csapi/application/index/model/BuyCarModel.php

<?php
namespace app\index\model;
class BuyCarModel extends BaseModel
{
    protected $table='buy_car';
    protected $connection = 'db_mall';

    /**
     * 购物车表联合产品表
     * @param $condition
     * @param $order
     * @return false|\PDOStatement|string|\think\Collection
     */
    public function getCarAndProductInfo($condition,$order='pro.category_id asc'){

        $list = $this->join('product pro','pro.product_id = buy_car.product_id','LEFT')
            ->field("buy_car.num as num,buy_car.id as buy_car_id,pro.*")
            ->where($condition)->order($order)->select();

        return $list;
    }
}