Rails has_many：through：多态关系调用错误

Question

我有has_many：通过：某些模型之间的多态关系：

class Tagging < ActiveRecord::Base
  belongs_to :tag
  belongs_to :tagging, :polymorphic => true
end

class Tag < ActiveRecord::Base
  has_many :taggings
  has_many :recipes,    through: :taggings, source: :taggable, source_type: 'Recipe', dependent: :destroy
end

class Recipe < ActiveRecord::Base
  has_many :taggings, as: :taggable
  has_many :tags, through: :taggings, dependent: :destroy
end

当我输入Tag.first.recipes时出现以下错误：

  

SELECT＆＃34; tags＆＃34;。* FROM＆＃34; tags＆＃34; ORDER BY＆＃34;标签＆＃34;。＆＃34; id＆＃34; DESC限制1   ActiveRecord :: HasManyThroughSourceAssociationNotFoundError：无法在模型标记中找到源关联：taggable。尝试'has_many：recipes，：through =＆gt; ：taggings，：source =＆gt; ＆＃39 ;.它是标记还是标记之一？

有什么想法吗？