rails HABTM to has many through

Question

class QuestionSet
  has_and_belongs_to_many :questions,
                      class_name: 'Exam',
                      join_table: 'question_question_sets',
                      foreign_key: 'question_set_id',
                      association_foreign_key: 'question_id'
end
class Question
  has_and_belongs_to_many :question_sets,
                      class_name: 'Exam',
                      join_table: 'question_question_sets',
                      foreign_key: 'question_id',
                      association_foreign_key: 'question_set_id'
end

上述模型是从基本模型Exam（使用Rails STI）继承的，并且联接表包含两个字段：question_id和question_set_id。现在我需要将此关联转换为has_many through。

我尝试如下：

class QuestionQuestionSet
  has_many :questions
  has_many :question_sets 
end
class Question
  has_many :question_question_sets, foreign_key: :question_id
  has_many :question_sets, through: :question_question_sets 
end
class QuestionSet
  has_many :question_question_sets, foreign_key: :question_set_id
  has_many :questions, through: :question_question_sets 
end

Answer 1

即使在编辑模型后，也必须创建一个新的加入表，因为上一个（由HABTM创建）没有和" ID"列。作为参考，您可以按照http://www.chrisrolle.com/en/blog/migration-path-path-from-habtm-habtm-to-has_many-though