Laravel5.2之模型关联预加载

说明：本文主要说明Laravel Eloquent的延迟预加载(Eager Loading)，使用延迟预加载来减少MySQL查询次数。同时，会将开发过程中的一些截图和代码黏上去，提高阅读效率。
备注：现在有4张表：商家表merchants、商家电话表phones、商家拥有的店铺shops表和店铺里的商品表products。并且关系是：

[
'merchants_phones' => 'one-to-one',
'merchants_shops'  => 'one-to-many',
'shops_products'   => 'one-to-many',
]

现在要求做出一个页面以列表形式显示每个店铺，每个店铺块包含店铺信息如标题、包含店铺商家信息如姓名和电话、包含拥有的商品信息如介绍和价格。看看有没有预加载会有什么不同。

开发环境：Laravel5.1+MAMP+PHP7+MySQL5.5

先写个店铺列表页

1.先装上开发插件三件套

(具体可参考：Laravel5.2之Seeder填充数据小技巧)
不管咋样，先装上开发插件三件套：

composer require barryvdh/laravel-debugbar --dev
composer require barryvdh/laravel-ide-helper --dev
composer require mpociot/laravel-test-factory-helper --dev

//config/app.php
/** *Develop Plugin */
Barryvdh\Debugbar\ServiceProvider::class,
Mpociot\LaravelTestFactoryHelper\TestFactoryHelperServiceProvider::class,
Barryvdh\LaravelIdeHelper\IdeHelperServiceProvider::class,

2.写上表字段、表关联和测试数据填充器Seeder

依次输入指令：

php artisan make:model Merchant -m
php artisan make:model Phone -m
php artisan make:model Shop -m
php artisan make:model Product -m

写上表字段和表关联：

class CreateMerchantsTable extends Migration
{
/**
* Run the migrations.
*
* @return void
*/
public function up()
{
Schema::create('merchants', function (Blueprint $table) {
$table->increments('id');
$table->string('username')->unique();
$table->string('email')->unique();
$table->string('first_name');
$table->string('last_name');
$table->timestamps();
});
}

/**
* Reverse the migrations.
*
* @return void
*/
public function down()
{
Schema::drop('merchants');
}
}

class CreatePhonesTable extends Migration
{
/**
* Run the migrations.
*
* @return void
*/
public function up()
{
Schema::create('phones', function (Blueprint $table) {
$table->increments('id');
$table->integer('number')->unsigned();
$table->integer('merchant_id')->unsigned();
$table->timestamps();
$table->foreign('merchant_id')
->references('id')
->on('merchants')
->onUpdate('cascade')
->onDelete('cascade');
});
}

/**
* Reverse the migrations.
*
* @return void
*/
public function down()
{
Schema::table('phones', function($table){
$table->dropForeign('merchant_id'); // Drop foreign key 'user_id' from 'posts' table
});
Schema::drop('phones');
}
}

class CreateShopsTable extends Migration
{
/**
* Run the migrations.
*
* @return void
*/
public function up()
{
Schema::create('shops', function (Blueprint $table) {
$table->increments('id');
$table->string('name');
$table->string('slug')->unique();
$table->string('site');
$table->integer('merchant_id')->unsigned();
$table->timestamps();
$table->foreign('merchant_id')
->references('id')
->on('merchants')
->onUpdate('cascade')
->onDelete('cascade');
});
}

/**
* Reverse the migrations.
*
* @return void
*/
public function down()
{
Schema::table('shops', function($table){
$table->dropForeign('merchant_id'); // Drop foreign key 'user_id' from 'posts' table
});
Schema::drop('shops');
}
}

class CreateProductsTable extends Migration
{
/**
* Run the migrations.
*
* @return void
*/
public function up()
{
Schema::create('products', function (Blueprint $table) {
$table->increments('id');
$table->string('name');
$table->text('short_desc');
$table->text('long_desc');
$table->double('price');
$table->integer('shop_id')->unsigned();
$table->timestamps();
$table->foreign('shop_id')
->references('id')
->on('shops')
->onUpdate('cascade')
->onDelete('cascade');
});
}

/**
* Reverse the migrations.
*
* @return void
*/
public function down()
{
Schema::table('products', function($table){
$table->dropForeign('shop_id'); // Drop foreign key 'user_id' from 'posts' table
});
Schema::drop('products');
}
}

