Rails: MVC in action

Transcription

1 Ruby on Rails

2 Basic Facts 1. Rails is a web application framework built upon, and written in, the Ruby programming language. 2. Open source 3. Easy to learn; difficult to master. 4. Fun (and a time-saver)! 5. Utilizes a Model-View-Controller (MVC) architecture (more on that in a moment).

3 What is MVC MVC is the architecture pattern upon which Rails operates. a.k.a. observer design pattern It breaks down the web application into three distinct (but not necessarily discrete) entities: The models (objects) The views (visual interfaces) The controllers (communication between models and views)

4 Rails: MVC in action

5 MVC: Model Models are classes. They represent objects used by the Rails application. Model names are often linked directly to a table name in a database (line 1). Model is defined using ActiveRecord comment.erb

6 Rails: ActiveRecord Rails is a database-driven web application platform ActiveRecord bridges between SQL databases and classes Make database simple to use, as a ruby class. ActiveRecord translates the actions on an ActiveRecord class to actions on SQL database Provide cross-database support.

7 CRUB in SQL 4 basic operations on a table row: Create, Read, Update attributes, Destroy INSERT INTO students (last_name, wsu_sid, degree_expected) VALUES ( Fox, 99999, ), ( Bodik, 88888, ) SELECT * FROM students WHERE (degree_expected < ) UPDATE students SET degree_expected= WHERE last_name= Bodik ) DELETE FROM students WHERE wsu_sid=99999

8 SQL interpreted in ActiveRecord ActiveRecord, a major component of Rails... Uses SQL tables as underlying storage, and SQL commands as underlying manipulation, of collections of Ruby objects (Later) Provides an object-relationship graph abstraction using SQL Joins as the underlying machinery Oversimplification: 1 instance of Ruby class Foo == 1 row in a SQL table called Foos Let Rails do the work of creating our model and related stuff: script/generate scaffold student last_name:string first_name:string wsu_id:integer degree_expected:datetime

9 Scaffolding: jumpstart ActiveRecord identical app/models/student.rb create test/unit/student_test.rb create test/fixtures/students.yml create app/views/students/_form.rhtml create app/views/students/list.rhtml create app/views/students/show.rhtml create app/views/students/new.rhtml create app/views/students/edit.rhtml create app/controllers/students_controller.rb create test/functional/students_controller_test.rb create app/helpers/students_helper.rb create app/views/layouts/students.rhtml create public/stylesheets/scaffold.css For creating test cases CRUD on student views model & controller Capture common elements of student-related views

10 Database migrate: create table We re not done yet! Students table doesn t exist... Scaffolding generates a migration file 001_create_students.rb defining a class with first & last name, WSU ID, degree date To create the table, running: rake db:migrate Question: what database? config/database.yml

11 ActiveRecord SQL class CreateStudents<ActiveRecord::Migration def self.up create_table :students do tbl tbl.column :last_name, :string tbl.column :first_name, :string tbl.column :wsu_sid, :integer, :null=>false, :default=>9999 end end def self.down drop_table :students end end CREATE TABLE students ( id INT NOT NULL AUTO_INCREMENT, last_name VARCHAR(255), first_name VARCHAR(255), wsu_sid INT(11) DEFAULT 9999 );

12 ActiveRecord in nutshell A class library that provides an object-relational model over a plain old RDBMS Deal with objects & attributes rather than rows & columns SELECT result rows enumerable collection (later) object graph join query

13 MVC: Model Basic anatomy of a model:...validations for data used to populate the database (line 3)....associations with other models...user-defined instance methods (not shown). article.erb

14 MVC: View Views come in many flavors: *.html - Standard HTML *.erb - Embedded Ruby *.html.erb - HTML with Embedded Ruby _*.html.erb - A partial (note the leading underscore) *.json - JSON-encoded string representing one or more models Most views in a Rails application are called templates Templates should map directly to an associated controller action

15 MVC: View The actual user interface of the application. Used to display and interact with data from the database. Default file format: ERB (embedded Ruby) Automatically called after a controller action. A controller can explicitly call a different view using render, replacing the default page; or, redirect_to, redirecting the browser to a different URL.

16 MVC: View Index.html.erb

17 MVC: Controller Acts as an intermediary between the models and the views. Responds to user interactions from the user interface and performs operations on the models. Each action in a controller is [typically] linked to a default template in the Rails application. CRUD Create: New, Create; Read: Find, find_by_attributes Update: Save, update_attributes Delete: Destroy

18 MVC: Controller

19 Glue MVC together: routes Routes specify how a http request is routed. A route can be specified by: URL; HTML action: POST, GET, PATCH Routes are defined in config/routes.rb Routes are registered using helper functions; Routes.rb

20 Glue MVC together: routes Routes specify how a http request is routed. A route can be specified by: URL; HTML action: POST, GET, PATCH Routes are defined in config/routes.rb Routes are registered using helper functions; Routes.rb

21 Inspect routes Run command rake routes

22 Ruby on rails Features

23 View: Partials Templates to render parts of a view Helps promote reuse Filenames always start with an underscore Local variables can be passed to partials Simple to use: Step 1: create a _mypartial.html.erb containing reusable html/erb code; Step 2: in a html, call <%= render mypartial %>

24 View: Forms Used to submit data to controller to be saved Built based on models Use form helpers Form helpers function can access instance variables. Validate data before sending

25 View: Forms

26 Ruby on Rails Synergy with other tools

27 Haml HTML abstraction markup language Language for views Simplifies template creation Cleaner more readable code Example from haml.info

28 Devise Provided by gem Devise Handles login and sessions Include helpers like current_user Handle sessions transparently using cookies More information available at

29 Ruby on Rails resources Ruby on Rails guide: Hands-on example of building a blog. Rails for Zombie: