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Object Oriented Design An Introduction to Beautiful Code Design Tuesday, November 6, 12

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Hello World @styliii styliii.com github.com/styliii Tuesday, November 6, 12

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Procedural Code collect data parse data if name is Li if name is not Li puts “Hi Li” puts “Bye” Tuesday, November 6, 12

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Procedural Code Tuesday, November 6, 12

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Procedural Code Data f1(x) f4(x) f3(x) f2(x) Tuesday, November 6, 12

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Procedural Code Data f1(x) f4(x) f3(x) f2(x) Tuesday, November 6, 12

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Procedural Code Data f1(x) f4(x) f3(x) f2(x) f5(x) Tuesday, November 6, 12

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Procedural Code Data f1(x) f4(x) f3(x) f2(x) Tuesday, November 6, 12

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Procedural Code Data f1(x) f4(x) f3(x) f2(x) Tuesday, November 6, 12

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Procedural Code Data f1(x) f4(x) f3(x) f2(x) new f5(x) Tuesday, November 6, 12

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Object Oriented Code f1(x) f4(x) f3(x) f2(x) Data Tuesday, November 6, 12

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Object Oriented Code f1(x) f4(x) f3(x) f2(x) Tuesday, November 6, 12

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Object Oriented Code f1(x) f4(x) f3(x) f2(x) Tuesday, November 6, 12

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Object Oriented Code Tuesday, November 6, 12

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History: Gang of Four Tuesday, November 6, 12

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Change Tuesday, November 6, 12

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Unhealthy Code rigid fragile - distant and seemingly unrelated code breaks after ever change immobility - code hopelessly entangled, you can’t reuse viscous - behaving badly is the most attractive alternative Tuesday, November 6, 12

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Dependencies “Dependency will kill your code. Design will save it.” Tuesday, November 6, 12

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SOLID Principles Single Responsibility Open/Closed Liskov Substitution Interface Segregation Dependency Inversion Tuesday, November 6, 12

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Single Responsibility A class should have one, and only one, reason to change. Tuesday, November 6, 12

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Open/Closed Software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification. Tuesday, November 6, 12

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Liskov Substitution Objects in a program should be replaceable with instances of their subtypes without altering the correctness of that program. Tuesday, November 6, 12

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Interface Segregation Many client specific interfaces are better than one general purpose interface. Tuesday, November 6, 12

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Dependency Inversion Depend upon abstractions. Do not depend upon concretions. Tuesday, November 6, 12

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Dependency Inversion SOLID Single Responsibility Open/Closed Liskov Substitution Interface Segregation Tuesday, November 6, 12

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Dependency Inversion SOLID Single Responsibility Open/Closed Tuesday, November 6, 12

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Let’s Code! Tuesday, November 6, 12

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Let’s Code! require 'sqlite3' class Employer attr_accessor :name, :url, :about @@db ||= SQLite3::Database.new('jobs.db') @@db.results_as_hash = true def initialize(name="", url="", about="") @name = name @url = url @about = about end def insert_employer @@db.execute("INSERT INTO employers (name, url, about) VALUES (?, ?, ?)", [@name, @url, @about]) end Tuesday, November 6, 12

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SRP in Play require 'sqlite3' class Employer attr_accessor :name, :url, :about def initialize(name="", url="", about="") @name = name @url = url @about = about end end class Database @@db ||= SQLite3::Database.new('jobs.db') @@db.results_as_hash = true def insert_employer @@db.execute("INSERT INTO employers (name, url, about) VALUES (?, ?, ?)", [@name, @url, @about]) end end Tuesday, November 6, 12

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Make Database Class Work class Database @@db ||= SQLite3::Database.new('jobs.db') @@db.results_as_hash = true def insert_employer @@db.execute("INSERT INTO employers (name, url, about) VALUES (?, ?, ?)", [@name, @url, @about]) end end Tuesday, November 6, 12

