From 0aa13da0d99a94a0a6dc4cc8cf42e37abcf5374a Mon Sep 17 00:00:00 2001
From: Damian Mooyman <damian@silverstripe.com>
Date: Wed, 6 Jun 2018 09:43:04 +1200
Subject: [PATCH] BUG Backport bugfix for belongs_many_many with many_many
 through. Partial backport of #7928 Fixes #8131

---
 src/ORM/DataObjectSchema.php                   | 14 +++++++++++---
 tests/php/ORM/ManyManyThroughListTest/Item.php |  3 ++-
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/ORM/DataObjectSchema.php b/src/ORM/DataObjectSchema.php
index e309a1660..8251c8477 100644
--- a/src/ORM/DataObjectSchema.php
+++ b/src/ORM/DataObjectSchema.php
@@ -982,9 +982,17 @@ class DataObjectSchema
         if (!$otherManyMany) {
             return null;
         }
-        foreach ($otherManyMany as $inverseComponentName => $nextClass) {
-            if ($nextClass === $parentClass) {
-                return $inverseComponentName;
+        foreach ($otherManyMany as $inverseComponentName => $manyManySpec) {
+            // Normal many-many
+            if ($manyManySpec === $parentClass) {
+                 return $inverseComponentName;
+            }
+            // many-many through, inspect 'to' for the many_many
+            if (is_array($manyManySpec)) {
+                $toClass = $this->hasOneComponent($manyManySpec['through'], $manyManySpec['to']);
+                if ($toClass === $parentClass) {
+                    return $inverseComponentName;
+                }
             }
         }
         return null;
diff --git a/tests/php/ORM/ManyManyThroughListTest/Item.php b/tests/php/ORM/ManyManyThroughListTest/Item.php
index e717b3c84..9f96e7d14 100644
--- a/tests/php/ORM/ManyManyThroughListTest/Item.php
+++ b/tests/php/ORM/ManyManyThroughListTest/Item.php
@@ -19,6 +19,7 @@ class Item extends DataObject implements TestOnly
     ];
 
     private static $belongs_many_many = [
-        'Objects' => 'SilverStripe\\ORM\\Tests\\ManyManyThroughListTest\\TestObject.Items'
+        // Intentionally omit parent `.Items` specifier to ensure it's not mandatory
+        'Objects' => TestObject::class,
     ];
 }