加入嵌套关联（多级）

Question

我有以下模型和关系：

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一个用户有多个报价（他/她是卖家），一个报价有多个购买，一个购买有多个 Accbook

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模型和协会：

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class User < ApplicationRecord\n  has_many :offers, foreign_key: :seller_id\n  has_many :purchases, foreign_key: :buyer_id\nend\n\nclass Offer < ApplicationRecord\n  has_many :purchases\n  belongs_to :seller, class_name: \'User\'\nend\n\nclass Purchase < ApplicationRecord\n  belongs_to :offer\n  belongs_to :buyer, class_name: \'User\'\n  has_one :seller, through: :offer\n  has_many :accbooks,  class_name: \'Admin::Accbook\', foreign_key: \'purchase_id\' \nend\n\nmodule Admin\n  class Accbook < ApplicationRecord\n    belongs_to :purchase\n  end\nend  \n

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我想获取任何给定用户（作为卖家）的所有 Accbook。等效的 SQL 语句如下所示：

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SELECT  "accbooks".* \nFROM "accbooks" \nINNER JOIN "purchases" ON "purchases"."id" = "accbooks"."purchase_id"\nINNER JOIN "offers" ON "offers"."id" = "purchases"."offer_id"\nINNER JOIN "users" ON "users"."id" = "offers"."seller_id"\nWHERE "users"."id" = ?\n

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到目前为止我已经尝试过这个：

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Admin::Accbook.joins( {purchase: :offer} )\n

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这给了我这个 SQL 结果：

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SELECT  "accbooks".*\nFROM "accbooks"\nINNER JOIN "purchases" ON "purchases"."id" = "accbooks"."purchase_id"\nINNER JOIN "offers" ON "offers"."id" = "purchases"."offer_id"\n

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现在我不知道如何将联接添加到用户模型，然后如何添加Where 条件。

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感谢您的任何见解。

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Answer 1

您可以将joins关系放在一起并where在连接关系上应用条款：

Admin::Accbook
  .joins(purchase: :offer)
  .where(offers: { seller_id: 123 })

需要知道的是，where使用数据库表的名称。joins（和includes、eager_load等）使用关系名称。这就是为什么我们有：

Admin::Accbook
  .joins(purchase: :offer)
  #                 ^^^^^ relation name
  .where(offers: { seller_id: 123 })
  #      ^^^^^^ table name