Laravel5.4框架中解决特殊字段太长导致migrations报错的方法

 [Illuminate\Database\QueryException]
 SQLSTATE[42000]: Syntax error or access violation: 1071 Specified key was too long; max key length is 767 bytes (SQL: alter table `users` add unique `use
 rs_email_unique`(`email`))
 
 [PDOException]
 SQLSTATE[42000]: Syntax error or access violation: 1071 Specified key was too long; max key length is 767 bytes

<?php
namespace App\Providers;
use Illuminate\Support\ServiceProvider;
//添加的代码
use Illuminate\Support\Facades\Schema;
 
class AppServiceProvider extends ServiceProvider
{
 /**
  * Bootstrap any application services.
  *
  * @return void
  */
 public function boot()
 {
  //添加的代码
  Schema::defaultStringLength(191);
 }
 
 /**
  * Register any application services.
  *
  * @return void
  */
 public function register()
 {
  //
 }
}