Add trait for dbo collections with cover photos.

wcfsetup/install/files/lib/data/TCollectionCoverPhotos.class.php

@@ -0,0 +1,72 @@
+<?php
+
+namespace wcf\data;
+
+use wcf\data\file\FileList;
+use wcf\data\file\thumbnail\FileThumbnailList;
+use wcf\system\image\cover\photo\FileCoverPhoto;
+
+/**
+ * Trait for dbo collections with cover photos.
+ *
+ * @author      Marcel Werk
+ * @copyright   2001-2025 WoltLab GmbH
+ * @license     GNU Lesser General Public License <http://opensource.org/licenses/lgpl-license.php>
+ * @since       6.3
+ */
+trait TCollectionCoverPhotos
+{
+    /**
+     * @var array<int, FileCoverPhoto>
+     */
+    private array $coverPhotos;
+
+    public function getCoverPhoto(
+        DatabaseObject $object,
+        string $coverPhotoIdProperty = 'coverPhotoFileID',
+    ): ?FileCoverPhoto {
+        $this->loadCoverPhotos($coverPhotoIdProperty);
+
+        return $this->coverPhotos[$object->{$coverPhotoIdProperty}] ?? null;
+    }
+
+    private function loadCoverPhotos(string $coverPhotoIdProperty): void
+    {
+        if (isset($this->coverPhotos)) {
+            return;
+        }
+
+        $this->coverPhotos = [];
+        $coverPhotoIDs = $this->getCoverPhotoIDs($coverPhotoIdProperty);
+        if ($coverPhotoIDs === []) {
+            return;
+        }
+
+        $fileList = new FileList();
+        $fileList->setObjectIDs($coverPhotoIDs);
+        $fileList->readObjects();
+        $files = $fileList->getObjects();
+
+        $thumbnailList = new FileThumbnailList();
+        $thumbnailList->getConditionBuilder()->add("fileID IN (?)", [$fileList->getObjectIDs()]);
+        $thumbnailList->readObjects();
+        foreach ($thumbnailList as $thumbnail) {
+            $files[$thumbnail->fileID]->addThumbnail($thumbnail);
+        }
+
+        $this->coverPhotos = \array_map(fn($file) => new FileCoverPhoto($file), $files);
+    }
+
+    /**
+     * @return int[]
+     */
+    private function getCoverPhotoIDs(string $coverPhotoIdProperty): array
+    {
+        \assert($this instanceof DatabaseObjectCollection);
+
+        return \array_map(
+            static fn(DatabaseObject $object) => $object->{$coverPhotoIdProperty},
+            \array_filter($this->getObjects(), static fn(DatabaseObject $object) => $object->{$coverPhotoIdProperty} !== null)
+        );
+    }
+}