silverstripe-blog/extensions/BlogPostFilter.php

<?php

class BlogPostFilter extends DataExtension {

	/**
	 * Augment queries so that we don't fetch unpublished articles.
	**/
	public function augmentSQL(SQLQuery &$query) {

		if(!Permission::check("VIEW_DRAFT_CONTENT")) {
			$stage = Versioned::current_stage();
			if($stage == "Stage") $stage = "";
			else $stage = "_" . Convert::raw2sql($stage);

			$query->addWhere("PublishDate < NOW()");
		}

	}

}