/**
* App\Merchant
*
* @property integer $id
* @property string $username
* @property string $email
* @property string $first_name
* @property string $last_name
* @property \Carbon\Carbon $created_at
* @property \Carbon\Carbon $updated_at
* @property-read \App\Phone $phone
* @property-read \Illuminate\Database\Eloquent\Collection|\App\Shop[] $shops
* @method static \Illuminate\Database\Query\Builder|\App\Merchant whereId($value)
* @method static \Illuminate\Database\Query\Builder|\App\Merchant whereUsername($value)
* @method static \Illuminate\Database\Query\Builder|\App\Merchant whereEmail($value)
* @method static \Illuminate\Database\Query\Builder|\App\Merchant whereFirstName($value)
* @method static \Illuminate\Database\Query\Builder|\App\Merchant whereLastName($value)
* @method static \Illuminate\Database\Query\Builder|\App\Merchant whereCreatedAt($value)
* @method static \Illuminate\Database\Query\Builder|\App\Merchant whereUpdatedAt($value)
* @mixin \Eloquent
*/
class Merchant extends Model
{
/**
* @return \Illuminate\Database\Eloquent\Relations\HasOne
*/
public function phone()
{
return $this->hasOne(Phone::class, 'merchant_id');
}

/**
* @return \Illuminate\Database\Eloquent\Relations\HasMany
*/
public function shops()
{
return $this->hasMany(Shop::class, 'merchant_id');
}
}

/**
* App\Phone
*
* @property integer $id
* @property integer $number
* @property integer $merchant_id
* @property \Carbon\Carbon $created_at
* @property \Carbon\Carbon $updated_at
* @property-read \App\Merchant $merchant
* @method static \Illuminate\Database\Query\Builder|\App\Phone whereId($value)
* @method static \Illuminate\Database\Query\Builder|\App\Phone whereNumber($value)
* @method static \Illuminate\Database\Query\Builder|\App\Phone whereMerchantId($value)
* @method static \Illuminate\Database\Query\Builder|\App\Phone whereCreatedAt($value)
* @method static \Illuminate\Database\Query\Builder|\App\Phone whereUpdatedAt($value)
* @mixin \Eloquent
*/
class Phone extends Model
{
/**
* @return \Illuminate\Database\Eloquent\Relations\BelongsTo
*/
public function merchant()
{
return $this->belongsTo(Merchant::class, 'merchant_id');
}
}

/**
* App\Product
*
* @property integer $id
* @property string $name
* @property string $short_desc
* @property string $long_desc
* @property float $price
* @property integer $shop_id
* @property \Carbon\Carbon $created_at
* @property \Carbon\Carbon $updated_at
* @property-read \Illuminate\Database\Eloquent\Collection|\App\Shop[] $shop
* @method static \Illuminate\Database\Query\Builder|\App\Product whereId($value)
* @method static \Illuminate\Database\Query\Builder|\App\Product whereName($value)
* @method static \Illuminate\Database\Query\Builder|\App\Product whereShortDesc($value)
* @method static \Illuminate\Database\Query\Builder|\App\Product whereLongDesc($value)
* @method static \Illuminate\Database\Query\Builder|\App\Product wherePrice($value)
* @method static \Illuminate\Database\Query\Builder|\App\Product whereShopId($value)
* @method static \Illuminate\Database\Query\Builder|\App\Product whereCreatedAt($value)
* @method static \Illuminate\Database\Query\Builder|\App\Product whereUpdatedAt($value)
* @mixin \Eloquent
*/
class Product extends Model
{
/**
* @return \Illuminate\Database\Eloquent\Relations\BelongsTo
*/
public function shop()
{
return $this->belongsTo(Shop::class, 'shop_id');
}
}

/**
* App\Shop
*
* @property integer $id
* @property string $name
* @property string $slug
* @property string $site
* @property integer $merchant_id
* @property \Carbon\Carbon $created_at
* @property \Carbon\Carbon $updated_at
* @property-read \Illuminate\Database\Eloquent\Collection|\App\Merchant[] $merchant
* @property-read \Illuminate\Database\Eloquent\Collection|\App\Product[] $products
* @method static \Illuminate\Database\Query\Builder|\App\Shop whereId($value)
* @method static \Illuminate\Database\Query\Builder|\App\Shop whereName($value)
* @method static \Illuminate\Database\Query\Builder|\App\Shop whereSlug($value)
* @method static \Illuminate\Database\Query\Builder|\App\Shop whereSite($value)
* @method static \Illuminate\Database\Query\Builder|\App\Shop whereMerchantId($value)
* @method static \Illuminate\Database\Query\Builder|\App\Shop whereCreatedAt($value)
* @method static \Illuminate\Database\Query\Builder|\App\Shop whereUpdatedAt($value)
* @mixin \Eloquent
*/
class Shop extends Model
{
/**
* @return \Illuminate\Database\Eloquent\Relations\BelongsTo
*/
public function merchant()
{
return $this->belongsTo(Merchant::class, 'merchant_id');
}

/**
* @return \Illuminate\Database\Eloquent\Relations\HasMany
*/
public function products()
{
return $this->hasMany(Product::class, 'shop_id');
}
}

