I recently ran into a mystical mistake with rails 4 and the HABTM ratio. first of all my gemfile:
source 'https://rubygems.org' gem 'rails', '~> 4.1.6' gem 'pg'
Further. my models:
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
Raw DB data:
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)
Finally the error:
➜ 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) => [ [
As you can see, only the first array of teachers returns to the collection. However, the SQL generated by Rails is correct and returns all the data:
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); user_id | resource_id | t0_r0 | t0_r1 | t1_r0 | t1_r1 | t1_r2 | t1_r3
Has anyone encountered such a problem before? I can not understand what is happening here.
PS If you do Resource.all.includes(:teachers).map { |r| r.reload.teachers } Resource.all.includes(:teachers).map { |r| r.reload.teachers } , the result will be correct. However, it generally eliminates the meaning of include and provides an N + 1 problem.
UPDATE: Another conclusion worth mentioning. If I remove the STI, everything will be fine.