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Make Database Class Work class Database @@db ||= SQLite3::Database.new('jobs.db') @@db.results_as_hash = true def insert_employer @@db.execute("INSERT INTO employers (name, url, about) VALUES (?, ?, ?)", [@name, @url, @about]) end end class Database attr_accessor :connection def initialize @connection = SQLite3::Database.new('jobs.db') self.connection.results_as_hash = true end def insert_employer self.connection.execute("INSERT INTO employers (name, url, about) VALUES (?, ?, ?)", [@name, @url, @about]) end end Tuesday, November 6, 12

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Abstract the Employer leftovers class Database attr_accessor :connection def initialize @connection = SQLite3::Database.new('jobs.db') self.connection.results_as_hash = true end def insert_employer self.connection.execute("INSERT INTO employers (name, url, about) VALUES (?, ?, ?)", [@name, @url, @about]) end end Tuesday, November 6, 12

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Abstract the Employer leftovers class Database attr_accessor :connection def initialize @connection = SQLite3::Database.new('jobs.db') self.connection.results_as_hash = true end def insert_employer self.connection.execute("INSERT INTO employers (name, url, about) VALUES (?, ?, ?)", [@name, @url, @about]) end end def insert_record(table, attribute_names, attributes) question_marks = Array.new(attribute_names.size, "?").join(", ") self.connection.execute("INSERT INTO #{table} (#{attribute_names.join(", ")}) VALUES (#{question_marks})", [attributes]) end Same As Tuesday, November 6, 12

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class Employer attr_accessor :name, :url, :about def initialize(name="", url="", about="") @name = name @url = url @about = about end end Our Employer Class Tuesday, November 6, 12

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Objects Interacting class Employer attr_accessor :name, :url, :about def initialize(name="", url="", about="") @name = name @url = url @about = about end end Tuesday, November 6, 12

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Objects Interacting class Employer attr_accessor :name, :url, :about def initialize(name="", url="", about="") @name = name @url = url @about = about end end def save Database.new.insert_record(table, attribute_names, attributes) end Tuesday, November 6, 12

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Objects Interacting class Employer attr_accessor :name, :url, :about def initialize(name="", url="", about="") @name = name @url = url @about = about end end def self.table @@table ||= "employers" end def save Database.new.insert_record(table, attribute_names, attributes) end Tuesday, November 6, 12

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Implement Save class Employer attr_accessor :name, :url, :about def initialize(name="", url="", about="") @name = name @url = url @about = about end end def self.table @@table ||= "employers" end def save Database.new.insert_record( table, attribute_names, attributes) end Tuesday, November 6, 12

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Implement Save class Employer attr_accessor :name, :url, :about def initialize(name="", url="", about="") @name = name @url = url @about = about end end def self.table @@table ||= "employers" end def save Database.new.insert_record( table, attribute_names, attributes) end self.class. Tuesday, November 6, 12

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Hardcode First class Employer attr_accessor :name, :url, :about def initialize(name="", url="", about="") @name = name @url = url @about = about end end def self.table @@table ||= "employers" end def save Database.new.insert_record( table, attribute_names, attributes) end self.class. Tuesday, November 6, 12

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Hardcode First class Employer attr_accessor :name, :url, :about def initialize(name="", url="", about="") @name = name @url = url @about = about end end def self.table @@table ||= "employers" end def save Database.new.insert_record( table, attribute_names, attributes) end self.class. attribute_names = ["name", "url", "about"] attributes = [self.name, self.url, self.about] Tuesday, November 6, 12

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Generalize Attributes class Employer attr_accessor :name, :url, :about end def self.table @@table ||= "employers" end def save attribute_names = self.instance_variables.map do |var| var.to_s.sub("@", "") end attributes = attribute_names.map do |att_name| self.send(att_name.to_sym) end Database.new.insert_record(self.class.table, attribute_names, attributes) end Tuesday, November 6, 12

