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

class CreatePostVersions < ActiveRecord::Migration[8.0]
  def change
    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

    reversible do |dir|
      dir.up do
        execute <<~SQL
          INSERT INTO
            post_versions(
              post_id
            , version_no
            , event_type
            , title
            , url
            , thumbnail_base
            , tags
            , parent_id
            , original_created_from
            , original_created_before
            , created_at
            , created_by_user_id)
          SELECT
            posts.id
          , 1
          , 'create'
          , posts.title
          , posts.url
          , posts.thumbnail_base
          , COALESCE(tag_snapshots.tags, '')
          , posts.parent_id
          , posts.original_created_from
          , posts.original_created_before
          , posts.created_at
          , posts.uploaded_user_id
          FROM
            posts
            LEFT JOIN
              (
                SELECT
                  post_tags.post_id
                , GROUP_CONCAT(tag_names.name ORDER BY tag_names.name SEPARATOR ' ') AS tags
                FROM
                  post_tags
                  INNER JOIN
                    tags
                    ON
                      tags.id = post_tags.tag_id
                  INNER JOIN
                    tag_names
                    ON
                      tag_names.id = tags.tag_name_id
                WHERE
                  post_tags.discarded_at IS NULL
                GROUP BY
                  post_tags.post_id
                ) tag_snapshots
              ON
                tag_snapshots.post_id = posts.id
        SQL
      end
    end
  end
end