Example of my versioning problem from earlier, or: things that were easier before ORMs

01_versioned.sql

CREATE TABLE items (
  uuid VARCHAR(255) NOT NULL PRIMARY KEY,
  name VARCHAR(255) NOT NULL DEFAULT '');

CREATE TABLE item_versions (
  uuid VARCHAR(255) NOT NULL PRIMARY KEY,
  version INT(64) NOT NULL UNIQUE AUTO_INCREMENT,
  updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP);

INSERT INTO items(uuid, name) VALUES("APP_GENERATED_ID", "An item");
REPLACE INTO item_versions SET uuid = "APP_GENERATED_ID";

SELECT items.*, item_versions.version FROM items, item_versions WHERE items.uuid = item_versions.uuid ORDER BY version DESC;

INSERT INTO items(uuid, name) VALUES("e2ee6f5c-c096-11e1-81de-966c5e8fb5dd", "Another item");
REPLACE INTO item_versions SET uuid = "e2ee6f5c-c096-11e1-81de-966c5e8fb5dd";

UPDATE items SET name = "Updated name" WHERE uuid = 'APP_GENERATED_ID';
REPLACE INTO item_versions SET uuid = "APP_GENERATED_ID";

SELECT items.*, item_versions.version FROM items, item_versions WHERE items.uuid = item_versions.uuid ORDER BY version DESC;

02_item.rb

class Item
  self.primary_key = :uuid
  before_create :set_uuid
  after_save :update_version

  private

  def set_uuid
    self.uuid ||= SecureRandom.uuid
  end

  def update_version
    # AFAIK this works in MySQL, would need to be adapted for any other RDBMS
    # FIXME: Not that this is a security hole but surely there's a less
    #   SQL-injecty way to do this
    connection.execute("REPLACE INTO item_versions SET uuid = '#{self.uuid}'")
  end

end