ruby-on-rails - Rails has_many :through validation nested records count by specific param

Question

我有模型 Workout 和 User，它们通过模型关联了很多 用户锻炼。模型 UserWorkout 有属性 :is_creator，显示哪个用户是创建者。但是 Workout 应该只有一个创建者。添加此类验证的最佳方式是什么？

 class Workout < ActiveRecord::Base

  has_many :user_workouts, inverse_of: :workout, dependent: :destroy
  has_many :participants, through: :user_workouts, source: :user

  def creator
    participants.where(user_workouts: { is_creator: true }).order('user_workouts.created_at ASC').first
  end

end

class UserWorkout < ActiveRecord::Base

  belongs_to :user
  belongs_to :workout

end

class User < ActiveRecord::Base

  has_many :user_workouts, inverse_of: :user, dependent: :destroy
  has_many :workouts, through: :user_workouts

end

Answer 1

根据您的 DBMS，您可以添加 filtered/partial index在 workout_id where is_creator = true

上

在事件记录级别，您可以添加 custom validation

class UserWorkout
  validate :workout_has_only_one_creator

  private

  def workout_has_only_one_creator
    if self.class.find_by(workout_id: workout_id, is_creator: true)
      errors.add(:is_creator, 'can only have one creator')
    end
  end