kekec_bbs_v2/backend/app/models/post.rb

class Post < ApplicationRecord
  belongs_to :thread, class_name: 'Topic', foreign_key: :thread_id
  has_one_attached :image

  before_create :set_post_no

  has_secure_password validations: false

  scope :active, -> { where deleted_at: nil }

  private

  def set_post_no
    max_no = Post.where(thread_id:).maximum(:post_no) || 0
    self.post_no = max_no + 1
  end
end