Rails 实现多对多自连接

1. 先生成关联代码

class WorkConnect < ActiveRecord::Base                          
  belongs_to :working, class_name: "Company"             
  belongs_to :worked, class_name: "Company"                                            
end                         

class Company < ActiveRecord::Base
  #working表示我合作的公司,worked表示跟我合作的公司
  has_many :working_c, class_name: "WorkConnect", foreign_key: :worked_id
  has_many :worked_c, class_name: "WorkConnect", foreign_key: :working_id
  has_many :working, class_name: "Company", through: :working_c
  has_many :worked, class_name: "Company", through: :worked_c
end     

2. 创建WorkConnect中两个字段

class CreateWorkConnect < ActiveRecord::Migration
  def change
    create_table :work_connects do |t|
      t.integer :worked_id
      t.integer :working_id
    end
  end
end

3. 然后进入console，调试，可以创建成功。

2.3.0 :003 > c1 = Company.find(2)
  Company Load (0.2ms)  SELECT  `companies`.* FROM `companies` WHERE `companies`.`id` = 2 LIMIT 1
 => #<Company id: 2, name: "Eastcompeace", created_at: "2016-03-21 04:50:28", updated_at: "2016-03-21 04:50:28", work_id: nil>
2.3.0 :004 > c2 = Company.find(5)
  Company Load (0.2ms)  SELECT  `companies`.* FROM `companies` WHERE `companies`.`id` = 5 LIMIT 1
 => #<Company id: 5, name: "360", created_at: "2016-03-21 06:53:37", updated_at: "2016-03-21 06:53:37", work_id: nil>
2.3.0 :005 > c1.working
  Company Load (0.4ms)  SELECT `companies`.* FROM `companies` INNER JOIN `works` ON `companies`.`id` = `works`.`working_id` WHERE `works`.`worked_id` = 2
 => #<ActiveRecord::Associations::CollectionProxy []>
2.3.0 :006 > c1.working << c2
   (0.2ms)  BEGIN
  SQL (0.3ms)  INSERT INTO `works` (`worked_id`, `working_id`) VALUES (2, 5)
   (67.9ms)  COMMIT
 => #<ActiveRecord::Associations::CollectionProxy [#<Company id: 5, name: "360", created_at: "2016-03-21 06:53:37", updated_at: "2016-03-21 06:53:37", work_id: nil>]>
2.3.0 :007 > c1.worked
  Company Load (0.5ms)  SELECT `companies`.* FROM `companies` INNER JOIN `works` ON `companies`.`id` = `works`.`worked_id` WHERE `works`.`working_id` = 2
 => #<ActiveRecord::Associations::CollectionProxy []>
2.3.0 :008 > c1.working
 => #<ActiveRecord::Associations::CollectionProxy [#<Company id: 5, name: "360", created_at: "2016-03-21 06:53:37", updated_at: "2016-03-21 06:53:37", work_id: nil>]>
2.3.0 :009 > c1.save
   (0.2ms)  BEGIN
   (0.1ms)  COMMIT
 => true
2.3.0 :010 > c2.worke
NoMethodError: undefined method `worke' for #<Company:0x00000003c33e00>
2.3.0 :011 > c2.worked
  Company Load (0.5ms)  SELECT `companies`.* FROM `companies` INNER JOIN `works` ON `companies`.`id` = `works`.`worked_id` WHERE `works`.`working_id` = 5
 => #<ActiveRecord::Associations::CollectionProxy [#<Company id: 3, name: "tengxun", created_at: "2016-03-21 05:56:22", updated_at: "2016-03-21 05:56:22", work_id: nil>, #<Company id: 2, name: "Eastcompeace", created_at: "2016-03-21 04:50:28", updated_at: "2016-03-21 04:50:28", work_id: nil>]>
2.3.0 :012 > c2.working
  Company Load (0.4ms)  SELECT `companies`.* FROM `companies` INNER JOIN `works` ON `companies`.`id` = `works`.`working_id` WHERE `works`.`worked_id` = 5
 => #<ActiveRecord::Associations::CollectionProxy []>

该例子纯属练习理解Model的关联，不考虑业务需求，欢迎指正。