FIX Trigger eagerloading for first() and last()

src/ORM/DataList.php

@@ -1408,8 +1408,13 @@ public function sum($fieldName)
      */
     public function first()
     {
-        foreach ($this->dataQuery->firstRow()->execute() as $row) {
-            return $this->createDataObject($row);
+        // We need to trigger eager loading by iterating over the list, rather than just fetching
+        // the first row from the dataQuery.
+        // This limit and offset logic mimics that $this->dataQuery->firstRow() would ultimately do.
+        $limitOffset = $this->dataQuery->query()->getLimit() ?? [];
+        $offset =  array_key_exists('start', $limitOffset) ? $limitOffset['start'] : 0;
+        foreach ($this->limit(1, $offset) as $record) {
+            return $record;
         }
         return null;
     }
@@ -1423,8 +1428,14 @@ public function first()
      */
     public function last()
     {
-        foreach ($this->dataQuery->lastRow()->execute() as $row) {
-            return $this->createDataObject($row);
+        // We need to trigger eager loading by iterating over the list, rather than just fetching
+        // the last row from the dataQuery.
+        // This limit and offset logic mimics that $this->dataQuery->lastRow() would ultimately do.
+        $limitOffset = $this->dataQuery->query()->getLimit() ?? [];
+        $offset =  array_key_exists('start', $limitOffset) ? $limitOffset['start'] : 0;
+        $index = max($this->count() + $offset - 1, 0);
+        foreach ($this->limit(1, $index) as $record) {
+            return $record;
         }
         return null;
     }

tests/php/ORM/DataListEagerLoadingTest.php

@@ -4,6 +4,7 @@
 
 use InvalidArgumentException;
 use SilverStripe\Dev\SapphireTest;
+use SilverStripe\ORM\ArrayList;
 use SilverStripe\ORM\DataList;
 use SilverStripe\ORM\DataObject;
 use SilverStripe\ORM\DB;
@@ -1115,4 +1116,22 @@ public function provideEagerLoadingEmptyRelationLists(): array
             ],
         ];
     }
+
+    public function testFirstHasEagerloadedRelation()
+    {
+        $record = EagerLoadObject::create(['Title' => 'My obj']);
+        $record->write();
+        $record->HasManyEagerLoadObjects()->add(HasManyEagerLoadObject::create(['Title' => 'My related obj']));
+        $obj = EagerLoadObject::get()->eagerLoad('HasManyEagerLoadObjects')->first();
+        $this->assertInstanceOf(ArrayList::class, $obj->HasManyEagerLoadObjects());
+    }
+
+    public function testLastHasEagerloadedRelation()
+    {
+        $record = EagerLoadObject::create(['Title' => 'My obj']);
+        $record->write();
+        $record->HasManyEagerLoadObjects()->add(HasManyEagerLoadObject::create(['Title' => 'My related obj']));
+        $obj = EagerLoadObject::get()->eagerLoad('HasManyEagerLoadObjects')->last();
+        $this->assertInstanceOf(ArrayList::class, $obj->HasManyEagerLoadObjects());
+    }
 }

tests/php/ORM/DataListTest.php

@@ -2081,6 +2081,28 @@ public function testColumnFromRelatedTable()
         ], $productTitles);
     }
 
+    public function testFirst()
+    {
+        $list = Sortable::get()->sort('Sort');
+        $this->assertGreaterThanOrEqual(
+            3,
+            $list->count(),
+            'We must have at least 3 items for this test to be valid'
+        );
+        $this->assertSame('Steve', $list->first()->Name);
+    }
+
+    public function testLast()
+    {
+        $list = Sortable::get()->sort('Sort');
+        $this->assertGreaterThanOrEqual(
+            3,
+            $list->count(),
+            'We must have at least 3 items for this test to be valid'
+        );
+        $this->assertSame('John', $list->last()->Name);
+    }
+
     public function testChunkedFetch()
     {
         $expectedIDs = Team::get()->map('ID', 'ID')->toArray();