inverse_of是否適用於has_many？

Question

當我使用has_one時，它完美地工作，但不是在has_many上。在這裏你可以看到object_id是不同的，因爲它運行另一個SQL來再次獲取它。

ruby-1.9.2-p290 :001 > e = Employee.create(name: 'rafael', active: false) 
ruby-1.9.2-p290 :002 > b = Badge.create(number: 1, employee: e) 
ruby-1.9.2-p290 :003 > a = Address.create(street: "123 Market St", city: "San Diego", employee: e) 
ruby-1.9.2-p290 :004 > e = Employee.first 
    Employee Load (0.2ms) SELECT "employees".* FROM "employees" LIMIT 1 
=> #<Employee id: 1, name: "rafael", active: false, created_at: "2011-10-04 17:09:25", updated_at: "2011-10-04 17:09:25"> 
ruby-1.9.2-p290 :002 > e.is_active? 
=> false 
ruby-1.9.2-p290 :003 > e.object_id 
=> 2182895380 
ruby-1.9.2-p290 :004 > e.badge.employee.is_active? 
    Badge Load (17.6ms) SELECT "badges".* FROM "badges" WHERE "badges"."employee_id" = 1 LIMIT 1 
=> false 
ruby-1.9.2-p290 :005 > e.badge.employee.object_id 
=> 2182895380 
ruby-1.9.2-p290 :006 > e.addresses.first.employee.is_active? 
    Address Load (0.2ms) SELECT "addresses".* FROM "addresses" WHERE "addresses"."employee_id" = 1 LIMIT 1 
    Employee Load (0.3ms) SELECT "employees".* FROM "employees" WHERE "employees"."id" = 1 LIMIT 1 
=> false 
ruby-1.9.2-p290 :007 > e.addresses.first.employee.object_id 
    Address Load (0.3ms) SELECT "addresses".* FROM "addresses" WHERE "addresses"."employee_id" = 1 LIMIT 1 
    Employee Load (0.2ms) SELECT "employees".* FROM "employees" WHERE "employees"."id" = 1 LIMIT 1 
=> 2181302220 
ruby-1.9.2-p290 :008 > 

這裏是我設置用我的測試代碼：

class Employee < ActiveRecord::Base 
    has_many :addresses, :inverse_of => :employee 
    has_one :badge, :inverse_of => :employee 

    accepts_nested_attributes_for :addresses 
    accepts_nested_attributes_for :badge 
    # validates_associated :addresses 

    def is_active? 
    active 
    end 
end 

class Address < ActiveRecord::Base 
    belongs_to :employee, :inverse_of => :addresses 

    validates :city, length: { within: 100..1000, message: "Too short"}, :if => lambda {|a| a.employee.is_active?} 
end 

class Badge < ActiveRecord::Base 
    belongs_to :employee, :inverse_of => :badge 

    validates :number, length: { within: 2..10, message: "Too long"}, :if => lambda {|b| b.employee.is_active?} 
end 

Answer 1

是它！請參閱活動記錄中關聯API文檔的雙向關聯部分：http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html

Answer 2

不，它不是。根據Rails Guide，

• 他們不適用於：通過關聯。
• 它們不適用於：多態關聯。
• 他們不與：作爲協會。
• 對於belongs_to關聯，忽略has_many反向關聯。

Answer 3

在這段關於設置Rails 5模型的視頻的最後部分，有一個has_many關係如何運行的例子，然後是inverse_of。一個RSpec測試寫入確認object_ids其實都是一樣的：

https://www.youtube.com/watch?v=5sfufoY59Ek&feature=youtu.be&t=42m54s