将 SQL 查询从关联切换到实例方法

Question

我现在的User.rb模特

class User < ApplicationRecord
  has_many :children,
           -> (user) { unscope(:where).where("father_id = :id OR mother_id = :id", id: user.id) },
           class_name: "User"

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

  belongs_to :mother, class_name: "User", optional: true
  belongs_to :father, class_name: "User", optional: true
end

我目前的数据（空的为nil）：

所有查询现在都有效：

但是对于 .grandchildren 查询，您可以看到在控制台中创建了三个（两个重复查询）查询。有没有办法只生成一个查询？

我正在尝试实例方法，因为我可以输入原始 SQL，但似乎无法理解它。一个例子：

  def children
    sql = ("SELECT users.* FROM users WHERE (father_id = id OR mother_id = id)")
    p ActiveRecord::Base.connection.execute(sql)
  end

最终目标：

执行 .grandchildren

Answer 1

你可以替换

-> (user) { unscope(:where).where("father_id IN (:ids) OR mother_id IN (:ids)", ids: user.children.ids) },

有

-> (user) do
  scope = unscope(:where)
  children_ids = user.children.select(:id)

  scope
    .where(father_id: children_ids)
    .or(scope.where(mother_id: children_ids))
end

Answer 2

解决了

  has_many :children,
  -> (user) { unscope(:where).where("father_id = :id OR mother_id = :id", id: user.id) },
   class_name: "User"

  belongs_to :mother, class_name: "User", optional: true
  belongs_to :father, class_name: "User", optional: true

  def grandchildren
    user_id = self.id
    User.where(
      "father_id IN (:ids) OR mother_id IN (:ids)",
      ids: User.where("father_id = :id OR mother_id = :id", id: user_id).pluck(:id)
    )
  end

将 SQL 查询从关联切换到实例方法

Switching SQL queries from association into instance methods

ruby

sql

ruby-on-rails

associations

self-join