validate,class,define_method,exists?,[],array

http://api.rubyonrails.org/classes/ActiveRecord/Validations/ClassMethods.html#M001640
http://api.rubyonrails.org/classes/ActiveRecord/Base.html#M001701

<br /> class User < ActiveRecord::Base<br /> has_many :roles<br /> end<br /> class Role < ActiveRecord::Base<br /> TYPES = %w(admin editor writer guest)<br /> validates_inclusion_of :name, :in => TYPES<br /> <br /> #class << self 生成class method的scope, 裡面的method, 都會變成self.method_name<br /> class << self<br /> TYPES.each do |role_type|<br /> define_method "#{role_type}?" do<br /> roles.exists?(:name => role_type)<br /> end<br /> end<br /> end<br /> end<br />

Possible gotcha: You can‘t pass in a condition as a string e.g. "name = ‘Jamie’", this would be sanitized and then queried against the primary key column as "id = ‘name = \’Jamie"
<br /> Person.exists?(5)<br /> Person.exists?('5')<br /> Person.exists?(:name => "David")<br /> Person.exists?(['name LIKE ?', "%#{query}%"])<br />

原來這種要這樣設
<br /> # Get a role quickly by using: Role[:admin]<br />def self.[](name)<br /> self.find(:first, :conditions => ["name = ?", name.id2name])<br />end<br />

validate,before,create,define_method,callback

http://api.rubyonrails.org/classes/ActiveRecord/Callbacks.html#M001618
http://www.ruby-doc.org/core/classes/Module.html#M001682

* (-) save
* (-) valid
* (1) before_validation
* (2) before_validation_on_create
* (-) validate
* (-) validate_on_create
* (3) after_validation
* (4) after_validation_on_create
* (5) before_save
* (6) before_create
* (-) create
* (7) after_create
* (8) after_save

<br /> class CreditCard < ActiveRecord::Base<br /> # Strip everything but digits, so the user can specify "555 234 34" or<br /> # "5552-3434" or both will mean "55523434"<br /> def before_validation_on_create<br /> self.number = number.gsub(/[^0-9]/, "") if attribute_present?("number")<br /> end<br /> end<br /><br /> class Subscription < ActiveRecord::Base<br /> before_create :record_signup<br /><br /> private<br /> def record_signup<br /> self.signed_up_on = Date.today<br /> end<br /> end<br /><br /> class Firm < ActiveRecord::Base<br /> # Destroys the associated clients and people when the firm is destroyed<br /> before_destroy { |record| Person.destroy_all "firm_id = #{record.id}" }<br /> before_destroy { |record| Client.destroy_all "client_of = #{record.id}" }<br /> end<br />

---

define_method: 動態產生method 的好物
<br /> class ArticleVersion < ActiveRecord::Base<br /> STATES = { :edit => 'Edit',<br /> :edit_check => 'Edit Check',<br /> :sub_edit => 'Sub Edit',<br /> :publish_ready => 'Publish Ready',<br /> :published => 'Published' }<br /> STATES.each do |key, value|<br /> define_method "#{key}?", {<br /> self.state == "#{value}"<br /> }<br /> end<br /> end<br />

<br />#Defines an instance method in the receiver. The method parameter can be a Proc or Method object. If a block is specified, it is used as the method body. This block is evaluated using instance_eval, a point that is tricky to demonstrate because define_method is private. (This is why we resort to the send hack in this example.)<br /><br /> class A<br /> def fred<br /> puts "In Fred"<br /> end<br /> def create_method(name, &block)<br /> self.class.send(:define_method, name, &block)<br /> end<br /> define_method(:wilma) { puts "Charge it!" }<br /> end<br /> class B < A<br /> define_method(:barney, instance_method(:fred))<br /> end<br /> a = B.new<br /> a.barney<br /> a.wilma<br /> a.create_method(:betty) { p self }<br /> a.betty<br /><br />produces:<br /><br /> In Fred<br /> Charge it!<br /> #<B:0x401b39e8><br />