class BlogPost extends DataObject {
	static $many_many = array(
		'BlogTags' => 'BlogTag'
	);
}

class BlogTag extends DataObject {
	static $db = array(
		'Title' => 'Varchar(200)',
	);

	static $belongs_many_many = array(
		'BlogPosts' => 'BlogPost'
	);
}

$field = TagField::create(
		'BlogTags', 'Blog Tags', BlogTag::get(), $post->BlogTags()
	)->setShouldLazyLoad(true) // tags should be lazy loaded
	->setCanCreate(true);      // new tag DataObjects can be created

class BlogPost extends DataObject {
	static $db = array(
		'Tags' => 'Text'
	);
}

$field =  StringTagField::create(
	'BlogTags', 'Blog Tags', array('one', 'two'), explode(',', $post->Tags)
);

$field->setShouldLazyLoad(true); // tags should be lazy loaded