silverstripe-blog/code/extensions/BlogPostFilter.php

<?php

/**
 * This is responsible for filtering only published posts to users who do not have permission to
 * view non-published posts.
 *
 * @package silverstripe
 * @subpackage blog
 */
class BlogPostFilter extends DataExtension {
	/**
	 * Augment queries so that we don't fetch unpublished articles.
	 *
	 * @param SQLQuery $query
	 */
	public function augmentSQL(SQLQuery &$query) {
		$stage = Versioned::current_stage();

		if($stage == 'Live' || !Permission::check('VIEW_DRAFT_CONTENT')) {
			$query->addWhere(sprintf('"PublishDate" < \'%s\'', Convert::raw2sql(SS_Datetime::now())));
		}
	}

	/**
	 * This is a fix so that when we try to fetch subclasses of BlogPost, lazy loading includes the
	 * BlogPost table in its query. Leaving this table out means the default sort order column
	 * PublishDate causes an error.
	 *
	 * @see https://github.com/silverstripe/silverstripe-framework/issues/1682
	 *
	 * @param SQLQuery $query
	 * @param mixed $dataQuery
	 * @param mixed $parent
	 */
	public function augmentLoadLazyFields(SQLQuery &$query, &$dataQuery, $parent) {
		$dataQuery->innerJoin('BlogPost', '"SiteTree"."ID" = "BlogPost"."ID"');
	}
}