Question

我在Rails应用程序中有3个嵌套模型：

class User < ApplicationRecord
  has_many :products, dependent: :destroy
end

class Product < ApplicationRecord
  belongs_to :user
  has_one :insurance_policy
end

class InsurancePolicy < ApplicationRecord
  belongs_to :product, -> { includes :user }
end

我试图避免这样做：

InsurancePolicy.last.product.user

使用includes_to方法的include附加内容，我得到以下错误消息：

[10] pry(main)> InsurancePolicy.last.user
  InsurancePolicy Load (0.4ms)  SELECT  "insurance_policies".* FROM "insurance_policies" ORDER BY "insurance_policies"."id" DESC LIMIT $1  [["LIMIT", 1]]
NoMethodError: undefined method `user' for #<InsurancePolicy:0x00007fc50a2d5a10>
from /Users/albert/.rbenv/versions/2.4.4/lib/ruby/gems/2.4.0/gems/activemodel-5.2.0/lib/active_model/attribute_methods.rb:430:in `method_missing'

为什么缺少该方法？我需要在我的insurance_policies表中添加一列user_id吗？

我正在遵循AR的官方文档。

class LineItem < ApplicationRecord
  belongs_to :book, -> { includes :author }
end

class Book < ApplicationRecord
  belongs_to :author
  has_many :line_items
end

class Author < ApplicationRecord
  has_many :books
end

这是我所缺少的吗？我不太了解：

If you use the select method on a belongs_to association, you should also set the :foreign_key option to guarantee the correct results.

Answer 1

调用InsurancePolicy.last.user是错误的，因为InsurancePolicy模型与User模型没有关联。

关联belongs_to :product, -> { includes :user }也是不正确的，因为模型Product与User模型没有关联。为了使includes正常工作，您需要将其添加到Product：

belongs_to :user

之后InsurancePolicy.last.product.user应该可以工作。

更新：

没有belongs_to through关联，您可以用来直接从User访问InsurancePolicy模型。要使InsurancePolicy.last.user工作，只需将该关联定义为InsurancePolicy的方法：

def user
  product.user
end

所属的Rails包含未识别的二阶关联

1 个答案: