Extending Rails with Plugins (2007)

tasks install.rb uninstall.rb test

Rails plugins can add anything

Rails plugins can change anything

Methods Adding with Ruby, and Rails

Modules module MineNotYours def copyright "(c) me" end end

Adding methods to instances... class SomeClass include MineNotYours end c = SomeClass.new c.copyright # => "(c) me"

... and so to Models class SomeModel < AR::Base include MineNotYours end m = SomeModel.find(:first) m.copyright # => "(c) me"

Adding methods to all models # Re-opening the target class # directly class ActiveRecord::Base include MineNotYours end

Adding methods to all models # Send the ‘include’ message to # our target class AR::Base.send(:include, MineNotYours)

Behaviour Adding as a part of Class Deﬁnitions

Plain Ol’ Ruby Objects class ConferenceDelegate attr_accessor :name end c = ConferenceDelegate.new c.name = "Joe Blogs" c.name # => "Joe Blogs"

Plain Ol’ Ruby Objects class ConferenceDelegate :name end c = ConferenceDelegate.new c.name = "Joe Blogs" c.name # => "Joe Blogs" attr_accessor

“Class” methods irb:> c.class.private_methods => ["abort", "alias_method", "at_exit", "attr", "attr_accessor", "attr_reader", "attr_writer", "binding", "block_given?", "define_method", "eval", "exec", "exit", "extended", "fail", "fork", "getc", "gets", "global_variables", "include", "included", "irb_binding", "lambda", "load", "local_variables", "private", "proc", "protected", "public", "puts", "raise", "remove_class_variable", "remove_const", "remove_instance_variable", "remove_method", "require", "sleep", "split", "sprintf", "srand", "sub", "sub!", "syscall", "system", "test", "throw", "undef_method", "untrace_var", "warn"]

Ruby Hacker; Know Thy-self class ConferenceDelegate attr_accessor :name end # self == ConferenceDelegate

Ruby Hacker; Know Thy-self class ConferenceDelegate def self.do_something “OK” end do_something end # => “OK”

Ruby Hacker; Know Thy-self class ConferenceDelegate def self.has_name attr_accessor :name end has_name end t = ConferenceDelegate.new t.name = “Joe Blogs”

Another module module Personable def has_person_attributes attr_accessor :first_name attr_accessor :last_name end end

Adding “class” methods class RubyGuru extend Personable end has_person_attributes g = RubyGuru.new g.first_name = “Dave” g.last_name = “Thomas”

Specifying Behaviour in Rails class SuperModel < ActiveRecord::Base validates_presence_of :rich_boyfriend validates_size_of :entourage, :minimum => 20 has_many :vices, :through => :boyfriends end class FootballersWife < ActiveRecord::Base validates_presence_of :rich_boyfriend validates_size_of :entourage, :minimum => 5 has_many :vices, :through => :boyfriends end

Bundling behaviour module ModelValidation def acts_as_glamourous(size) validates_presence_of :rich_boyfriend validates_size_of :entourage, :minimum => size has_many :vices, :through => :boyfriends end end # ... add this method to the target class ActiveRecord::Base.send(:extend, ModelValidation)

Our own ActiveRecord behaviour class Celebrity < AR::Base acts_as_glamourous(50) end

Class and instance behaviour module GlamourPlugin def acts_as_glamourous(size) validates_presence_of :rich_boyfriend # etc... end end

Class and instance behaviour module GlamourPlugin def acts_as_glamourous validates_presence_of :rich_boyfriend # etc... end module InstanceBehaviour def react_to(other_person) if other_person.is_a?(Paparazzo) other_person.destroy end end end end

Class and instance behaviour module GlamourPlugin def acts_as_glamourous validates_presence_of :rich_boyfriend # etc... include GlamourPlugin::InstanceBehaviour end module InstanceBehaviour def react_to(other_person) if other_person.is_a?(Paparazzo) other_person.destroy end end end end

Our plugin in action class Diva < ActiveRecord::Base acts_as_glamourous end dude = Paparazzo.create(:lens => "Huge") Paparazzo.count # => 1 starlet = Diva.new(:name => "Britney", :entourage => 873, :quirk => "No hair") starlet.react_to(dude) Paparazzo.count # => 0

changing the behaviour of existing classes

Changing existing behaviour # replacing implementation # via inheritance class Thing < Object def object_id @my_custom_value end end

Inheritance is not always possible ActiveRecord::Base ActionController::Base ActionView::Base Dependencies ActionMailer::Base Routing DispatchingAssociations ... and more...

changing the implementation of existing methods

Ruby classes are always open class ActiveRecord::Base def count execute("SELECT COUNT(*) FROM #{table_name}") / 2 end end

Aliasing methods class ActiveRecord::Base end alias_method :__count, :count def count __count / 2 end

Method chains with Rails class FunkyBass def play_it "Funky" end end bass = FunkyBass.new bass.play_it # => "Funky"

Method chains - new behaviour module Soul def play_it_with_soul "Smooth & " + play_it_without_soul end end

How alias_method_chain works class FunkyBass include Soul alias_method_chain :play_it, :soul end alias_method :play_it_without_soul, :play_it alias_method :play_it, :play_it_with_soul # underneath the hood:

Adding the new functionality class FunkyBass include Soul alias_method_chain :play_it, :soul end bass.play_it # => "Smooth & Funky"

Method chains in action class ActiveRecord::Base def count_with_fixes return count_without_fixes + 1 end alias_method_chain :count, :fixes end MyModel.count # calls new method

Patching Rails’ Dependencies class Dependencies def require_or_load(file_name) # load the file from the normal # places, i.e. $LOAD_PATH end end

New plugin-loading behaviour module LoadingFromPlugins # we want to replace Rails’ default loading # behaviour with this def require_or_load_with_plugins(file_name) if file_exists_in_plugin(file_name) load_file_from_plugin(file_name) else require_or_load_without_plugins(file_name) end end end

Injecting the new behaviour module LoadingFromPlugins def require_or_load_with_plugins(file_name) if file_exists_in_plugins(file_name) load_file_from_plugin(file_name) else require_or_load_without_plugins(file_name) end end end def self.included(base) base.send(:alias_method_chain, :require_or_load, :plugins) end Dependencies.send(:include, LoadingFromPlugins)

Extending Rails with Plugins (2007)

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