active admin many to many show index PG::UndefinedColumn: ERROR: column cases.product_id does not exist

Question

在我的 Case 模型中

  has_many :case_products, dependent: :destroy
  has_many :products, through: :case_products

在我的 Product 模型中

class Product < ActiveRecord::Base
  has_many :cases
end

在CaseProduct

class CaseProduct < ActiveRecord::Base
  belongs_to :case
  belongs_to :product
end

如何显示每种产品有多少箱子？

在active admin product.rb

ActiveAdmin.register Product do
  permit_params :id, :name ,case_ids: []
  index do
    column :id
    column :name
    column "case" do |m|
      m.cases.count
    end

    actions

  end
  
  show do
      attributes_table do
        row :id
        row :name
        row :case
        
      end 
  end

end

我遇到了这个错误

PG::UndefinedColumn: ERROR:  column cases.product_id does not exist
LINE 1: SELECT COUNT(*) FROM "cases" WHERE "cases"."product_id" = 
                                           ^
: SELECT COUNT(*) FROM "cases" WHERE "cases"."product_id" = 

Answer 1

您必须像案例模型一样在产品中设置关联：

class Product < ActiveRecord::Base
  has_many :case_products, dependent: :destroy
  has_many :cases, through: :case_products
end

如果您只使用 has_many :cases，Rails 假设案例模型有一个 product_id 列。