通过 has_many 进行多个数据库连接

Question

如何通过使用多个数据库连接来创建 has_many ？

我有一个名为“master”的数据库，其中保存位置信息。这是从单独的应用程序更新的。用户可以访问许多位置，但所有其他模型都位于另一个名为“budget”的数据库中。以下是模型的设置方式。

# place.rb
class Place < ActiveRecord::Base
  belongs_to :user
  belongs_to :location
end

# user.rb
class User < ActiveRecord::Base
  has_many :locations, :through => :places
  has_many :places
end

# location.rb
class Location < ActiveRecord::Base
  establish_connection "master"
  has_many :places
  has_many :users, :through => :places
end

当我通过 irb 运行命令时，我得到以下信息

> Location.first.places.create(:user_id => 1)
> #<Place id: 1, user_id: 1, location_id: 1, created_at: "2011-11-28 20:58:43",  updated_at: "2011-11-28 20:58:43">

> Location.first.places
> [#<Place id: 1, user_id: 1, location_id: 1, created_at: "2011-11-28 20:58:43", updated_at: "2011-11-28 20:58:43">]

> Location.first.users
> [#<User id: 1, username: "toby", role: "guest", created_at: "2011-11-28 17:45:40", updated_at: "2011-11-28 17:45:40">

> User.first.locations
> Mysql2::Error: Table 'master.places' doesn't exist: SELECT `locations`.* FROM `locations` INNER JOIN `places` ON `locations`.`id` = `places`.`location_id` WHERE `places`.`user_id` = 1 ActiveRecord::StatementInvalid: Mysql2::Error: Table 'master.places' doesn't exist: SELECT `locations`.* FROM `locations` INNER JOIN `places` ON `locations`.`id` = `places`.`location_id` WHERE `places`.`user_id` = 1

我尝试将当前的 Rails env 添加到 Place 来尝试覆盖 place 的默认数据库，如下所示： # 地点.rb 班级地点< ActiveRecord::基础 建立_连接Rails.env 属于：用户 属于：位置 这

#database.yml

master:
  adapter: mysql2
  encoding: utf8
  reconnect: false
  database: master
  pool: 5
  username: root
  password:
  socket: /var/run/mysqld/mysqld.sock
development:
  adapter: mysql2
  encoding: utf8
  reconnect: false
  database: budget_development
  pool: 5
  username: root
  password:
  socket: /var/run/mysqld/mysqld.sock

没有帮助。有什么想法吗？

Answer 1

一位朋友帮我回答了这个问题，我想这可能对其他人有用。

class Location < ActiveRecord::Base
  #establish_connection "master"
  def self.table_name() "master.locations" end
  has_many :places
  has_many :users, :through => :places
end

Answer 2

答案对我有用，但我在关系表中使用这个版本：

self.table_name = "master.locations"

Answer 3

几年后阅读本文的任何人都请注意，Rails 7 已为 has_one 和 has_many 引入了显式 disable_joins: true 选项。

参考： https://edgeguides.rubyonrails.org/ active_record_multiple_databases.html#handling-associations-with-joins-across-databases