btrc-hub/backend/db/migrate/20260409123700_create_post_versions.rb

class CreatePostVersions < ActiveRecord::Migration[8.0]
  class Post < ApplicationRecord
    self.table_name = 'posts'
  end

  class PostTag < ApplicationRecord
    self.table_name = 'post_tags'
  end

  class PostVersion < ApplicationRecord
    self.table_name = 'post_versions'
  end

  def up
    create_table :post_versions do |t|
      t.references :post, null: false, foreign_key: true
      t.integer :version_no, null: false
      t.string :event_type, null: false
      t.string :title
      t.string :url, limit: 768, null: false
      t.string :thumbnail_base, limit: 2000
      t.text :tags, null: false
      t.references :parent, foreign_key: { to_table: :posts }
      t.datetime :original_created_from
      t.datetime :original_created_before
      t.datetime :created_at, null: false
      t.references :created_by_user, foreign_key: { to_table: :users }

      t.index [:post_id, :version_no], unique: true
      t.check_constraint 'version_no > 0'
      t.check_constraint "event_type IN ('create', 'update', 'discard', 'restore')"
    end

    say_with_time 'Backfilling post_versions' do
      Post.find_in_batches(batch_size: 500) do |posts|
        post_ids = posts.map(&:id)

        tag_names_by_post_id =
            PostTag
            .joins('INNER JOIN tags ON tags.id = post_tags.tag_id')
            .joins('INNER JOIN tag_names ON tag_names.id = tags.tag_name_id')
            .where(post_id: post_ids)
            .where('post_tags.discarded_at IS NULL')
            .where('tags.discarded_at IS NULL')
            .where('tag_names.discarded_at IS NULL')
            .pluck('post_tags.post_id', 'tag_names.name')
            .each_with_object(Hash.new { |h, k| h[k] = [] }) do |(post_id, tag_name), h|
              h[post_id] << tag_name
            end

        rows = posts.map do |post|
          tags = tag_names_by_post_id[post.id].uniq.sort.join(' ')
          { post_id: post.id,
            version_no: 1,
            event_type: 'create',
            title: post.title,
            url: post.url,
            thumbnail_base: post.thumbnail_base,
            tags:,
            parent_id: post.parent_id,
            original_created_from: post.original_created_from,
            original_created_before: post.original_created_before,
            created_at: post.created_at,
            created_by_user_id: post.uploaded_user_id }
        end

        PostVersion.insert_all!(rows) if rows.present?
      end
    end
  end

  def down
    drop_table :post_versions
  end
end