Refactoring for: https://codereview.stackexchange.com/questions/222115/re-creating-user-discounts-nightly

user_discount.rb

class UserDiscount < ApplicationRecord
  belongs_to :user
  belongs_to :discount

  def self.invalid_user_discounts
    UserDiscount.
      joins("INNER JOIN discount_segments ON user_discounts.discount_id = discount_segments.discount_id").
      joins("INNER JOIN user_segments ON user_discounts.user_id = user_segments.user_id").
      where("user_segments.segment_id <> discount_segments.segment_id")
  end

  def self.clean_user_discounts!
    invalid_user_discounts.find_each do |user_discount|
      user_discount.destroy
    end
  end


  # Creates UserDiscounts when a user belongs to a segment and that segment has a discount
  def self.create_user_discounts
    query = UserSegment.
      joins("INNER JOIN discount_segments ON user_segments.segment_id = discount_segments.segment_id").select(:id, :discount_id, :user_id)


    query.find_each do |user_and_discount_segment|
      UserDiscount.find_or_create_by(
        discount_id: user_and_discount_segment.discount_id,
        user_id: user_and_discount_segment.user_id)
    end
  end
end