Dependency Inversion Principle 依赖倒置原则 dip

dip有两个原则
1.高层模块不应该依赖于底层模块，二者都应该依赖抽象
2.抽象不应该依赖细节，细节应该依赖于抽象

举一个例子

php后端项目，写一个列表数据的接口，带分页功能

输入的参数 有两个 page和per_page,

输出接口的字段有
total 数据的总数
per_page 每页数
current_page 当前页数
collection 具体的数据集合

以下是mysql的表结构

CREATE TABLE ba_admin_rule (
id int unsigned NOT NULL AUTO_INCREMENT COMMENT 'ID',
pid int unsigned NOT NULL DEFAULT '0' COMMENT '上级菜单',
type enum('menu_dir','menu','button') COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT 'menu' COMMENT '类型:menu_dir=菜单目录,menu=菜单项,button=页面按钮',
title varchar(50) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '' COMMENT '标题',
name varchar(50) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '' COMMENT '规则名称',
path varchar(100) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '' COMMENT '路由路径',
icon varchar(50) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '' COMMENT '图标',
menu_type enum('tab','link','iframe') COLLATE utf8mb4_unicode_ci DEFAULT NULL COMMENT '菜单类型:tab=选项卡,link=链接,iframe=Iframe',
url varchar(255) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '' COMMENT 'Url',
component varchar(100) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '' COMMENT '组件路径',
keepalive tinyint unsigned NOT NULL DEFAULT '0' COMMENT '缓存:0=关闭,1=开启',
extend enum('none','add_rules_only','add_menu_only') COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT 'none' COMMENT '扩展属性:none=无,add_rules_only=只添加为路由,add_menu_only=只添加为菜单',
remark varchar(255) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '' COMMENT '备注',
weigh int NOT NULL DEFAULT '0' COMMENT '权重',
status enum('0','1') COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '1' COMMENT '状态:0=禁用,1=启用',
update_time bigint unsigned DEFAULT NULL COMMENT '更新时间',
create_time bigint unsigned DEFAULT NULL COMMENT '创建时间',
PRIMARY KEY (id),
KEY pid (pid)
) ENGINE=InnoDB AUTO_INCREMENT=91 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci ROW_FORMAT=DYNAMIC COMMENT='菜单和权限规则表';

生成的pojo类

<?php

namespace App\Http\Pojo;

class AdminRulePojo
{
    private int $id;
    private int $pid = 0;
    private string $type = 'menu';
    private string $title = '';
    private string $name = '';
    private string $path = '';
    private string $icon = '';
    private ?string $menu_type = null;
    private string $url = '';
    private string $component = '';
    private int $keepalive = 0;
    private string $extend = 'none';
    private string $remark = '';

    private int $weigh = 0;
    private string $status = '1';
    private ?int $update_time = null;
    private ?int $create_time = null;

    public function getId(): int
    {
        return $this->id;
    }

    public function setId(int $id): void
    {
        $this->id = $id;
    }

    public function getPid(): int
    {
        return $this->pid;
    }

    public function setPid(int $pid): void
    {
        $this->pid = $pid;
    }

    public function getType(): string
    {
        return $this->type;
    }

    public function setType(string $type): void
    {
        $this->type = $type;
    }

    public function getTitle(): string
    {
        return $this->title;
    }

    public function setTitle(string $title): void
    {
        $this->title = $title;
    }

    public function getName(): string
    {
        return $this->name;
    }

    public function setName(string $name): void
    {
        $this->name = $name;
    }

    public function getPath(): string
    {
        return $this->path;
    }

    public function setPath(string $path): void
    {
        $this->path = $path;
    }

    public function getIcon(): string
    {
        return $this->icon;
    }

    public function setIcon(string $icon): void
    {
        $this->icon = $icon;
    }

    public function getMenuType(): ?string
    {
        return $this->menu_type;
    }

    public function setMenuType(?string $menu_type): void
    {
        $this->menu_type = $menu_type;
    }

    public function getUrl(): string
    {
        return $this->url;
    }

    public function setUrl(string $url): void
    {
        $this->url = $url;
    }

    public function getComponent(): string
    {
        return $this->component;
    }

    public function setComponent(string $component): void
    {
        $this->component = $component;
    }

    public function getKeepalive(): int
    {
        return $this->keepalive;
    }

    public function setKeepalive(int $keepalive): void
    {
        $this->keepalive = $keepalive;
    }

    public function getExtend(): string
    {
        return $this->extend;
    }

    public function setExtend(string $extend): void
    {
        $this->extend = $extend;
    }

    public function getRemark(): string
    {
        return $this->remark;
    }

    public function setRemark(string $remark): void
    {
        $this->remark = $remark;
    }

    public function getWeigh(): int
    {
        return $this->weigh;
    }

    public function setWeigh(int $weigh): void
    {
        $this->weigh = $weigh;
    }

    public function getStatus(): string
    {
        return $this->status;
    }

    public function setStatus(string $status): void
    {
        $this->status = $status;
    }

    public function getUpdateTime(): ?int
    {
        return $this->update_time;
    }

    public function setUpdateTime(?int $update_time): void
    {
        $this->update_time = $update_time;
    }

    public function getCreateTime(): ?int
    {
        return $this->create_time;
    }

    public function setCreateTime(?int $create_time): void
    {
        $this->create_time = $create_time;
    }
}

