如何通过尚未保存的父关联访问 ActiveRecord 祖父母关联？

我有一种情况，我想在保存父对象之前访问关联的祖父母。我可以想到几种技巧，但我正在寻找一种干净的方法来完成此任务。以下面的代码来说明我的问题：

class Company < ActiveRecord::Base
  has_many :departments
  has_many :custom_fields
  has_many :employees, :through => :departments
end
class Department < ActiveRecord::Base
  belongs_to :company
  has_many :employees
end
class Employee < ActiveRecord::Base
  belongs_to :department
  delegate :company, :to => :department
end

company = Company.find(1)           # => <Company id: 1>
dept = company.departments.build    # => <Department id: nil, company_id: 1>
empl = dept.employees.build         # => <Employee id: nil, department_id: nil>

empl.company   # => Employee#company delegated to department.company, but department is nil

我正在使用 Rails 3.2.15。我明白这里发生了什么，我也明白为什么 empl.department_id 为零；尽管我希望 Rails 在调用 save 之前保留对预期关联的直接引用，以便最后一行可以通过未保存的部门对象进行委托。有干净的解决办法吗？

更新：我也在 Rails 4 中尝试过这个，这里是一个控制台会话：

2.0.0-p247 :001 > company = Company.find(1)
  Company Load (1.5ms)  SELECT "companies".* FROM "companies" WHERE "companies"."id" = ? LIMIT 1  [["id", 1]]
 => #<Company id: 1, name: nil, created_at: "2013-10-24 03:36:11", updated_at: "2013-10-24 03:36:11"> 
2.0.0-p247 :002 > dept = company.departments.build
 => #<Department id: nil, name: nil, company_id: 1, created_at: nil, updated_at: nil> 
2.0.0-p247 :003 > empl = dept.employees.build
 => #<Employee id: nil, name: nil, department_id: nil, created_at: nil, updated_at: nil> 
2.0.0-p247 :004 > empl.company
RuntimeError: Employee#company delegated to department.company, but department is nil: #<Employee id: nil, name: nil, department_id: nil, created_at: nil, updated_at: nil>
2.0.0-p247 :005 > empl.department
 => nil 

更新2：这是一个github上的测试项目 https://github.com/dissolved/activerecord_deep_obj_linking.

请查看:inverse_of选项belongs_to http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#method-i-belongs_to and has_many http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#method-i-has_many。在不同情况下构建和获取关联记录时，此选项将处理双向分配。

From 双向关联 http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#label-Bi-directional+associations for ActiveRecord::Associations::ClassMethods在文档中：

指定:inverse_of关联选项可以让您告诉 Active Record 有关反向关系的信息，并且它将优化对象加载。