Merge pull request #21 from silverstripe-rebelalliance/fix/not_indexing_tableless_classes

FIX Throw error if trying to add a table-less DataObject class to index

code/search/SearchIndex.php

@@ -187,6 +187,10 @@ abstract class SearchIndex extends ViewableData {
 			throw new Exception('Can\'t add class to Index after fields have already been added');
 		}
 
+		if (!DataObject::has_own_table($class)) {
+			throw new InvalidArgumentException('Can\'t add classes which don\'t have data tables (no $db or $has_one set on the class)');
+		}
+
  		$options = array_merge(array(
 			'include_children' => true
 		), $options);