Weak hands cannot be planted, meager skills have no foundation. Shallow wisdom is futile, how can one hope for a good name?扰扰从役倦，屑屑身事微。少壮轻年月，迟暮惜光辉。
add_column(
$this->get_table_name(),
'object_last_modified',
'datetime',
[
'null' => true,
'default' => null,
],
);
$this->add_column(
$this->get_table_name(),
'object_published_at',
'datetime',
[
'null' => true,
'default' => null,
],
);
$this->add_index(
$this->get_table_name(),
[
'object_published_at',
'is_robots_noindex',
'object_type',
'object_sub_type',
],
[
'name' => 'published_sitemap_index',
],
);
}
/**
* Migration down.
*
* @return void
*/
public