has_many :通过与反向添加两次的关联

Question

我创建了一个示例应用程序来启发我的问题。

基本上，我与 STI 类有多对多关联：

class Basket < ActiveRecord::Base
  has_many :basket_fruits, inverse_of: :basket
  has_many :fruits, through: :basket_fruits
  has_many :apples, through: :basket_fruits, source: :fruit, class_name: 'Apple'
  has_many :oranges, through: :basket_fruits, source: :fruit, class_name: 'Orange'
  has_many :bananas, through: :basket_fruits, source: :fruit, class_name: 'Banana'
end
class BasketFruit < ActiveRecord::Base
  belongs_to :basket, inverse_of: :basket_fruits
  belongs_to :fruit, inverse_of: :basket_fruits
  validates :basket, :fruit, presence: true
end
class Fruit < ActiveRecord::Base
  has_many :basket_fruits, inverse_of: :fruit
  has_many :baskets, through: :basket_fruits
  validates :type, presence: true, inclusion: ['Apple', 'Banana', 'Orange']
  validates :baskets, presence: true
end
class Apple < Fruit; end
class Banana < Fruit; end
class Orange < Fruit; end

图式：

Basket(id: integer, created_at: datetime, updated_at: date time)
BasketFruit(id: integer, fruit_id: integer, basket_id: integer, created_at: datetime, updated_at: date time)
Fruit(id: integer, type: string, created_at: datetime, updated_at: datetime)

当使用ActiveAdmin创建新的Banana财务会计软件时，它使用的代码等效于：

Basket.create
banana = Basket.first.bananas.build(basket_ids: [Basket.first.id])

出现的问题是此代码创建了两个关联，即使不保存 Banana 浏览器也可以观察到：

banana.basket_fruits.size
=> 2

为什么会发生这种情况，以及如何解决？

更新

刚刚发现这个。也许这就是为什么AR试图两次添加关系，而不是像我预期的那样"覆盖"：

banana = Basket.first.bananas.build
=> #<Banana id: nil, type: "Banana", created_at: nil, updated_at: nil>
banana.baskets
=> #<ActiveRecord::Associations::CollectionProxy []>

在这种情况下，需要在调用#build后预先填充关联

Answer 1

为什么要分配两次篮子？

 Basket.first.bananas.build(basket_ids: [Basket.first.id])

我会这样写：

 Basket.first.bananas.build