先声明接口的字段,这样可以快速跟前端对接。

{
  "code": 0,
  "message": "成功",
  "data": {
    "conllection": [
      {
        "id": 76,
        "pid": 0,
        "type": "menu",
        "title": "",
        "name": "",
        "path": "",
        "icon": "local-logo",
        "menu_type": null,
        "url": "",
        "component": "",
        "keepalive": 0,
        "extend": "none",
        "remark": "",
        "weigh": 0,
        "status": "1",
        "update_time": null,
        "create_time": null
      }
    ],
    "current_page": 1,
    "per_page": 1,
    "total": 1
  }
}

这个是定义好的分页数据返回类,

<?php

namespace App\Http\Pagination;

use App\Http\Pojo\AdminRulePojo;

class AdminRulePagination
{
    // use Pagination;

    protected int $current_page;

    protected int $per_page;

    protected int $total;
    protected array $conllection = [];

    public function getConllection(): array
    {
        return $this->conllection;
    }

    public function addConllection(AdminRulePojo $adminRulePojo): void
    {
        $this->conllection[] = $adminRulePojo;
    }

    public function getCurrentPage(): int
    {
        return $this->current_page;
    }

    public function setCurrentPage(int $current_page): void
    {
        $this->current_page = $current_page;
    }

    public function getPerPage(): int
    {
        return $this->per_page;
    }

    public function setPerPage(int $per_page): void
    {
        $this->per_page = $per_page;
    }

    public function getTotal(): int
    {
        return $this->total;
    }

    public function setTotal(int $total): void
    {
        $this->total = $total;
    }
}

因为php不支持泛型。所以用以下的方法来实现同一对象集合

 protected array $conllection = [];

    public function getConllection(): array
    {
        return $this->conllection;
    }

    public function addConllection(AdminRulePojo $adminRulePojo): void
    {
        $this->conllection[] = $adminRulePojo;
    }

然后定义list返回数据的接口,定义好接收的参数和返回的类型.

<?php

namespace App\Http\Service;

use App\Http\Pagination\AdminRulePagination;

interface IAdminRuleService
{
    public function list(int $per_page) :AdminRulePagination;
}

接口实现类

<?php

namespace App\Http\Service\impl;

use App\Http\Pagination\AdminRulePagination;
use App\Http\Pojo\AdminRulePojo;
use App\Http\Service\IAdminRuleService;
use App\Models\AdminRuleModel;

class AdminRuleService implements IAdminRuleService
{
    private AdminRuleModel $adminRuleModel;

    private AdminRulePagination $adminRulePagination;

    public function __construct(AdminRuleModel $adminRuleModel,AdminRulePagination $adminRulePagination)
    {
        $this->adminRuleModel=$adminRuleModel;
        $this->adminRulePagination=$adminRulePagination;
    }

    public function list(int $per_page) :AdminRulePagination
    {
        $res = $this->adminRuleModel::where('status', 1)->paginate($per_page)->toArray();

        if (!empty($res['data'])) {
            foreach ($res['data'] as $item) {
                $AdminRulePojo = new AdminRulePojo();
                $AdminRulePojo->setComponent($item['component']);
                $AdminRulePojo->setId($item['id']);
                $AdminRulePojo->setIcon($item['icon']);
                $this->adminRulePagination->addConllection($AdminRulePojo);
            }
        }

        $this->adminRulePagination->setCurrentPage($res['current_page']);
        $this->adminRulePagination->setTotal($res['total']);
        $this->adminRulePagination->setPerPage($res['per_page']);

        return $this->adminRulePagination;
    }
}

使用laravel的服务容器，控制反转，来绑定接口和实现类。

$this->app->bind(IAdminRuleService::class, AdminRuleService::class);

定义好接口

之后的实现类。可以换成原生sql查询的。其他数据库查询的。

比如mangodb获取数据的。

<?php

namespace App\Http\Service\impl;

use App\Http\Pagination\AdminRulePagination;
use App\Http\Pojo\AdminRulePojo;
use App\Http\Service\IAdminRuleService;
use App\Models\AdminRuleModel;
use Illuminate\Support\Facades\DB;

class MangoDbAdminRuleService implements IAdminRuleService
{
    private AdminRulePagination $adminRulePagination;

    public function __construct(AdminRulePagination $adminRulePagination)
    {
        $this->adminRulePagination=$adminRulePagination;
    }

    public function list(int $per_page) :AdminRulePagination
    {

    }
}

在服务容器那里改一下绑定就可以了。

 $this->app->bind(IAdminRuleService::class, MangoDbAdminRuleService::class);

这个是控制器,声明接口变量IAdminRuleService

<?php

namespace App\Http\ServiceController;

use App\Http\Service\IAdminRuleService;

class AdminRule
{
    use ServiceController;

    use Response;

    private IAdminRuleService $adminRuleService;

    public function __construct(IAdminRuleService $adminRuleService)
    {
        $this->adminRuleService = $adminRuleService;
    }

    public function list(int $per_page): array
    {
        $obj = $this->adminRuleService->list($per_page);

        $data = $this->objectToArray($obj);

        $this->setData($data);

        return $this->Success();
    }
}

以上就是这个依赖倒置的例子。

这个php的api接口查询数据的例子。可以随时换框架，随时换数据库操作类。使用orm或者sql查询的都行，也可以换数据库类型。

控制器作为高层模块，不依赖低层service层模块。两者通过接口和定义好的数据类AdminRulePagination来交换数据。

符合了依赖倒置的两大原则

1.高层模块不应该依赖于底层模块，二者都应该依赖抽象

2.抽象不应该依赖细节，细节应该依赖于抽象

抽象不依赖细节，按这个例子的情况就是，控制器层依赖IAdminRuleService接口，而不是依赖具体的实现类。

这个例子有点复杂。说了一些泛型的东西。但是实现这个过程中，会遇到php的缺点和不足。如果以上的例子用java实现。那就会容易一些。