Merge pull request #75 from briceburg/editable-relfields

 support and cast relationship references as ReadonlyField

Author: nyeholt

code/GridFieldEditableColumns.php

@@ -30,7 +30,8 @@ public function getColumnContent($grid, $record, $col) {
 
 		$fields = $this->getForm($grid, $record)->Fields();
 		$value  = $grid->getDataFieldValue($record, $col);
-		$field  = clone $fields->fieldByName($col);
+		$rel = (strpos($col,'.') === false); // field references a relation value
+		$field = ($rel) ? clone $fields->fieldByName($col) : new ReadonlyField($col);
 
 		if(!$field) {
 			throw new Exception("Could not find the field '$col'");