别忘了利用下开发三件套输入指令：

php artisan ide-helper:generate
php artisan ide-helper:models
php artisan test-factory-helper:generate

表的关系如图：



然后写Seeder，可以参考Laravel5.2之Seeder填充数据小技巧:

php artisan make:seeder MerchantTableSeeder
php artisan make:seeder PhoneTableSeeder
php artisan make:seeder ShopTableSeeder
php artisan make:seeder ProductTableSeeder
class MerchantTableSeeder extends Seeder
{
/** * Run the database seeds. * * @return void */
public function run()
{
$faker = Faker\Factory::create();
$datas = [];
foreach (range(1, 20) as $key => $value) {
$datas[] = [
'username'   =>  $faker->userName ,
'email'      =>  $faker->safeEmail ,
'first_name' =>  $faker->firstName ,
'last_name'  =>  $faker->lastName ,
'created_at' => \Carbon\Carbon::now()->toDateTimeString(),
'updated_at' => \Carbon\Carbon::now()->toDateTimeString()
];
}

DB::table('merchants')->insert($datas);
}
}

class PhoneTableSeeder extends Seeder
{
/** * Run the database seeds. * * @return void */
public function run()
{
$faker        = Faker\Factory::create();
$merchant_ids = \App\Merchant::lists('id')->toArray();
$datas        = [];
foreach (range(1, 20) as $key => $value) {
$datas[]  = [
'number'      => $faker->randomNumber() ,
'merchant_id' => $faker->randomElement($merchant_ids) ,
'created_at'  => \Carbon\Carbon::now()->toDateTimeString(),
'updated_at'  => \Carbon\Carbon::now()->toDateTimeString()
];
}

DB::table('phones')->insert($datas);
}
}

class ShopTableSeeder extends Seeder
{
/** * Run the database seeds. * * @return void */
public function run()
{
$faker        = Faker\Factory::create();
$merchant_ids = \App\Merchant::lists('id')->toArray();
$datas        = [];
foreach (range(1, 40) as $key => $value) {
$datas[]  = [
'name'         =>  $faker->name ,
'slug'         =>  $faker->slug ,
'site'         =>  $faker->word ,
'merchant_id'  =>  $faker->randomElement($merchant_ids) ,
'created_at'   => \Carbon\Carbon::now()->toDateTimeString(),
'updated_at'   => \Carbon\Carbon::now()->toDateTimeString()
];
}

DB::table('shops')->insert($datas);
}
}

class ProductTableSeeder extends Seeder
{
/** * Run the database seeds. * * @return void */
public function run()
{
$faker    = Faker\Factory::create();
$shop_ids = \App\Shop::lists('id')->toArray();
$datas    = [];
foreach (range(1, 30) as $key => $value) {
$datas[] = [
'name'              =>  $faker->name ,
'short_desc'        =>  $faker->text ,
'long_desc'         =>  $faker->text ,
'price'             =>  $faker->randomFloat() ,
'shop_id'           =>  $faker->randomElement($shop_ids) ,
'created_at'        =>  \Carbon\Carbon::now()->toDateTimeString() ,
'updated_at'        =>  \Carbon\Carbon::now()->toDateTimeString()
];
}

DB::table('products')->insert($datas);
}
}

php artisan db:seed

3.写个简单View视图

(1)用Repository Pattern来组织代码

//app/Repository
namespace App\Repository;
interface ShopRepositoryInterface
{
public function all();
}
//app/Repository/Eloquent
namespace App\Repository\Eloquent;

use App\Repository\ShopRepositoryInterface;
use App\Shop;

class ShopRepository implements ShopRepositoryInterface
{
/**
* @var Shop
*/
public $shop;
public function __construct(Shop $shop)
{
$this->shop = $shop;
}

public function all()
{
// TODO: Implement all() method.
$shops = $this->shop->all();
return $shops;
}
}
//app/provider/ShopRepositoryServiceProvider
//php artisan make:provider ShopRepositoryServiceProvider
/**
* Register the application services.
*
* @return void
*/
public function register()
{
$this->app->bind(ShopRepositoryInterface::class, ShopRepository::class);
}

//app/Http/Controllers/ShopController.php
class ShopController extends Controller
{
/**
* @var ShopRepositoryInterface
*/
public $shop;

/**
* ShopController constructor.
* @param ShopRepositoryInterface $shopRepositoryInterface
*/
public function __construct(ShopRepositoryInterface $shopRepositoryInterface)
{
$this->shop = $shopRepositoryInterface;
}

public function all()
{
$shops = $this->shop->all();
return view('shop.index', compact('shops'));
}
}

