背景

• 项目使用了多个数据库
• user 表在 system 库
• friends_relations 表在 thalassa 库
• thalassa 是默认库

目的

实现查找某个用户的所有好友

实现

user model 的代码

class System::User < System::BaseDb
  self.abstract_class = true
  establish_connection :system
  self.table_name = "system.users"

  has_many :friend_relationships
  has_many :friends, through: :friend_relationships, source: :user
end

friend_relationships model 的代码

class FriendRelationship < ActiveRecord::Base

  belongs_to :user, :class_name => "System::User"
  belongs_to :friend, :class_name => "System::User"
end

这样配置是会报错的

Mysql2::Error: Table 'system.friend_relationships' doesn't exist

在 FriendRelationship 这个 model 中加上一行代码能解决这个问题

class FriendRelationship < ActiveRecord::Base
  self.table_name = "thalassa.friend_relationships"

  belongs_to :user, :class_name => "System::User"
  belongs_to :friend, :class_name => "System::User"
end