实例依赖作用域解析N+1

Question

所以，我遇到了麻烦

Preloading instance dependent scopes are not supported.

我有三个型号

class P < ApplicationRecord
  has_many :as
  has_many :cs
end

class C < ApplicationRecord
  belongs_to :p
end

class A < ApplicationRecord
  belongs_to :p
  has_one :c, -> (a) { where(feature: a.feature) }, through: :p, source: :cs
end

我有三个fast_jsonapi序列化程序

class PSerializer
  include FastJsonapi::ObjectSerializer
  has_many :as
end

class CSerializer
  include FastJsonapi::ObjectSerializer
  belongs_to :p
end

class ASerializer
  include FastJsonapi::ObjectSerializer
  belongs_to :p
  has_one :c
end

这是一个种子文件

p_model = P.create(title: 'PTitle')
4.times do |i|
  A.create(title: "aTitle-#{i}", feature: "feature-#{i}", p: p_model)
  C.create(title: "cTitle-#{i}", feature: "feature-#{i}", p: p_model)
end

我想用他的A和A的C来表示P，但是当我尝试这样做时

PSerializer.new(P.first, { include: [:as, :'as.c'] }).serialized_json

我得到了

  P Load (0.1ms)  SELECT  "ps".* FROM "ps" ORDER BY "ps"."id" ASC LIMIT ?  [["LIMIT", 1]]
   (0.1ms)  SELECT "as"."id" FROM "as" WHERE "as"."p_id" = ?  [["p_id", 1]]
  A Load (0.1ms)  SELECT "as".* FROM "as" WHERE "as"."p_id" = ?  [["p_id", 1]]
  C Load (0.2ms)  SELECT  "cs".* FROM "cs" INNER JOIN "ps" ON "cs"."p_id" = "ps"."id" WHERE "ps"."id" = ? AND "cs"."feature" = ? LIMIT ?  [["id", 1], ["feature", "feature-0"], ["LIMIT", 1]]
  C Load (0.1ms)  SELECT  "cs".* FROM "cs" INNER JOIN "ps" ON "cs"."p_id" = "ps"."id" WHERE "ps"."id" = ? AND "cs"."feature" = ? LIMIT ?  [["id", 1], ["feature", "feature-1"], ["LIMIT", 1]]
  C Load (0.1ms)  SELECT  "cs".* FROM "cs" INNER JOIN "ps" ON "cs"."p_id" = "ps"."id" WHERE "ps"."id" = ? AND "cs"."feature" = ? LIMIT ?  [["id", 1], ["feature", "feature-2"], ["LIMIT", 1]]
  C Load (0.1ms)  SELECT  "cs".* FROM "cs" INNER JOIN "ps" ON "cs"."p_id" = "ps"."id" WHERE "ps"."id" = ? AND "cs"."feature" = ? LIMIT ?  [["id", 1], ["feature", "feature-3"], ["LIMIT", 1]]

所以，看起来像N+ 1。但是我知道我可以用includes来解决它。

PSerializer.new(P.includes({ as: :c }).first, { include: [:as, :'as.c'] }).serialized_json

糟了：

irb(main):010:0> PSerializer.new(P.includes({ as: :c }).first, { include: [:as, :'as.c'] }).serialized_json
  P Load (0.1ms)  SELECT  "ps".* FROM "ps" ORDER BY "ps"."id" ASC LIMIT ?  [["LIMIT", 1]]
  A Load (0.1ms)  SELECT "as".* FROM "as" WHERE "as"."p_id" = ?  [["p_id", 1]]
Traceback (most recent call last):
        1: from (irb):10
ArgumentError (The association scope 'c' is instance dependent (the scope block takes an argument). Preloading instance dependent scopes is not supported.)

我可以试试left_joins

irb(main):011:0> PSerializer.new(P.left_joins({ as: :c }).first, { include: [:as, :'as.c'] }).serialized_json
Traceback (most recent call last):
        1: from (irb):11
ArgumentError (The association scope 'c' is instance dependent (the scope block takes an argument). Preloading instance dependent scopes is not supported.)

