Associations and (multiple) foreign keys in rails (3.2) : how to describe them in the model, and write up migrations

Question

I have 3 models: Question, Option, Rule

Question has_many options; Option needs a foreign key for question_id

Rule table consists of 3 foreign_keys:

Answer 1

Note: I have found this way to solve the problem.Kindness from China.

If you have RailsAdmin with you,you may notice that you can see all rules of one question as long as one field of both question fields(assumption_question_id,consequent_question_id) equals to id of the question.

I have done detailed test on this and found out that Rails always generates a condition "question_id = [current_id]" which make to_sql outputs

SELECT `rules`.* FROM `rules` WHERE `rules`.`question_id` = 170

And the reason that the following model

class Question < ActiveRecord::Base
  has_many :options
  # Notice ↓
  has_many :rules, ->(question) { where("assumption_question_id = ? OR consequent_question_id = ?", question.id, question.id) }, class_name: 'Rule'
  # Notice ↑
end

makes Question.take.rules.to_sql be like this

SELECT `rules`.* FROM `rules` WHERE `rules`.`question_id` = 170 AND (assumption_question_id = 170 OR consequent_question_id = 170)

Is that we have not yet get ride of the annoy question_id so no matter how we describe or condition properly, our condition follows that "AND".

Then,we need to get ride of it.How?

Click here and you will know how,Find sector 8.1,and you can see

Article.where(id: 10, trashed: false).unscope(where: :id)
# SELECT "articles".* FROM "articles" WHERE trashed = 0

Then lets do it:

class Question < ActiveRecord::Base
  has_many :options
  # Notice ↓
  has_many :rules, ->(question) { unscope(where: :question_id).where("assumption_question_id = ? OR consequent_question_id = ?", question.id, question.id) }, class_name: 'Rule'
  # Notice ↑
end

class Rule < ActiveRecord::Base
  belongs_to :option
  belongs_to :assumption_question, class_name: "Question", foreign_key: :assumption_question_id, inverse_of: :assumption_rules
  belongs_to :consequent_question, class_name: "Question", foreign_key: :consequent_question_id, inverse_of: :consequent_rules
end

class Option < ActiveRecord::Base
  belongs_to :question
  has_one    :rule
end

All done.

Finally

This is my first answer here at stackoverflow,and this method is never found anywhere else.

Thanks for reading.