Rails 4 has_and_belongs_to_many non funziona correttamente con l'istruzione include

Recentemente mi sono imbattuto in bug mistico con le relazioni rail 4 e HABTM. prima di tutto la mia Gemfile:Rails 4 has_and_belongs_to_many non funziona correttamente con l'istruzione include

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

Avanti. i miei modelli:

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 di dati:

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)

Infine il 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">], 
[], 
[], 
[]]

Come si vede solo prima schiera di insegnanti restituiti in collezione. Tuttavia SQL generato da Rails è corretto e restituisce tutti i dati:

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 
---------+-------------+-------+-------+-------+----------------------------+----------------------------+--------- 
     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)

Ha fatto qualcuno ha affrontato tale problema prima? Non riesco a capire cosa sta succedendo qui.

P.S. Se lo fai, Resource.all.includes(:teachers).map { |r| r.reload.teachers } il risultato è corretto. Tuttavia rimuove completamente il senso da include e fornisce il problema N + 1.

AGGIORNAMENTO: un'altra scoperta che vale la pena menzionare. Se rimuovo STI, tutto funziona correttamente.

fonte

2014-10-22 Pavel S

Voglio solo ricordare qui che 'has_and_belongs_to_many' è una sorta di modo vecchia scuola per le relazioni molti-a-molti. Un'alternativa migliore è "has_many: through'. [Fonte] (http://aihuiong.com/post/829841945/rails-hasandbelongstomany-vs-hasmany-through) – zhurora

Voglio solo dire che non c'è niente "vecchia scuola" su "has_and_belongs_to_many', dovresti usare il tipo di associazione che è più adatto per il tuo compito. Per un sacco di cose, HABTM è perfettamente a posto. – sevenseacat

Ho ricreato quei ActiveRecord modelli e record del database in Rails 4.1.6 con pg gemma e ha visto il comportamento corretto:

irb(main):017:0> Resource.all.includes(:teachers).map(&:teachers).map(&:to_a) Resource Load (0.6ms) SELECT "resources".* FROM "resources" 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" AND "users"."type" IN ('Teacher') WHERE "users"."type" IN ('Teacher') AND "resources_users"."resource_id" IN (1, 2, 3, 4) => [[#<Teacher id: 13, type: "Teacher", created_at: "2015-11-05 07:02:59", updated_at: "2015-11-05 07:02:59">], [#<Teacher id: 2, type: "Teacher", created_at: "2015-11-05 07:02:20", updated_at: "2015-11-05 07:02:32">], [#<Teacher id: 12, type: "Teacher", created_at: "2015-11-05 07:03:50", updated_at: "2015-11-05 07:03:50">], [#<Teacher id: 2, type: "Teacher", created_at: "2015-11-05 07:02:20", updated_at: "2015-11-05 07:02:32">]]

fonte

2015-11-05 07:06:44

stesso bug qui con Rails 4.1.6 e pg, ma posso ottenere il comportamento corretto non rimuovendo il campo resources_usersid nella migrazione:

def change 
    #create_table :resources_users, id: false do |t| 
    create_table :resources_users do |t| 
    t.integer :resource_id 
    t.integer :user_id 
    end 
end

anche eager_load opere in b casi OTH (con o senza id sul tavolo join) e avere i benefici di una singola query SQL:

Resource.eager_load(:teachers).map(&:teachers).map(&:to_a)

uscita:

irb(main):002:0> Resource.eager_load(:teachers).map(&:teachers).map(&:to_a) 
SQL (1.0ms) SELECT "resources"."id" AS t0_r0, "resources"."created_at" 
AS t0_r1, "resources"."updated_at" 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" LEFT OUTER JOIN 
"resources_users" ON "resources_users"."resource_id" = "resources"."id" 
LEFT OUTER JOIN "users" ON "users"."id" = "resources_users"."user_id" 
AND "users"."type" IN ('Teacher') 
=> [[#<Teacher id: 1, type: "Teacher", created_at: "2015-11-05 
15:02:33", updated_at: "2015-11-05 15:02:33">], [#<Teacher id: 2, type: 
"Teacher", created_at: "2015-11-05 15:02:33", updated_at: "2015-11-05 
15:02:33">], [#<Teacher id: 2, type: "Teacher", created_at: "2015-11-05 
15:02:33", updated_at: "2015-11-05 15:02:33">], [#<Teacher id: 3, type: 
"Teacher", created_at: "2015-11-05 15:02:33", updated_at: "2015-11-05 
15:02:33">]]

fonte

2015-11-05 15:23:46 ehoffmann

Rails 4 has_and_belongs_to_many non funziona correttamente con l'istruzione include

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