silverstripe-blog/code/compat/tasks/BlogMigrationTask.php

<?php

class BlogMigrationTask extends MigrationTask {
	/**
	 * Should this task be invoked automatically via dev/build?
	 *
	 * @config
	 *
	 * @var bool
	 */
	private static $run_during_dev_build = true;

	/**
	 * {@inheritdoc}
	 */
	public function up() {
		$classes = ClassInfo::implementorsOf('MigratableObject');

		$this->message('Migrating legacy blog records');

		foreach($classes as $class) {
				
				$this->upClass($class);
			}
		
	}

	/**
	 * @param string $text
	 */
	protected function message($text) {
		if(Controller::curr() instanceof DatabaseAdmin) {
			DB::alteration_message($text, 'obsolete');
		} else {
			echo $text . "<br/>";
		}
	}

	/**
	 * Migrate records of a single class
	 *
	 * @param string $class
	 * @param null|string $stage
	 */
	protected function upClass($class) {
		if(!class_exists($class)) {
			return;
		}

		if(is_subclass_of($class, 'SiteTree')) {
			$items = SiteTree::get()->filter('ClassName', $class);
		} else {
			$items = $class::get();
		}

		if($count = $items->count()) {
			$this->message(
				sprintf(
					'Migrating %s legacy %s records.',
					$count,
					$class
				)
			);

			foreach($items as $item) {
				$cancel = $item->extend('onBeforeUp');

				if($cancel && min($cancel) === false) {
					continue;
				}

				/**
				 * @var MigratableObject $item
				 */
				$result = $item->up();
				$this->message($result);

				$item->extend('onAfterUp');
			}
		}
	}

	/**
	 * {@inheritdoc}
	 */
	public function down() {
		$this->message('BlogMigrationTask::down() not implemented');
	}
}