两个belongs_to关联的相同模型

Question

我有一个模型PointOfContact has_many Systems。从Systems方面，我想将PointOfContact确定为technical_manager或project_manager（或两者）。虽然仍然只在数据库中保持PointOfContact 1次。

我的尝试如下：

class System < ActiveRecord::Base
  belongs_to :project_manager, :class_name => 'PointOfContact'
  belongs_to :technical_manager, :class_name => 'PointOfContact'
end

class PointOfContact < ActiveRecord::Base
  has_many :systems
end

当我运行我的规范（示例如下）时，我可以正确创建System联系人关联点。但是，PointOfContact并不知道它与System的关联。这是为什么？

@sys = System.create
@tm = PointOfContact.create
@pm = PointOfContact.create

@sys.project_manager = @pm
@sys.technical_manager = @tm

@pm.systems.should have(1).items #> expected 1 items, got 0

Answer 1

感谢jamesw在RailsForum.com：Same Model for Two belongs_to Associations找到了一个解决方案。

class System < ActiveRecord::Base
  belongs_to :project_manager, :class_name => 'PointOfContact', :foreign_key => 'project_manager_id'
  belongs_to :technical_manager, :class_name => 'PointOfContact', :foreign_key => 'technical_manager_id'
end

class PointOfContact < ActiveRecord::Base
  has_many :project_managed_systems, :class_name => 'System', :foreign_key => 'project_manager_id'
  has_many :technical_managed_systems, :class_name => 'System', :foreign_key => 'technical_manager_id'
end

Answer 2

从Rails文档：

• https://guides.rubyonrails.org/association_basics.html#self-joins
• https://guides.rubyonrails.org/association_basics.html#options-for-has-one

注释示例：

# Employee class with two Employee associations
class Employee < ApplicationRecord

  # Employees I manage
  has_many :subordinates, class_name: "Employee",
                          foreign_key: "manager_id"

  # Employee that manages me
  # NOTE: with :manager reference name, foreign_key defaults to "manager_id",
  # hence it is not needed as above. Favor "convention over configuration".
  belongs_to :manager, class_name: "Employee"
end