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SRP for Methods too! class Employer def self.table @@table ||= "employers" end def save Database.new.insert_record(self.class.table, self.attribute_names, self.attributes) end def attribute_names self.instance_variables.map do |var| var.to_s.sub("@", "") end end def attributes attribute_names.map do |att_name| self.send(att_name.to_sym) end end end Tuesday, November 6, 12

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SRP for the Class require 'sqlite3' class Employer attr_accessor :name, :url, :about def initialize(name="", url="", about="") @name = name @url = url @about = about end def self.table @@table ||= "employers" end def save Database.new.insert_record(self.class.table, self.attribute_names, self.attributes) end end Tuesday, November 6, 12

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Modules module Attributable def attribute_names self.instance_variables.map do |var| var.to_s.sub("@", "") end end def attributes attribute_names.map do |att_name| self.send(att_name.to_sym) end end end Tuesday, November 6, 12

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Including the Module require 'sqlite3' require 'module' class Employer include Attributable attr_accessor :name, :url, :about def initialize(name="", url="", about="") @name = name @url = url @about = about end def self.table @@table ||= "employers" end def save Database.new.insert_record(self.class.table, self.attribute_names, self.attributes) end end Tuesday, November 6, 12

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What else? require 'sqlite3' require 'module' class Employer include Attributable attr_accessor :name, :url, :about def initialize(name="", url="", about="") @name = name @url = url @about = about end def self.table @@table ||= "employers" end def save Database.new.insert_record(self.class.table, self.attribute_names, self.attributes) end end Tuesday, November 6, 12

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Adding onto Module module Attributable def attribute_names self.instance_variables.map do |var| var.to_s.sub("@", "") end end def attributes attribute_names.map do |att_name| self.send(att_name.to_sym) end end end module Persistable def save Database.new.insert_record(self.class.table, self.attribute_names, self.attributes) end end Tuesday, November 6, 12

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Anything Else? require 'sqlite3' require 'module.rb' class Employer include Attributable, Persistable attr_accessor :name, :url, :about def initialize(name="", url="", about="") @name = name @url = url @about = about end def self.table @@table ||= "employers" end end Tuesday, November 6, 12

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Don’t Depend on Concretion Tuesday, November 6, 12

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Don’t Depend on Concretion class Employer attr_accessor :name, :url, :about def initialize(name="", url="", about="") @name = name @url = url @about = about end end Tuesday, November 6, 12

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Don’t Depend on Concretion class Employer attr_accessor :name, :url, :about def initialize(name="", url="", about="") @name = name @url = url @about = about end end def initialize(args={}) args.each do |key, value| self.send("#{key.to_sym}=", value) end end Same As Tuesday, November 6, 12

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Great Job :) require 'sqlite3' require 'module' class Employer include Attributable, Persistable attr_accessor :name, :url, :about def initialize(args = {}) args.each do |key, value| self.send("#{key.to_sym}=", value) end end def self.table @@table ||= "employers" end end Tuesday, November 6, 12

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SOLID Principles Single Responsibility Open/Closed Liskov Substitution Interface Segregation Dependency Inversion Tuesday, November 6, 12

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Resources Sandi Metz’s presentation on SOLID: http:/ /t.co/YqMiX7bq Diff between OO and Procedural Code: http:/ /www.youtube.com/watch? v=D8jZ0l_GwXQ Practical Object - Oriented Design in Ruby by Sandi Metz Source Code: https:/ /github.com/kcurtin/scrape_source https:/ /github.com/styliii/RubyJobScraper.git Books: Practical Object-Oriented Design in Ruby: An Agile Primer by Sandi Metz Pictures: http:/ /www.flickr.com/photos/yubacollege/4402710242/sizes/l/ http:/ /www.flickr.com/photos/dunechaser/6042984689/ http:/ /www.flickr.com/photos/ashclements/62704073/sizes/z/ Tuesday, November 6, 12