如何将sql查询更改为活动记录（ROR）？

Question

这是我的SQL查询：

  

从answer_histories INNER JOIN中选择answer_histories。*   material_progresses ON material_progresses.id =   answer_histories.material_progress_id INNER JOIN learning_histories   在learning_histories.id = answer_histories.learning_history_id和   learning_histories.deleted_at是NULL和   learning_histories.completed_at IS NOT NULL where   answer_histories.deleted_at IS为NULL，answer_histories.slide_id = 3   和material_progresses.site_id = 1和learning_histories.id IN   （SELECT MAX（learning_histories.id）FROM learning_histories WHERE   learning_histories.completed_at IS NOT NULL GROUP BY   learning_histories.material_progress_id）;

我已经做了一些事情。但是失败了

我的learning_history.rb

> class LearningHistory < ActiveRecord::Base   extend Enumerize  
> acts_as_paranoid   records_with_operator_on :create, :update, :destroy
> belongs_to :material_progress   has_many :answer_histories   scope
> :completed, ->{ where.not(completed_at: nil) }   enumerize :status,
>     :in => [:not_attempted, :incomplete, :completed, :failed, :passed, :browsed],
>     :default => :not_attempted   after_create :update_material_progress   after_save :reset_material_progress, :if
> => :reset?   def completed?
>     [:completed, :failed, :passed].include?(status.try(:to_sym))   end    end end