Learning Ruby's Dynamism with Rails

* Class-exp with AR
* include and extend with AS::Concern
* Standard Callbacks

Transcript

1. Learning Ruby's Dynamism
   with Rails
   @wtnabe
   Kanazawa.rb meetup #15
   2013-11-23 (Sat) at IT Plaza Musashi
   

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2. Topics
   

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3. Class-exp with AR
   include and extend with AS::Concern
   Standard Callbacks
   

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4. Class-exp with
   ActiveRecord
   

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5. ActiveRecord example
   class Book < ActiveRecord::Base
   belongs_to :bookstand
   validates :name, :presence => true
   scope :done, -> {where(:done => true)}
   def recent?
   published_at >= 1.year.ago
   end
   end
   

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6. ActiveRecord Pattern
   Class has table and ER definition
   Instance has DB record and relative
   methods
   

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7. Just another OOPL
   class Book extends ActiveRecord\Model {
   static $belongs_to = array(
   array('bookstand')
   );
   static $validates_presence_of = array(
   array('name')
   );
   public static function done() {}
   public function is_recent() {}
   }
   

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8. class Book < ActiveRecord::Base
   belongs_to :bookstand
   validates :name, :presence => true
   scope :done, -> {where(:done => true)}
   def recent?
   published_at >= 1.year.ago
   end
   end
   

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9. class Book < ActiveRecord::Base
   # class method call
   belongs_to :bookstand
   # class method call
   validates :name, :presence => true
   # class method call
   scope :done, -> {where(:done => true)}
   # instance method definition
   def recent?
   published_at >= 1.year.ago
   end
   end
   

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10. Ruby's Class
    Class is expression
    class keyword changes context
    It runs all
    class methods callable in class context
    

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11. include and extend with
    ActiveSupport::Concern
    

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12. new Rails 4 app.
    app
    ├── assets
    │ ├── images
    │ ├── javascripts
    │ └── stylesheets
    ├── controllers
    │ └── concerns <-- what ?
    ├── helpers
    ├── mailers
    ├── models
    │ └── concerns <-- what ?
    └── views
    └── layouts
    

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13. ActiveSupport::Concern
    Actually added from ActiveSupport 3.0
    

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14. What does it do ?
    include & extend
    

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15. include
    module ModA
    def methodA; p 'methodA'; end
    end
    class KlassA
    include ModA
    end
    KlassA.new.methodA # => "methodA"
    

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16. extend
    module ModB
    def methodB; p 'methodB'; end
    end
    class KlassB
    extend ModB
    end
    KlassB.methodB # => "methodB"
    

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17. Concern
    module M
    extend ActiveSupport::Concern
    included do
    scope :foo, :conditions => {:created_at => nil}
    end
    module ClassMethods
    def cm; puts 'I am a class method'; end
    end
    module InstanceMethods
    def im; puts 'I am an instance method'; end
    end
    end
    

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18. When to use
    class ModelA < ActiveRecord::Base
    include M
    end
    class ModelB < ActiveRecord::Base
    include M
    end
    treat common attributes with multi-models
    

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19. ActiveRecord
    call class methods
    define class methods
    define instance methods
    

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20. class Book < ActiveRecord::Base
    # call class methods
    belongs_to :bookstand
    validates :name, :presence => true
    scope :done, -> {where(:done => true)}
    # define class methods
    class << self
    def recent
    self.where(:published_ad >= 1.year.ago)
    end
    end
    # define instance methods
    def recent?
    published_at >= 1.year.ago
    end
    end
    

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21. ActiveSupport::Concern
    module M
    included do
    # call class methods
    end
    module ClassMethods
    ...
    end
    module InstanceMethods
    ...
    end
    end
    

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22. AS::Concern is
    a AR's best friend
    cf. https://www.ruby-lang.org/
    

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23. Standard Callbacks
    

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24. Rails Callback Examples
    before_validation
    after_save
    before_action ( before_filter )
    called Filter, but Callback internally
    

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25. How to use
    class Controller < ApplicationController
    before_action :auth,
    :unless => :logged_in?
    end
    class Model < ActiveRecord::Base
    before_validation do
    normalize_attributes
    end
    end
    ※ :unless keyword is allowed from ActiveSupport::Callbacks 4.0
    

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26. Ruby has many Callbacks
    

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27. Module.private_methods.sort.grep(/ed\z/)
    # =>
    [:inherited, :included, :extended,
    :prepended, :method_added,
    :method_removed, :method_undefined,
    :protected, :singleton_method_added,
    :singleton_method_removed,
    :singleton_method_undefined]
    

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28. Object#initialize, Object#method_messing,
    Module#append_features, ...
    append_features is called before execute include
    

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29. ex1) extended
    module M
    extend ActiveSupport::Concern
    end
    module ActiveSupport
    module Concern
    def self.extended(base)
    ...
    end
    end
    end
    

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30. ex2) inherited
    class Klass
    def self.inherited(name)
    raise StandardError,
    "#{name} cannot inherit #{self}"
    end
    end
    

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31. Similar to Final keyword
    class Subklass < Klass; end
    # => ...:3:in `inherited':
    # Subklass cannot inherit Klass (StandardE
    

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32. Conclusion
    

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33. Ruby is Dynamic !
    Class is expression
    Class can be modified easily with
    AS::Concern
    Useful Standard Callbacks
    

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34. Rails uses Ruby's dynamism
    very well
    

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35. Enjoy Rails & Ruby !
    

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