laravel解决迁移文件一次删除创建字段报错的问题

<?php
 
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;
 
class CreateUserTable extends Migration{
  /**
   * 运行迁移
   *
   * @return void
   */
  public function up()
  {
    Schema::create('user', function (Blueprint $table) {
      if (Schema::hasColumn('topic')) {
        $table->dropColumn('topic');
      }
      $table->json('topic')->comment('主题');
    });
  }
 
  /**
   * 撤销迁移
   *
   * @return void
   */
  public function down()
  {
    //
  }
}