Laravel如何使用数据库事务及捕获事务失败后的异

DB::transaction(function () {
 DB::table('users')->update(['votes' => 1]);

 DB::table('posts')->delete();
});

DB::beginTransaction();

DB::rollBack();

DB::mit();

---------------------------------------
id  title    content
--------------------------------------- 

-------------------
id  name
-------------------

----------------------------------
id   tag_id  wiki_id
----------------------------------

<?php

namespace App\Http\Controllers;

use Illuminate\Http\Request;
use Illuminate\Database\QueryException;
use App\Wiki;

class TestController extends Controller
{
 //用DB facade的事务方法控制 查询语句构建器的事务
 public function storeWiki(Request $request)
 {
  DB::beginTransaction();
  try {
   $tagIds = explode(',', $request->get('tag_id'));
   $wiki_id = DB::table('wiki')->insertGetId([
    'title' => $request->get('title'),
    'content' => $request->get('content')
   ]);

   $relationData = [];
   foreach($tagIds as $tagId) {
    $data = ['wiki_id' => $wiki_id, 'tag_id' => $tagId];
    $relationData[] = $data;
   }
   DB::table('wiki_tag_rel')->insert($relationData);
   DB::mit();
  } catch(\Illuminate\Database\QueryException $ex) {
   DB::rollback();
   return \Response::json(['status' => 'error', 'error_msg' => 'Failed, please contact supervisor']);
  }
  
  return \Response::json(['status' => 'ok']);
 }


 //用DB facade的事务方法控制 Eloquent ORM的事务
 public function createWiki(array $data)
 {
  DB::beginTransaction();
  try {
   $tagIds = explode(',', $data['tag_id']);
   $newWiki = Wiki::create([
    'title' => $data['title'],
    'content' => $data['content']
   ]);
   //Wiki和Tag两个Model使用了belongsToMany建立了多对多的关系
   //通过attach方法来附加wiki和tag的关系(写入中间表)
   $newWiki->tags()->attach($tagIds);
   DB::mit();
  } catch(QueryException $ex) {
   DB::rollback();
   return \Response::json(['status' => 'error', 'error_msg' => 'Failed, please contact supervisor']);
  }

  return \Response::json(['status' => 'ok']);
  }

}