//视图
//resources/views/shop/layout.blade.php
<html lang="en">
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<!-- 上述3个meta标签*必须*放在最前面，任何其他内容都*必须*跟随其后！ -->
<title>Bootstrap Template</title>
<!-- 新 Bootstrap 核心 CSS 文件 -->
<link rel="stylesheet" href="//cdn.bootcss.com/bootstrap/3.3.5/css/bootstrap.min.css">
<style>
html,body{
width: 100%;
height: 100%;
}
*{
margin: 0;
border: 0;
}
</style>
</head>
<body>
<div class="container">
<div class="row">
<div class="col-xs-12 col-md-12">

@yield('content')

</div>
</div>
</div>

<!-- jQuery文件。务必在bootstrap.min.js 之前引入 -->
<script src="//cdn.bootcss.com/jquery/1.11.3/jquery.min.js"></script>
<!-- 最新的 Bootstrap 核心 JavaScript 文件 -->
<script src="//cdn.bootcss.com/bootstrap/3.3.5/js/bootstrap.min.js"></script>
<script>

</script>
</body>
</html>

//resources/views/shop/index.blade.php
@extends('shop.layout')

@section('content')
<ul class="list-group">
@foreach($shops as $shop)
<li class="list-group-item" style="margin-top: 10px">
<h1><strong style="color: darkred">Store:</strong>{{$shop->name}}</h1>
<span><strong style="color: orangered">Member:</strong>{{$shop->merchant->first_name.' '.$shop->merchant->last_name}}</span>
{{--这里数组取电话号码--}}
<span><strong style="color: orangered">Phone:</strong>{{$shop->merchant->phone['number']}}</span>
<ul class="list-group">
@foreach($shop->products as $product)
<li class="list-group-item">
<h3><strong style="color: red">Name:</strong>{{$product->name}}</h3>
<h4><strong style="color: red">Desc:</strong>{{$product->short_desc}}</h4>
<h4><strong style="color: red">Price:</strong>{{$product->price}}</h4>

{{--                            {!! Debugbar::info('products:'.$product->id) !!}--}}
</li>
@endforeach
</ul>
</li>
@endforeach
</ul>

@endsection

//路由
Route::get('/eagerload', 'ShopController@all');

(2)Debugbar查看程序执行数据

可以看到，执行了121次query，耗时38.89ms，效率很低，仔细观察每一个statement就发现这是先扫描shops表，再根据shops中每一个merchant_id去查找merchants表，查找products表也是这样，又有很多次query，这是N+1查找问题。

预加载查询

(1)嵌套预加载

Eloquent在通过属性访问关联数据时是

延迟加载

的，就是只有该关联数据只有在通过属性访问它时才会被加载。在查找上层模型时可以通过预加载关联数据，避免N+1问题。

而且，使用预加载超级简单。

只需修改一行：

//app/Repository/Eloquent/ShopRepository
public function all()
{
// TODO: Implement all() method.
// $shops = $this->shop->all();
//通过`点`语法嵌套预加载，多种关联就写对应的关联方法
//Shop这个Model里关联方法是Merchant()和Products()，Merchant Model里关联方法是Phone()
$shops = $this->shop->with(['merchant.phone', 'products'])->get();
return $shops;
}

不需要修改其他代码，再看Debugbar里的查询：

It is working!!!

发现：只有4个query，耗时3.58ms，效率提高很多。把原来的N+1这种query改造成了

where..in..

这种query，效率提高不少。可以用EXPLAIN来查看SQL语句的执行计划。

(2)预加载条件限制

还可以对预加载进行条件限制，如对products进行预先排序，代码也很好修改，只需：

//app/Repository/Eloquent/ShopRepository
public function all()
{
// TODO: Implement all() method.
// $shops = $this->shop->all();
// $shops = $this->shop->with(['merchant.phone', 'products'])->get();
$shops = $this->shop->with(['members.phone', 'products'=>function($query){
// $query->orderBy('price', 'desc');
$query->orderBy('price', 'asc');
}])->get();
return $shops;
}

通过加个限制条件，就等于在预加载products时SQL语句上加个排序。截图就不截取了。

昨天看到有个问题是问Laravel值不值得花时间玩一玩，个人自学Laravel有几个月了，玩PHP也11个月，开始发现PHP的代码非常面条式，但后来了解到Laravel和Composer后，发现PHP原来很强大的，个人建议Laravel是值得花时间玩一玩的，也推荐一本书《Modern PHP》。其实写代码需要些很多东西的，而不仅仅面条式业务逻辑，比如用PHPUnit写单元测试和集成测试，各种设计模式，SOLID原则，依赖注入和控制反转的容器等等，这些东西个人都是玩Laravel后才了解并学习了一些，就个人而言，玩Laravel后学到了很多代码技巧，感觉到编程是一项技术活，不是体力活。

总结：关联模型预加载的确是个有意思的功能，效率提高不少。最近都在瞎研究，遇到好玩的东西再分享出来吧，到时见。