function sync_course_with_contents( $course_ID = 0 ) {
		global $wpdb;

		do_action( 'dozent_course/sync_course_with_contents/before', $course_ID );

		$sections = dozent_db_query_get_sections( $course_ID );

		$lecture_count     = 0;
		$quiz_count        = 0;
		$assignment_count  = 0;
		$attachments_count = 0;
		$total_video_time  = 0;
		$content_ids = [];

		if ( dozent_count( $sections ) ) {

			foreach ( $sections as $section ) {

				$total_lectures_in_section = 0;
				$contents                  = dozent_get_course_contents_by_section( $section->ID );

				if ( dozent_count( $contents->posts ) ) {
					foreach ( $contents->posts as $post ) {

						$content_ids[] = $post->ID;

						if ( $post->post_type === 'dozent_lecture' ) {

							$total_lectures_in_section ++;
							$lecture_count ++;

							$lecture_video_time = video_runtime_to_seconds( $post->ID );
							$total_video_time   = $total_video_time + $lecture_video_time;

						} elseif ( $post->post_type === 'dozent_quiz' ) {
							$quiz_count ++;
						} elseif ( $post->post_type === 'dozent_assignment' ) {
							$assignment_count ++;
						}
					}
				}

				update_post_meta( $section->ID, '_total_lectures', $total_lectures_in_section );

			}
		}

		/**
		 * Get total Attachments and count them.
		 */

		$content_ids = array_filter( $content_ids );
		if ( dozent_count( $content_ids ) ) {
			$content_ids = implode( ',', array_map( 'absint', $content_ids ) );
			$content_attachments
			             = $wpdb->get_col( "SELECT meta_value FROM {$wpdb->postmeta} where meta_key = '_attachments' AND post_id IN({$content_ids}) " );

			if ( dozent_count( $content_attachments ) ) {
				foreach ( $content_attachments as $content_attachment ) {
					$content_attachment        = (array) maybe_unserialize( $content_attachment );
					$content_attachment        = array_filter( $content_attachment );
					$content_attachments_count = dozent_count( $content_attachment );

					if ( $content_attachments_count ) {
						$attachments_count = $attachments_count + $content_attachments_count;
					}

				}
			}
		}

		update_post_meta( $course_ID, '_total_lectures', $lecture_count );
		update_post_meta( $course_ID, '_total_quiz', $quiz_count );
		update_post_meta( $course_ID, '_total_assignments', $assignment_count );
		update_post_meta( $course_ID, '_total_attachments', $attachments_count );
		update_post_meta( $course_ID, '_total_video_time', $total_video_time );

		//Delete course cache contents
		wp_cache_delete( $course_ID, 'dozent_course_contents' );

		do_action( 'dozent_course/sync_course_with_contents/after', $course_ID );

	}