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 />