实际上是一样的。如何解决此N+1问题？

我使用这些模型创建了rails代码库，因此您可以自己尝试。Rails 5.2.3 https://github.com/X1ting/reproduce_preload_bug 2.5.1

Answer 1

非常感谢@igor-khodyrev

他建议我使用组合键，它起作用了！所以，解决方案：

将gem添加到Gemfile

gem 'composite_primary_keys', '=11'

并将模型中的关联更改为

  has_one :c, foreign_key: [:p_id, :feature], primary_key: [:p_id, :feature]

N+1已解决：

irb(main):005:0> PSerializer.new(P.includes({ as: :c }).first, { include: [:as, :'as.c'] }).serialized_json
  P Load (0.2ms)  SELECT  "ps".* FROM "ps" ORDER BY "ps"."id" ASC LIMIT ?  [["LIMIT", 1]]
  A Load (0.1ms)  SELECT "as".* FROM "as" WHERE "as"."p_id" = ?  [["p_id", 1]]
  C Load (0.1ms)  SELECT "cs".* FROM "cs" WHERE ("cs"."p_id" = 1 AND "cs"."feature" = 'feature-0' OR "cs"."p_id" = 1 AND "cs"."feature" = 'feature-1' OR "cs"."p_id" = 1 AND "cs"."feature" = 'feature-2' OR "cs"."p_id" = 1 AND "cs"."feature" = 'feature-3' OR "cs"."p_id" = 1 AND "cs"."feature" = 'feature-kek')
=> "{\"data\":{\"id\":\"1\",\"type\":\"p\",\"relationships\":{\"as\":{\"data\":[{\"id\":\"1\",\"type\":\"a\"},{\"id\":\"2\",\"type\":\"a\"},{\"id\":\"3\",\"type\":\"a\"},{\"id\":\"4\",\"type\":\"a\"},{\"id\":\"5\",\"type\":\"a\"}]}}},\"included\":[{\"id\":\"1\",\"type\":\"a\",\"relationships\":{\"p\":{\"data\":{\"id\":\"1\",\"type\":\"p\"}},\"c\":{\"data\":{\"id\":\"1\",\"type\":\"c\"}}}},{\"id\":\"2\",\"type\":\"a\",\"relationships\":{\"p\":{\"data\":{\"id\":\"1\",\"type\":\"p\"}},\"c\":{\"data\":{\"id\":\"2\",\"type\":\"c\"}}}},{\"id\":\"3\",\"type\":\"a\",\"relationships\":{\"p\":{\"data\":{\"id\":\"1\",\"type\":\"p\"}},\"c\":{\"data\":{\"id\":\"3\",\"type\":\"c\"}}}},{\"id\":\"4\",\"type\":\"a\",\"relationships\":{\"p\":{\"data\":{\"id\":\"1\",\"type\":\"p\"}},\"c\":{\"data\":{\"id\":\"4\",\"type\":\"c\"}}}},{\"id\":\"5\",\"type\":\"a\",\"relationships\":{\"p\":{\"data\":{\"id\":\"1\",\"type\":\"p\"}},\"c\":{\"data\":null}}},{\"id\":\"1\",\"type\":\"c\",\"relationships\":{\"p\":{\"data\":{\"id\":\"1\",\"type\":\"p\"}}}},{\"id\":\"2\",\"type\":\"c\",\"relationships\":{\"p\":{\"data\":{\"id\":\"1\",\"type\":\"p\"}}}},{\"id\":\"3\",\"type\":\"c\",\"relationships\":{\"p\":{\"data\":{\"id\":\"1\",\"type\":\"p\"}}}},{\"id\":\"4\",\"type\":\"c\",\"relationships\":{\"p\":{\"data\":{\"id\":\"1\",\"type\":\"p\"}}}}]}"

我还将解决方案PR添加到我的存储库中。https://github.com/X1ting/reproduce_preload_bug/pull/1