Intro to Ruby On Rails

1. Intro to Ruby On Rails Jon Walker

2. Ruby • Ruby is a reflective, object-oriented programming language • Syntax inspired by Perl with Smalltalk-like object-oriented features • Single-pass interpreted language • Created by Yukihiro "Matz" Matsumoto, first released in 1995 • Object-oriented • Every bit of data is an object, from integers to classes • Single inheritance with dynamic dispatch, mixins and singleton methods • Multi-paradigm programming language • Procedural: functions/variables outside classes are part of the root 'self' Object • Object orientation: everything is an object • Functional: anonymous functions, closures, and continuations • Introspection, reflection and meta-programming, threads • According to the Ruby FAQ • "If you like Perl, you will like Ruby and be right at home with its syntax. • If you like Smalltalk, you will like Ruby and be right at home with its semantics. • If you like Python, you may or may not be put off by the huge difference in design • philosophy between Python and Ruby."

3. Ruby on Rails • Ruby on Rails, often abbreviated RoR, or just Rails • open source web application framework written in Ruby • Closely follows the Model-View-Controller (MVC) architecture • Strives for • simplicity • Real-world applications in less code than other frameworks • A minimum of configuration – “convention over configuration” • What does that mean? • Ruby allows for extensive metaprogramming • Results in a syntax that many of its users find to be very readable • DHH • Ruby on Rails was extracted by David Heinemeier Hansson (DHH) • From his work on Basecamp • It was first released to the public in July 2004. • The current release is 1.2.1

4. Programming Language Book Trends

5. Ruby on Rails Shortcomings • Hidden complexity • l “Hitting the wall” when automagic stuff fails • Typical development: 10 minutes reading manual, 1 minute coding, • 10 minutes troubleshooting • Ruby is slow • its dynamic nature makes it difficult to compile at all • Need to use external libraries/processes for compute-intensive things • Does not interface well with existing database schemas • Either migrate data into new schema or make do with rough edges • Rails is single-threaded • Run multiple instances, but need to work around pitfalls

6. Agile Web Development with Rails, 2nd edition • Dave Thomas, Mike Clark and DHH • Reference “Rdoc” from api.rubyonrails.org • Programming Ruby • 1st edition available on the web • Ruby Tutorials • http://tryruby.hobix.com

7. DB Migrations • Transform the database class FixRestaurants < ActiveRecord::Migration def self.up rename_column(:restaurants, :adress, :address) end def self.down rename_column(:restaurants, :address, :adress) end End • Rake tasks (rake = ruby’s make) • Rake migrate – applies all new migrations to database • Rails stores the latest migration version in a schema_info table • Rake migrate VERSION=3 – applies migrations forwards or • backwards to arrive at migration 3

8. Model, View, Controller • What does this mean?

9. Design Pattern • A problem and its solution that occurs so frequently that there is a well established way to solve it • Model, View, Controller • Maybe the most common of these

10. Model / View / Controller • A web application is a good example. It has 3 parts: • The data model (model) • Mapping between relational database and objects • Ensuring that the data remains valid & consistent • May be used outside the web app • The business logic (controller) • Accepts a request, validates it, decides what happens next • Implements the core application logic • Fetches or calculates the data to be shown next • The presentation layer – generating HTML (or …) (view) • Produces the HTML mark-up from data provided by business logic • Often created by non-programmers (web designers)

11. Model / View / Controller (cont) • Generally … • Models • One model per database table • Use an explicit join table & model for many-to-many relationships • Views • One view per response • Often view uses several partials, reusable page fragments • Std scaffold creates 4 views + 1 partial per controller • Controllers • One per model, sometimes more • One per list/show/edit/search page-set • Scaffold demo • script/generate scaffold Bank

12. Rails Scaffolding: 7 Actions • Index/list • List all items • New • Display empty form for new item • Create • Create item based on “new” form • Show • Display item • Edit • Display item in form for editing • Update • Update item based on “edit” form • Destroy • Delete item

13. URLs, controllers, actions, IDs • Rails provides routes to map URLs to actions • From routes.rb: • # Install the default route as the lowest priority. • map.connect ':controller/:action/:id' • URLs are divided into parts by “/” • Query string or POST parameters • Parsed by default into params hash • http://host/restaurants/list?city=isla+vista&state=ca • params[:city] == “isla vista” • params[:state] == “ca”

14. Views – .rhtml / ERb • “Embed ruby into HTML” <% restaurant.ratings.each do |rating| %> <p><span class=“score”><%= h rating.score %></span> by <span class=“user”><%= h rating.user.nickname %></span> </p> <% end %> Restaurant.ratings.each do |rating| puts ‘<p><span class=“score”>’ puts h(rating.score) puts “</span>\nby\n<span class=\“user\”>” puts h(rating.user.nickname) puts “</span>\n</p>” end

15. View variables • Variables available in a view • When an action terminates, an auto-generated wrapper calls • render :file => “controller/action” • Unless the action called render explicitly • render is a method of the controller • => all controller instance variables are in scope • hence idioms such as: • @restaurant = Restaurant.find(params[:id])