Rails：检查多态关系中关联的belongs_to对象类型

Question

我有三个模型：

class Product
  belongs_to :object, polymorphic: true
  belongs_to :membership, foreign_key: :object_id
  belongs_to :ticket, foreign_key: :object_id
end

class Membership
end

class Ticket
end

比如说，我有一个product，它有一个关联的membership。例如。我可以这样做：product.membership 或 product.object

但在这种情况下，我也可以使用product.ticket。

如何确保 Rails 在这种情况下引发错误？

Answer 1

您可能应该看一下this post，其中引用了一些解决此问题的方法。 或许this post 也能帮到你。

这些帖子中列出的解决方案：

• 在 Rails 5.2 上

  belongs_to :membership, -> { includes(:object).where(products: { object_type: Membership.to_s }) }, foreign_key: :object_id
  belongs_to :ticket, -> { includes(:object).where(products: { object_type: Ticket.to_s }) }, foreign_key: :object_id
  

• 在 Rails 4.2 上（但在 6.1 上似乎已弃用，因为不再允许使用 foreign_type）

  belongs_to :membership, -> { where(notes: { object_type: :Membership }) }, foreign_key: :object_id, foreign_type: :Membership, optional: true
  

• 在 Rails 4.1 上

  class Product < ActiveRecord::Base
  # The true polymorphic association
  belongs_to :object, polymorphic: true
  
  # The trick to solve this problem
  has_one :self_ref, :class_name => self, :foreign_key => :id
  
  has_one :membership, :through => :self_ref, :source => :object, :source_type => Membership
  has_one :ticket, :through => :self_ref, :source => :object, :source_type => Ticket