yii2自动更新时间，根据条件设定指定值，接受多选框的值

<?php
namespace backend\models;
use Yii;
use \yii\db\ActiveRecord;
class Newdocument extends ActiveRecord
{
    public function beforeSave($insert){
        if(parent::beforeSave($insert)){
            if($this->isNewRecord){//判断是更新还是插入
                $this->connect = implode(',', $this->connect);
                $this->create_time = time();
            }else{
                $this->update_time = time();
                $this->connect = implode(',', $this->connect);
            }
           return true;
        }else{
            return false;
        }
    }
    /**
     * @inheritdoc
     */
    public static function tableName()
    {
        return 'document';
    }
    /**
     * @inheritdoc
     */
    public function rules()
    {
        return [
            [[  'create_time','update_time'], 'integer'],
            ['connect','tostring'],
        ];
    }
    public function tostring(){//可通过方法单独控制某个字段，也可以直接通过beforesave方法控制
            //if($this->isNewRecord){//判断是更新还是插入
                //$this->connect = implode(',', $this->connect);
            //}else{
               // $this->connect = implode(',', $this->connect);
            //}
    }