如何创建自引用关联表边栏迁移

Question

假设我有一个表products并希望为每个产品维护similar_products。

Answer 1

这是自引用表的迁移。

create_table :similar_products, id: false do |t|
      t.references :product, foreign_key: true, null: false
      t.references :similar_product, foreign_key: { to_table: :similar_products }
    end

Answer 2

class SimilarProductRelation < ApplicationRecord
  belongs_to :product
  belongs_to :similar_product, class_name: "Product"
end
class Product < ApplicationRecord
  # self being the "origin"
  has_many :similar_products_relations, source: :product_id, class_name: "SimilarProductRelation"
  has_many :similar_products, class_name: "Product", through: :similar_products_relations
  # self being the "destination"
  has_many :similar_products_relations_as, source: :similar_product_id, class_name: "SimilarProductRelation"
  has_many :similar_products_as, class_name: "Product", through: :similar_products_relations
end
# migration
create_table :similar_product_relations do |t|
  t.references :product, foreign_key: true, null: false, index: true
  t.references :similar_product, foreign_key: { to_table: :products }, null: false, index: true 
end

索引是否为真取决于要进行查询的方向，并且如果您只打算使用一个方向，则只能在关联中保留一个方向，即Product类中。

Answer 3

您可以尝试以下方法：

class Product < ActiveRecord::Base
   belongs_to :product, :class_name => 'Product'
   has_many :similar_products, :class_name => 'Product', :foreign_key => 'parent_id'
end

迁移可以添加为：

add_column :products, :parent_id, :integer, null: true, index: true
add_foreign_key :products, :products, column: :parent_id