01.模型和ORM

1.ORM是什么？

 ORM(Object Relation Mapping)对象映射关系。ORM一种将数据表抽象成对象的编程思想。简单点，可以当成一个数据表对应一个对象，对数据的操作不再看成是对数据表的操作，表与表之间的关系也不再是外键和内键的关系，而是对象与对象的作用关系。
TP5.0的ORM主要应用在模型中对数据库的操作中。

2. 关联模型

2.1 相对关联模型(内嵌关联模型)

1，主模型

<?php
namespace app\api\model;
use think\Model;
class Banner extends Model
{
    public function bannerItem()
    {
        ///多对多Banner模型关联BannerItem模型 
        return $this->hasMany("BannerItem","banner_id","id");
    }
}

2, 关联模型

<?php
namespace app\api\model;
use think\Model;
class BannerItem extends Model
{
    public function Image() {
        //相对关联
        return $this->BelongsTo("Image","img_id","id");
    }
}

3，Images模型

<?php
namespace app\api\model;
use think\Model;
class Image extends Model
{
    
}

4，调用

<?php
namespace app\api\controller\v1;
use think\Controller;
use app\api\model\Banner as BannerModel;
class Banner extends Controller
{
    public function getBanner($id)
    {
        //内嵌关联模型调用
        $result = BannerModel::get($id,['BannerItem','BannerItem.Image' ]);
        return json($result);
    }
}

5,输出

{
    "id": 1,
    "name": "首页置顶",
    "description": "首页轮播图",
    "delete_time": null,
    "update_time": "1970-01-01 08:00:00",
    "banner_item": [
        {
            "id": 1,
            "img_id": 65,
            "key_word": "6",
            "type": 1,
            "delete_time": null,
            "banner_id": 1,
            "update_time": "1970-01-01 08:00:00",
            "image": {
                "id": 65,
                "url": "/banner-4a.png",
                "from": 1,
                "delete_time": null,
                "update_time": "1970-01-01 08:00:00"
            }
        },
        {
            "id": 2,
            "img_id": 2,
            "key_word": "25",
            "type": 1,
            "delete_time": null,
            "banner_id": 1,
            "update_time": "1970-01-01 08:00:00",
            "image": {
                "id": 2,
                "url": "/banner-2a.png",
                "from": 1,
                "delete_time": null,
                "update_time": "1970-01-01 08:00:00"
            }
        },
        {
            "id": 3,
            "img_id": 3,
            "key_word": "11",
            "type": 1,
            "delete_time": null,
            "banner_id": 1,
            "update_time": "1970-01-01 08:00:00",
            "image": {
                "id": 3,
                "url": "/banner-3a.png",
                "from": 1,
                "delete_time": null,
                "update_time": "1970-01-01 08:00:00"
            }
        },
        {
            "id": 5,
            "img_id": 1,
            "key_word": "10",
            "type": 1,
            "delete_time": null,
            "banner_id": 1,
            "update_time": "1970-01-01 08:00:00",
            "image": {
                "id": 1,
                "url": "/banner-1a.png",
                "from": 1,
                "delete_time": null,
                "update_time": "1970-01-01 08:00:00"
            }
        }
    ]
}