模型层的写作风格以及through

# -*- coding: utf-8 -*-
class User < ActiveRecord::Base

  -----------------------------

  include Activity::UserMethods
end

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class Activity < ActiveRecord::Base

  attr_accessible :title, :content, :start_time, :end_time

  belongs_to :creator, :class_name => 'User', :foreign_key => :creator_id

  validates  :creator, :presence => true
  validates  :title,   :presence => true
  validates  :content, :presence => true

  validates :start_time, :end_time, :presence => true

  validate :validate_start_and_end_time

  def validate_start_and_end_time
    errors.add(:base,'开始时间必须早于结束时间') if self.start_time > self.end_time
  end

  module UserMethods
    def self.included(base)
      base.has_many :activities, :foreign_key => :creator_id
    end
  end

  include ActivityMembership::ActivityMethods

end

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class ActivityMembership < ActiveRecord::Base
  attr_accessible :activity, :user

  belongs_to :user
  belongs_to :activity, :foreign_key => :activity_id

  validates  :user,     :presence => true
  validates  :activity, :presence => true



  module ActivityMethods
    def self.included(base)
      base.send :include, InstanceMethods
      base.has_many :activity_memberships
      base.has_many :members, :through => :activity_memberships, :source => :user
    end

    module InstanceMethods
      def add_member(user)
        self.activity_memberships.create :user => user
      end

      def remove_member(user)
        self.activity_memberships.where(:user_id=>user.id).destroy_all
      end
    end
  end
end