FIX Add eagerloaded data to ALL relevant lists (#11139)

src/ORM/DataList.php

@@ -1372,7 +1372,7 @@ private function addEagerLoadedDataToParent(
                 if ($parentData->hasID($parentID)) {
                     $parentData->addEagerLoadedData($relationName, $parentID, $eagerLoadedData);
                     $added = true;
-                    break;
+                    // can't break here, because the parent might be in multiple relation lists
                 }
             } else {
                 throw new LogicException("Invalid parent for eager loading $relationType relation $relationName");

src/ORM/EagerLoadedList.php

@@ -940,7 +940,7 @@ private function setDataObjectEagerLoadedData(int $id, DataObject $item): void
 
     /**
      * Gets the final rows for this list after applying all transformations.
-     * Currently only limit is applied lazily, but others could be done this was as well.
+     * Currently only limit and sort are applied lazily, but filter could be done this was as well in the future.
      */
     private function getFinalisedRows(): array
     {

tests/php/ORM/DataListEagerLoadingTest.php

@@ -1254,4 +1254,39 @@ public function testLastHasEagerloadedRelation()
         $obj = EagerLoadObject::get()->eagerLoad('HasManyEagerLoadObjects')->last();
         $this->assertInstanceOf(EagerLoadedList::class, $obj->HasManyEagerLoadObjects());
     }
+
+    /**
+     * Tests that if the same record exists in multiple relations, its data is
+     * eagerloaded without extra unnecessary queries.
+     */
+    public function testEagerLoadingSharedRelations()
+    {
+        $record1 = EagerLoadObject::create(['Title' => 'My obj1']);
+        $record1->write();
+        $record2 = EagerLoadObject::create(['Title' => 'My obj2']);
+        $record2->write();
+        $manyMany = ManyManyEagerLoadObject::create(['Title' => 'My manymany']);
+        $manyMany->write();
+        $record1->ManyManyEagerLoadObjects()->add($manyMany);
+        $record2->ManyManyEagerLoadObjects()->add($manyMany);
+        $subManyMany = ManyManySubEagerLoadObject::create(['Title' => 'My submanymany']);
+        $subManyMany->write();
+        $manyMany->ManyManySubEagerLoadObjects()->add($subManyMany);
+
+        $eagerLoadQuery = EagerLoadObject::get()
+            ->filter(['ID' => [$record1->ID, $record2->ID]])
+            ->eagerLoad('ManyManyEagerLoadObjects.ManyManySubEagerLoadObjects');
+        $loop1Count = 0;
+        $loop2Count = 0;
+        foreach ($eagerLoadQuery as $record) {
+            $loop1Count++;
+            $eagerLoaded1 = $record->ManyManyEagerLoadObjects();
+            $this->assertInstanceOf(EagerLoadedList::class, $eagerLoaded1);
+            foreach ($eagerLoaded1 as $manyManyRecord) {
+                $loop2Count++;
+                $eagerLoaded2 = $manyManyRecord->ManyManySubEagerLoadObjects();
+                $this->assertInstanceOf(EagerLoadedList::class, $eagerLoaded2);
+            }
+        }
+    }
 }