こんな感じ。
DB::beginTransaction();
try {
$blog = Blog::find($id);
$blog->comments()->detach();
$blog->delete();
DB::commit();
$success = true;
} catch (\Exception $e) {
$success = false;
DB::rollback();
}
【参考】
http://programmer-jobs.blogspot.jp/2017/02/laravel-5-4-database-transactions.html