Rails mysql: 如何查询具有深层嵌套关系（has_many 和belongs_to）的表？

Question

我有以下型号：

class User < ActiveRecord::Base
  has_many :keys
end

class Key < ActiveRecord::Base
  belongs_to :room
end

class Room < ActiveRecord::Base
  belongs_to :building
end

class Building < ActiveRecord::Base
  #Has column "name"
end

我想获取所有拥有属于名称为 "HQ"

的建筑物的钥匙的用户

基本上是这样的（伪查询）：

Users = users.where('keys.room.building.name=?', name)

这是我得到的最远的：

users = User.joins(:keys).where('keys.room.building.name=?', name)

但它给出了以下错误：

ActionView::Template::Error (Mysql2::Error: You have an error in your SQL syntax; 
check the manual that corresponds to your MySQL server version for the right syntax to use near '.name='HQ')' at line 1: 
SELECT `users`.* FROM `users` INNER JOIN `keys` ON `keys`.`user_id` = `users`.`id` WHERE (keys.room.building.name='HQ')):

Answer 1

试一试

User.joins(keys: [room: :building]).where("buildings.name" => name)

Answer 2

试试这个：-

User.joins(:keys => {:room => {:building}}).where("buildings.name" => name)

假设您还想预加载避免 1+N 次查询：

User.includes(:keys => {:room => {:building}}).where("buildings.name" => name)

希望这对你有用！！

Rails mysql: 如何查询具有深层嵌套关系（has_many 和belongs_to）的表？

Rails mysql: How to query tables with deeply nested relations(has_many and belongs_to)?

mysql

ruby-on-rails

has-many

belongs-to