這篇文章將為大家詳細講解有關Laravel之模型關聯預加載的示例分析，小編覺得挺實用的，因此分享給大家做個參考，希望大家閱讀完這篇文章后可以有所收獲。
Laravel學習筆記之模型關聯預加載
說明：本文主要說明Laravel Eloquent的延遲預加載(Eager Loading)，使用延遲預加載來減少MySQL查詢次數。同時，作者會將開發過程中的一些截圖和代碼黏上去，提高閱讀效率。
備注：現在有4張表：商家表merchants、商家電話表phones、商家擁有的店鋪shops表和店鋪里的商品表products。并且關系是：
[ 'merchants_phones' => 'one-to-one', 'merchants_shops' => 'one-to-many', 'shops_products' => 'one-to-many', ]
現在要求做出一個頁面以列表形式顯示每個店鋪，每個店鋪塊包含店鋪信息如標題、包含店鋪商家信息如姓名和電話、包含擁有的商品信息如介紹和價格?？纯从袥]有預加載會有什么不同。
開發環境：Laravel5.1+MAMP+PHP7+MySQL5.5
1.先裝上開發插件三件套(具體可參考：Laravel學習筆記之Seeder填充數據小技巧)
不管咋樣，先裝上開發插件三件套：
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.寫上表字段、表關聯和測試數據填充器Seeder
依次輸入指令：
php artisan make:model Merchant -m php artisan make:model Phone -m php artisan make:model Shop -m php artisan make:model Product -m
寫上表字段和表關聯：
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');
}
}別忘了利用下開發三件套輸入指令：
php artisan ide-helper:generate php artisan ide-helper:models php artisan test-factory-helper:generate
表的關系如圖：
然后寫Seeder，可以參考Laravel學習筆記之Seeder填充數據小技巧:
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:seed3.寫個簡單View視圖(1)用Repository Pattern來組織代碼
//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 = $this->shop->all();
return view('shop.index', compact('shops'));
}
}
//視圖
//resources/views/shop/layout.blade.php
<html lang="en">
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<!-- 上述3個meta標簽*必須*放在最前面，任何其他內容都*必須*跟隨其后！ -->
<title>Bootstrap Template</title>
<!-- 新 Bootstrap 核心 CSS 文件 -->
<link rel="stylesheet" href="//cdn.bootcss.com/bootstrap/3.3.5/css/bootstrap.min.css">
<style>
html,body{
width: 100%;
height: 100%;
}
*{
margin: 0;
border: 0;
}
</style>
</head>
<body>
<p class="container">
<p class="row">
<p class="col-xs-12 col-md-12">
@yield('content')
</p>
</p>
</p>
<!-- jQuery文件。務必在bootstrap.min.js 之前引入 -->
<script src="//cdn.bootcss.com/jquery/1.11.3/jquery.min.js"></script>
<!-- 最新的 Bootstrap 核心 JavaScript 文件 -->
<script src="//cdn.bootcss.com/bootstrap/3.3.5/js/bootstrap.min.js"></script>
<script>
</script>
</body>
</html>
//resources/views/shop/index.blade.php
@extends('shop.layout')
@section('content')
<ul class="list-group">
@foreach($shops as $shop)
<li class="list-group-item" style="margin-top: 10px">
<h2><strong style="color: darkred">Store:</strong>{{$shop->name}}</h2>
<span><strong style="color: orangered">Member:</strong>{{$shop->merchant->first_name.' '.$shop->merchant->last_name}}</span>
{{--這里數組取電話號碼--}}
<span><strong style="color: orangered">Phone:</strong>{{$shop->merchant->phone['number']}}</span>
<ul class="list-group">
@foreach($shop->products as $product)
<li class="list-group-item">
<h4><strong style="color: red">Name:</strong>{{$product->name}}</h4>
<h5><strong style="color: red">Desc:</strong>{{$product->short_desc}}</h5>
<h5><strong style="color: red">Price:</strong>{{$product->price}}</h5>
{{-- {!! Debugbar::info('products:'.$product->id) !!}--}}
</li>
@endforeach
</ul>
</li>
@endforeach
</ul>
@endsection
//路由
Route::get('/eagerload', 'ShopController@all');(2)Debugbar查看程序執行數據
可以看到，執行了121次query，耗時38.89ms，效率很低，仔細觀察每一個statement就發現這是先掃描shops表，再根據shops中每一個merchant_id去查找merchants表，查找products表也是這樣，又有很多次query，這是N+1查找問題。
(1)嵌套預加載
Eloquent在通過屬性訪問關聯數據時是延遲加載的，就是只有該關聯數據只有在通過屬性訪問它時才會被加載。在查找上層模型時可以通過預加載關聯數據，避免N+1問題。而且，使用預加載超級簡單。
只需修改一行：
//app/Repository/Eloquent/ShopRepository
public function all()
{
// TODO: Implement all() method.
// $shops = $this->shop->all();
//通過`點`語法嵌套預加載，多種關聯就寫對應的關聯方法
//Shop這個Model里關聯方法是Merchant()和Products()，Merchant Model里關聯方法是Phone()
$shops = $this->shop->with(['merchant.phone', 'products'])->get();
return $shops;
}不需要修改其他代碼，再看Debugbar里的查詢：
It is working!!!
發現：只有4個query，耗時3.58ms，效率提高很多。把原來的N+1這種query改造成了where..in..這種query，效率提高不少?？梢杂肊XPLAIN來查看SQL語句的執行計劃。
(2)預加載條件限制
還可以對預加載進行條件限制，如對products進行預先排序，代碼也很好修改，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;
}通過加個限制條件，就等于在預加載products時SQL語句上加個排序。
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