rails ruby 中 child 的 child 协会

Question

用户中的数据示例 table

rails 控制台中的预期结果，grandfather.grandchildren 和 grandmother.grandchildren 应该 return 同一组 objects:

grandfather = User.first
grandfather.grandchildren
=> #<ActiveRecord::Associations::CollectionProxy [#<User id: 5, name: "father's son", father_id: 3, mother_id: nil>, #<User id: 6, name: "uncle's son", father_id: 4, mother_id: nil>]>
grandmother = User.find(2)
grandmother.grandchildren
=> #<ActiveRecord::Associations::CollectionProxy [#<User id: 5, name: "father's son", father_id: 3, mother_id: nil>, #<User id: 6, name: "uncle's son", father_id: 4, mother_id: nil>]>

这是我现在在 User.rb 模型中的协会。

 has_many :children, ->(user) { unscope(:where).where("father_id = :id OR mother_id = :id", id: user.id) }, class_name: "User"
 has_many :grandchildren, through: :children, source: :children
 belongs_to :mother, class_name: "User", optional: true
 belongs_to :father, class_name: "User", optional: true

现在 rails 控制台中的输出：

irb(main):001:0> grandfather = User.first
   (0.3ms)  SELECT sqlite_version(*)
  User Load (0.2ms)  SELECT "users".* FROM "users" ORDER BY "users"."id" ASC LIMIT ?  [["LIMIT", 1]]
=> #<User id: 1, name: "grandfather", mother_id: nil, father_id: nil>

irb(main):002:0> grandfather.grandchildren
  User Load (0.3ms)  SELECT "users".* FROM "users" INNER JOIN "users" "children_grandchildren" ON "users"."user_id" = "children_grandchildren"."id" WHERE (father_id = 1 OR mother_id = 1) /* loading for inspect */ LIMIT ?  [["LIMIT", 11]]
Traceback (most recent call last):
ActiveRecord::StatementInvalid (SQLite3::SQLException: ambiguous column name: father_id)

Answer 1

你不能通过 children 从祖父母那里得到祖父母的祖父母 children 因为这意味着他们的 father/mother id 等于祖父母，它不穿越盛大childrenparents:

SELECT "users".*
FROM "users"
INNER JOIN "users" "children_grandchildren"
ON "users"."user_id" = "children_grandchildren"."id"
WHERE (father_id = 1 OR mother_id = 1) -- this is the grandparent id, when it should be the child parent's id

你可以添加一个callable到grandchildren关系，类似于children的关系，但是这次提取祖父母[=21] =] ids，并使用 IN 子句过滤那些匹配这些 ids 的用户行，他们的 father/mother ids:

has_many :grandchildren,
  ->(user) { unscope(:where).where('father_id IN (:ids) OR mother_id IN (:ids)', ids: user.children.ids) },
  class_name: "User"

rails ruby 中 child 的 child 协会

Association for the child of the child in ruby on rails

ruby

sql

ruby-on-rails

associations

self-join