_accessible directive specifies the accessible attributes of the model via getters and setters, i.e. “library.name”, “library.address” can be used on the LHS or RHS of an assignment expression. 3. Many more useful directives available. db/migrate/20130211132022_create_libraries.rb: create_table :libraries do |t| t.string :name t.string :address t.timestamps end end end Note: 1. This migration script creates the database table. 2. Automatically adds an “id” field to the model (not shown) and a timestamps field to hold the last updated timestamp for each record. Creating the Database Table $ rake db:migrate 10 Simple operations on the Library model You can now start using this model in your code. Examples are shown below: ## Return a library object with id 10 @library = Library.find(10) ## Create a new library object and save it to the database lib = Library.new({:name => “Hayden”, :address => “100 Memorial Drive”}) lib.save() ## Retrieve a library object with name = “Hayden” library = Library.find_by_name(“Hayden”) More Fun Details of the Model Enforcing Referential Constraints: In Book class: belongs_to :library In Library class: has_many :books Retrieving multiple objects: Use Model.xxx where xxx = where, select, group, having, order, limit, join, order Topic #5: Some Useful Rails Configuration Files 1. boot.rb, application.rb, environment.rb 2. database.yml Topic #6: Debugging Rails Apps Which IDE should use for development? Your TAs are familiar with the following: ● Sublime + Vi editor with command line ● Emacs Editor with command line ● RubyMine (30 day trial) Others have used ● Aptana RadRails Next Tutorialp Details of the Ruby programming language 12