Concerning 'Application'

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Concerning ‘Applications’ Kyosuke MOROHASHI (@moro) RubyKaigi 2013, May 31, 2013

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ॾڮګհ(@moro) Kyosuke MOROHASHI

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31st on leaderboard

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Background

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Rails applications are applied to complex real-life problems.

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Many rails users worry about the ‘Fat model’ problem.

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✓ One of solutions is the technique of ‘Concern’s, which divides model behavior into small units. ✓ implemented as ActiveSupport::Concern

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What is Rails’ ActiveSupport:: Concern ?

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Ruby’s Module extension by Rails

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✓ automatically extends own ClassMethods module if exists. ✓ provides included {} callback for declarative methods.

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gist:moro/5652724 module Censorable extend ActiveSupport::Concern included do has_many :monitor_requests, as: :entity, validates :censor_status, inclusion: Censorable end module ClassMethods def censor_passed where(status: Censorable::PASSED_STATUSES) end end def censor_passed? censor_status.passed? end

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What’s nice about ActiveSupport::Concern ?

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✓ Provides a convention to write: ✓ Instance methods ✓ Class methods ✓ Conﬁguration & customization by declarative methods.

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became ﬁrst class citizen in Rails 4 <3 <3 <3

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ActiveSupport:: Concern is a nice Rails’ module extension.

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What should we Concern about?

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Models’ common behaviors

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✓ Users can tag the {question|answer}. ✓ Users can comment on the {question|answer}. ✓ Service providers must censor user- posted {question|answer}’s content.

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class Question < AR::Base include Taggable include Commentable include Censorable # and question specific definitions.. end class Answer < AR::Base include Taggable include Commentable include Censorable # and question answer definitions.. end

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Nested resource's parent.

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# question and answers that the user has # /users/:user_id/questions # /users/:user_id/answers resources :users do resources :questions resources :answers end

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module UsersResource extend ActiveSupport::Concern included do helper_method :owner hide_action :owner end private def owner @_owner ||= User.where(id: params[:user_id]).first end end

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use AS::Concern to extract common behaviors.

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How do we use AS::Concern nicely?

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Keep it a GLUE

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✓ Add only a few methods to a base class. ✓ Keep ‘Loose Coupling’ between Concern and models.

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gist:moro/5652724 module Censorable extend ActiveSupport::Concern (skip) def feedback_monitor_judge(status) if PASSED_STATUSES.include?(status) .... else .... end end def request_monitoring! req = monitor_requests.create!(content: monitor res = post_monitor_request(req) unless res.code == '200' raise Censorable::MonitorRequestFailed.new(re end Bad case

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gist:moro/5652724 module Censorable extend ActiveSupport::Concern (skip) def request_monitoring! MonitorRequest.submit(self) end end Good case

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gist:moro/5652724 class MonitorRequest < ActiveRecord::Base class << self def submit(entity) req = create!(entity: entity, content: monito res = post_monitor_request(req) unless res.code == '200' raise Censorable::MonitorRequestFailed.new( end end end end Good case

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Tests become more obvious.

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gist:moro/5652724 describe Censorable do let(:question) { create(:question) } before do question.request_monitoring! end specify do MonitoringRequest. should have(1).record end end Bad case

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gist:moro/5652724 describe MonitoringRequest do let(:question) { create(:question) } before do MonitoringRequest.submit(question) end specify do MonitoringRequest. should have(1).record end end Good case

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How to glue class speciﬁc behavior?

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✓ Plain old conditional branch ✓ Template methods

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gist:moro/5652724 class MonitorRequest < ActiveRecord::Base class << self def monitoring_content(obj) case obj when Question [obj.title, obj.body].join("\n\n") when Answer entity.body end end end end Plain old conditional branch

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PROS: Less effect on base class. CONS: Too naive. Plain old conditional branch

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gist:moro/5652724 class MonitorRequest < ActiveRecord::Base class << self def submit(entity) content = entity.monitoring_content ... class Question < AR::Base def monitoring_content [title, body].join("\n\n") end end class Answer < AR::Base def monitoring_content; body; end end Template method

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PROS: Acquires polymorphism. CONS: pollutes base classes. Template method

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Keep Concern a thin, glue layer. But still something is wrong with interface with base class...

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in Ruby 2.0 Concern meets Refinements

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“Reﬁnements are intended to restrict the impact of monkey patching to a certain scope http://jp.rubyist.net/magazine/?Ruby200SpecialEn-refinement @shugomaeda says:

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Restrict the impact of glue code’s template method.

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gist:moro/5652724 module Censorable module MonitoringContent refine Question do def monitoring_content [title, body].join("\n\n") end end refine Answer do def monitoring_content; body ; end end end end Reﬁnements

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gist:moro/5652724 using Censorable::MonitoringContent class MonitorRequest < ActiveRecord::Base class << self def submit(entity) content = entity.monitoring_content ... Reﬁnements

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BTY: Concern as a service layer glue? ✓ Refinements let us define: ✓ context specific extensions. ✓ multi-classes ext. in one place.

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BTY: Concern as a service layer glue? ✓ Concern could: ✓ provide namespace to the extensions. ✓ glue base classes and the extensions.

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Ruby 2.0’s reﬁnements are so great that we can extract concerns nicely with them.

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Wrapping up

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✓ AS::Concern is a way to keep your application clean. ✓ I talked about a way to use it nicely :-)

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ActiveSupport::Concern is not ‘off the Rails’.

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It’s a supporter, like a bicycle: it helps your journey where there's no common rails.

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Acknowledgements ✓ All of Ruby community: especially Ruby team , Rails team, RubyKaigi staffs and you. ✓ My clients, colleagues, friends and family. ✓ Nice material authors: ✓ http://good-wallpapers.com/misc/22337 ✓ http://www.fontspace.com/pete-klassen/ringbearer ✓ http://subtlepatterns.com/ ✓ http://www.flickr.com/photos/dailyinvention/23126614/ ✓ http://www.flickr.com/photos/bdamgaard/510134092/