ruby-on-rails – 使用includes语句,Rails 4 has_and_belongs_to_many无法正常工作

最近我遇到了rails 4和HABTM关系的神秘错误.
首先是我的Gemfile：

source 'https://rubygems.org'
gem 'rails','~> 4.1.6'
gem 'pg'

下一个.我的模特：

class User < ActiveRecord::Base
end

class Teacher < User
  has_and_belongs_to_many :resources,foreign_key: :user_id
end

class Resource < ActiveRecord::Base
  has_and_belongs_to_many :teachers,association_foreign_key: :user_id
end

原始数据库数据：

select * from resources;
 id |         created_at         |         updated_at
----+----------------------------+----------------------------
  1 | 2014-10-13 08:24:07.308361 | 2014-10-13 08:24:07.308361
  2 | 2014-10-13 08:24:07.889907 | 2014-10-13 08:24:08.156898
  3 | 2014-10-13 08:24:08.68579  | 2014-10-13 08:24:08.884731
  4 | 2014-10-13 08:24:09.997244 | 2014-10-13 08:24:10.205753
(4 rows)

select * from users;
 id |         created_at         |         updated_at         |  type
----+----------------------------+----------------------------+---------
 13 | 2014-10-13 08:24:01.086192 | 2014-10-13 08:24:01.086192 | Teacher
 12 | 2014-10-13 08:24:00.984957 | 2014-10-13 08:24:00.984957 | Teacher
  2 | 2014-10-13 08:23:59.950349 | 2014-10-16 08:46:02.531245 | Teacher
(3 rows)

select * from resources_users;
 user_id | resource_id
---------+-------------
      13 |           1
       2 |           2
      12 |           3
       2 |           4
(4 rows)

最后这个bug：

➜  rails_test  bundle exec rails c
Loading development environment (Rails 4.1.6)
2.1.2 :001 > Resource.all.includes(:teachers).map(&:teachers).map(&:to_a)
  Resource Load (0.6ms)  SELECT "resources".* FROM "resources"
  sql (1.3ms)  SELECT "resources_users".*,"resources_users"."user_id" AS t0_r0,"resources_users"."resource_id" AS t0_r1,"users"."id" AS t1_r0,"users"."created_at" AS t1_r1,"users"."updated_at" AS t1_r2,"users"."type" AS t1_r3 FROM "resources_users" LEFT OUTER JOIN "users" ON "users"."id" = "resources_users"."user_id" AND "users"."type" IN ('Teacher') WHERE "users"."type" IN ('Teacher') AND "resources_users"."resource_id" IN (1,2,3,4)
 => [
[#<Teacher id: 13,created_at: "2014-10-13 08:24:01",updated_at: "2014-10-13 08:24:01",type: "Teacher">],[],[]]

正如您所看到的,只有第一批教师返回收藏中.但是Rails生成的sql是正确的并返回所有数据：

SELECT "resources_users".*,4);
 user_id | resource_id | t0_r0 | t0_r1 | t1_r0 |           t1_r1            |           t1_r2            |  t1_r3
---------+-------------+-------+-------+-------+----------------------------+----------------------------+---------
      13 |           1 |    13 |     1 |    13 | 2014-10-13 08:24:01.086192 | 2014-10-13 08:24:01.086192 | Teacher
       2 |           2 |     2 |     2 |     2 | 2014-10-13 08:23:59.950349 | 2014-10-16 08:46:02.531245 | Teacher
      12 |           3 |    12 |     3 |    12 | 2014-10-13 08:24:00.984957 | 2014-10-13 08:24:00.984957 | Teacher
       2 |           4 |     2 |     4 |     2 | 2014-10-13 08:23:59.950349 | 2014-10-16 08:46:02.531245 | Teacher
(4 rows)

以前有人遇到过这样的问题吗？我无法理解这里发生了什么.

附：如果你做Resource.all.includes(：教师).map {| r | r.reload.teachers}结果是正确的.然而,它从包含中删除了感觉并提供了N 1问题.

更新：还有一个值得一提的发现.如果我删除STI一切正常.

解决方法

我用pg gem在Rails 4.1.6中重新创建了那些ActiveRecord模型和数据库记录,并看到了正确的行为：

IRB(主)：017：0> Resource.all.includes(：教师).MAP(安培;：教师).MAP(安培;：to_a)资源负载(0.6ms)选择“资源”.* FROM“资源”sql(6.9ms)SELECT“resources_users”.*,“resources_users”.“id”AS t0_r0,“resources_users”.“resource_id”AS t0_r1,“resources_users”.“user_id”AS t0_r2,“users”.“id”AS t1_r0,“users”.“type”AS t1_r1,“users”.“created_at”AS t1_r2,“users”.“updated_at”AS t1_r3 FROM“resources_users”LEFT OUTER JOIN“users”ON“users”.“id”= “resources_users”.“user_id”和“users”.“type”IN(‘Teacher’)WHERE“users”.“type”IN(‘Teacher’)AND“resources_users”.“resource_id”IN(1,4)=> [[#<老师ID：13,输入：“老师”,created_at：“2015-11-05 07:02:59”,updated_at：“2015-11-05 07:02:59”>],[ #<教师ID：2,输入：“Teacher”,created_at：“2015-11-05 07:02:20”,updated_at：“2015-11-05 07:02:32”>],[#&lt ;教师ID：12,created_at：“2015-11-05 07:03:50”,updated_at：“2015-11-05 07:03:50”>],[#<老师id：2,updated_at：“2015-11-05 07:02:32”>]]