ruby-on-rails - rails : Query parents with grandchildren (associations)

Question

class User < ActiveRecord::Base
  has_many :posts
end

class Question < ActiveRecord::Base
  belongs_to :user
  has_many :answers
end

class Answer < ActiveRecord::Base
  belongs_to :question
end

使用 Rails 我可以:

1.返回所有有问题的用户？例如。

@users_with_questions = User.joins(:question).where.not(question: { id: nil })

2.返回所有用户的answers?

Answer 1

1.返回所有有问题的用户？

@users_with_questions = User.includes(:question).where.not(:question => {id: nil})

2.返回所有用户的答案？

@users_with_answers = User.includes(question: :answer).where.not(:answer => {id: nil})