两个 belongs_to 关联的相同模型答案

【问题标题】：Same Model for Two belongs_to Associations两个 belongs_to 关联的相同模型
【发布时间】：2011-03-14 04:34:37
【问题描述】：

我有一个模型PointOfContact，其中has_manySystems。从Systems 方面，我想将PointOfContact 标识为technical_manager 或project_manager（或两者）。虽然仍然只在数据库中保留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

当我运行我的规范时（示例如下），我可以正确创建System 联系点关联。但是，PointOfContact 不知道它与 System.这是为什么呢？

@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

【问题讨论】：

标签： ruby-on-rails-3 associations model-associations

【解决方案1】：

感谢 RailsForum.com 上的 jamesw：Same Model for Two belongs_to Associations 找到了解决方案。

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

【讨论】：

更多详情：通过link上的关系

【解决方案2】：

来自 Rails 文档：

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

【讨论】：