在实例相关范围的情况下解决 N + 1

Question

所以，我有麻烦

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Preloading instance dependent scopes are not supported.\n

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我有三个型号

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Preloading instance dependent scopes are not supported.\n

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class P < ApplicationRecord\n  has_many :as\n  has_many :cs\nend\n

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class C < ApplicationRecord\n  belongs_to :p\nend\n

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我有三个 fast_jsonapi 序列化器

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

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class PSerializer\n  include FastJsonapi::ObjectSerializer\n  has_many :as\nend\n

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class CSerializer\n  include FastJsonapi::ObjectSerializer\n  belongs_to :p\nend\n

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还有这个种子文件

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class ASerializer\n  include FastJsonapi::ObjectSerializer\n  belongs_to :p\n  has_one :c\nend\n

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我想用他的 A 和 A\xe2\x80\x99s C\xe2\x80\x99s\n渲染 P 但当我尝试这样做时

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

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我有

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  P Load (0.1ms)  SELECT  "ps".* FROM "ps" ORDER BY "ps"."id" ASC LIMIT ?  [["LIMIT", 1]]\n   (0.1ms)  SELECT "as"."id" FROM "as" WHERE "as"."p_id" = ?  [["p_id", 1]]\n  A Load (0.1ms)  SELECT "as".* FROM "as" WHERE "as"."p_id" = ?  [["p_id", 1]]\n  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]]\n  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]]\n  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]]\n  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]]\n

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所以，看起来像 N + 1。但我知道我可以使用 include 来解决它。

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

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哎呀：

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

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我可以尝试使用 left_joins

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

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实际上是一样的。\n我该如何解决这个 N + 1 问题？

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我用这些模型创建了 Rails 存储库，因此您可以自行尝试。\n https://github.com/X1ting/reproduct_preload_bug \nRails 5.2.3\nRuby 2.5.1

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Answer 1

非常感谢@igor-khodyrev

他建议我使用复合键，效果很好！所以，解决方案：

将 gem 添加到 Gemfile

gem 'composite_primary_keys', '=11'

并将 A 模型中的关联更改为此

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

N+1 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 添加到了我的存储库中。 https://github.com/X1ting/reproduct_preload_bug/pull/1