From 8a2417a750ede29d4d4c5cb7db984a0d284027fd Mon Sep 17 00:00:00 2001
From: UndefinedOffset <echipman@webbuildersgroup.com>
Date: Thu, 13 Dec 2018 14:05:12 -0400
Subject: [PATCH] Fixed functionality when using ManyManyThroughList

---
 src/Forms/GridFieldSortableRows.php | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/Forms/GridFieldSortableRows.php b/src/Forms/GridFieldSortableRows.php
index 3b55fc7..1d9c7ab 100644
--- a/src/Forms/GridFieldSortableRows.php
+++ b/src/Forms/GridFieldSortableRows.php
@@ -22,6 +22,7 @@ use SilverStripe\ORM\DataObjectSchema;
 use SilverStripe\ORM\DataQuery;
 use SilverStripe\ORM\DB;
 use SilverStripe\ORM\ManyManyList;
+use SilverStripe\ORM\ManyManyThroughList;
 use SilverStripe\ORM\RelationList;
 use SilverStripe\ORM\SS_List;
 use SilverStripe\ORM\UnsavedRelationList;
@@ -231,8 +232,13 @@ class GridFieldSortableRows implements GridField_HTMLProvider, GridField_ActionP
 
         $many_many = ($list instanceof ManyManyList);
         if (!$many_many) {
-            $sng = singleton($gridField->getModelClass());
-            $fieldType = $sng->config()->db[$this->sortColumn];
+            if($list instanceof ManyManyThroughList) {
+                $fieldType = $list->getExtraFields();
+                $fieldType = $fieldType[$this->sortColumn];
+            } else {
+                $sng = singleton($gridField->getModelClass());
+                $fieldType = $sng->config()->db[$this->sortColumn];
+            }
 
             if (!$fieldType || !($fieldType == 'Int' || $fieldType == 'SilverStripe\\ORM\\FieldType\\DBInt' || is_subclass_of($fieldType, 'SilverStripe\\ORM\\FieldType\\DBInt'))) {
                 if (is_array($fieldType)) {