Normalize class_names for attachments migrated from legacy Part-DB database

This fixes issue #272

migrations/Version20230417211732.php

@@ -0,0 +1,51 @@
+<?php
+
+declare(strict_types=1);
+
+namespace DoctrineMigrations;
+
+use App\Migration\AbstractMultiPlatformMigration;
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+/**
+ * Auto-generated Migration: Please modify to your needs!
+ */
+final class Version20230417211732 extends AbstractMultiPlatformMigration
+{
+    public function getDescription(): string
+    {
+        return 'Fix class names in attachments table for databases migrated from legacy Part-DB';
+    }
+
+    public function mySQLUp(Schema $schema): void
+    {
+        //Delete all attachments where the corresponding part or device was deleted in legacy Part-DB (and therefore does not exist in the new Part-DB
+        $this->addSql('DELETE FROM attachments WHERE class_name = "PartDB\\\\Part" AND NOT EXISTS (SELECT id FROM parts WHERE id = attachments.element_id)');
+        $this->addSql('DELETE FROM attachments WHERE class_name = "PartDB\\\\Device" AND NOT EXISTS (SELECT id FROM projects WHERE id = attachments.element_id)');
+
+        // Replace all attachments where class_name is the legacy "PartDB\Part" with the new version "Part"
+        //We have to use 4 backslashes here, as PHP reduces them to 2 backslashes, which MySQL interprets as an escaped backslash.
+        $this->addSql('UPDATE attachments SET class_name = "Part" WHERE class_name = "PartDB\\\\Part"');
+        //Do the same with PartDB\Device and Device
+        $this->addSql('UPDATE attachments SET class_name = "Device" WHERE class_name = "PartDB\\\\Device"');
+
+
+    }
+
+    public function mySQLDown(Schema $schema): void
+    {
+        // We can not revert this migration, because we don't know the old class name.
+    }
+
+    public function sqLiteUp(Schema $schema): void
+    {
+        //As legacy database can only be migrated to MySQL, we don't need to implement this method.
+        $this->skipIf(true, 'Not needed for SQLite');
+    }
+
+    public function sqLiteDown(Schema $schema): void
+    {
+        //As we done nothing, we don't need to implement this method.
+    }
+}