Question

当我使用has_one时，它可以很好地工作，但不能用于has_many。在这里你可以看到object_id是不同的，因为它运行另一个SQL来再次获取它。

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 >

以下是我用来设置测试的代码：

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

不，不是。根据{{3}}，

他们不使用：通过协会。
他们不兼容：多态关联。
他们不能与：作为协会。
对于belongs_to关联，忽略has_many反向关联。

Answer 2

是的，确实如此！请在此处参考活动记录中关联的API文档的双向关联部分：http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html

Answer 3

在本视频的最后一部分中，有关设置Rails 5模型的示例，其中有一个示例，说明has_many关系如何在没有，然后使用inverse_of。编写RSpec测试以确认object_ids实际上是相同的：

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

inverse_of与has_many一起使用吗？

3 个答案: