ruby-on-rails - 具有多个外键的 Rails 预加载关联

Question

假设我有以下两个模型，分别由以下两个连接模型连接:

class Game
  has_many :game_plays
  has_many :game_views
end

class Person
  has_many :game_plays
  has_many :game_views
end

# Games that a Person has played
class GamePlay
  belongs_to :game
  belongs_to :person
end

# Games that a Person has viewed
class GameView
  belongs_to :game
  belongs_to :person
end

给定一个特定的 GamePlay，我想为同一个 Person-Game 组合获取 GameView，例如:

game_play = GamePlay.first
game_view = GameView.find_by(game_id: game_play.game_id, person_id: game_play.person_id)

我还需要预先加载该关联。

---

我很想在 GamePlay 和 GameView 之间建立关联，但目前为止我尝试过的都没有效果。

尝试 1

class GamePlay
  belongs_to :game
  belongs_to :person

  has_one :game_view, -> (gp) { where(game_id: gp.game_id) }, foreign_key: :person_id, primary_key: :person_id
end

这行得通，但我不能包含这个:

GamePlay.includes(:game_view).first
# => ArgumentError: The association scope 'game_view' is instance dependent (the scope block takes an argument). Preloading instance dependent scopes is not supported.

尝试 2

class GamePlay
  belongs_to :game
  belongs_to :person

  def game_view
    GameView.find_by(game_id: game_id, person_id: person_id)
  end
end

这显然有效，但我不能包括它，因为它没有定义为关联。

有什么想法吗？谢谢!

Rails 5.0.0
postgres 9.6.2

Answer 1

怎么样:

class GamePlay < ApplicationRecord
  belongs_to :game
  belongs_to :person
  has_one :game_view, through: :person, source: :game_views
end

irb(main):002:0> GamePlay.includes(:game_view).find(2)
  GamePlay Load (0.2ms)  SELECT  "game_plays".* FROM "game_plays" WHERE "game_plays"."id" = ? LIMIT ?  [["id", 2], ["LIMIT", 1]]
  Person Load (0.2ms)  SELECT "people".* FROM "people" WHERE "people"."id" = 1
  GameView Load (0.2ms)  SELECT "game_views".* FROM "game_views" WHERE "game_views"."person_id" = 1
=> #<GamePlay id: 2, game_id: 1, person_id: 1>

irb(main):008:0> GamePlay.find(2).game_view
  GamePlay Load (0.1ms)  SELECT  "game_plays".* FROM "game_plays" WHERE "game_plays"."id" = ? LIMIT ?  [["id", 2], ["LIMIT", 1]]
  GameView Load (0.2ms)  SELECT  "game_views".* FROM "game_views" INNER JOIN "people" ON "game_views"."person_id" = "people"."id" WHERE "people"."id" = ? LIMIT ?  [["id", 1], ["LIMIT", 1]]
=> #<GameView id: 2, game_id: 1, person_id: 1>