ActiveRecord::Associations::ClassMethods

Associations are a set of macro-like class methods for tying objects together through foreign keys. They express relationships like “Project has one Project Manager” or “Project belongs to a Portfolio”. Each macro adds a number of methods to the class which are specialized according to the collection or association symbol and the options hash. It works much the same way as Ruby's own attr* methods.

class Project < ActiveRecord::Base
  belongs_to              :portfolio
  has_one                 :project_manager
  has_many                :milestones
  has_and_belongs_to_many :categories
end

The project class now has the following methods (and more) to ease the traversal and manipulation of its relationships:登录查看完整内容