Rails 5中的多态关联事务失败

class User < ApplicationRecord
  has_many :comments, as: :commentable, dependent: :destroy
end

class Article < ApplicationRecord
  has_many :comments, as: :commentable, dependent: :destroy
end

class Comment < ApplicationRecord
  belongs_to :commentable, polymorphic: true

  validates :content, presence: true
end

# 在控制器中保存关联对象
def create_comment
  @commentable = find_commentable
  @comment = @commentable.comments.build(comment_params)

  if @comment.save
    # 保存成功
  else
    # 保存失败，处理错误情况
  end
end

private

def find_commentable
  params.each do |name, value|
    if name =~ /(.+)_id$/
      return $1.classify.constantize.find(value)
    end
  end
  nil
end

def comment_params
  params.require(:comment).permit(:content)
end