Laravel 4 Eager Loading n + 1期

Question

我有急切的加載/ n + 1問題，研究和閱讀和觀看關於這個問題的教程整天排除故障，但還沒有解決它。我已經建立了模型的關係，但是當我用輔助函數傳遞數據時，我得到了這個n + 1問題。 我想從url site.com/Artist/songs獲取藝術家名稱，並獲取所有歌曲並顯示這樣的網址。

site.com/$Artist/songs/$id

我的藝術家/ index.blade.php視圖看起來像這樣http://i61.tinypic.com/2nqzatk.jpg 我不知道我在這裏失蹤。

在此先感謝！

我的表

歌曲 ID，標題，正文，蛞蝓，命中，artist_id，created_at，的updated_at

藝術家 ID，姓名，身體，created_at，的updated_at

routes.php文件

Event::listen('illuminate.query', function($query) 
{ 
    var_dump($query); 
}); 
... 
Route::get('{artist}/songs', 'ArtistsController@index'); 
Route::get('{artist}/songs/{id}', ['as' => 'artist.songs.show', 'uses' => 'ArtistsController@show']); 

型號：Song.php

class Song extends Eloquent { 
    protected $guarded = ['id']; 

    /** 
    * Setting up relationship for the artist model for easier usage 
    * 
    */ 
    public function artist() 
    { 
     return $this->belongsTo('Artist'); 
    } 

    // Override find method 
    public static function find($id, $name = null) 
    { 
     $song = static::with('artist')->find($id); 

     // If the song is found 
     if ($song) 
     { 
      // If the song doesn't belong to that artist, throw an exception which will redirect to home, defined in global.php 
      if ($name and $song->artist->name !== $name) 
      { 
       throw new Illuminate\Database\Eloquent\ModelNotFoundException; 
      } 

      return $song; 
     } 
     // If the song is not found, throw an exception which will redirect to home, defined in global.php 
     else 
     { 
      throw new Illuminate\Database\Eloquent\ModelNotFoundException; 
     } 

    } 

    // Get songs from artist 
    public static function byArtist($name) 
    { 
     return Artist::byName($name)->songs; 
    } 

} 

模型Artist.php

class Artist extends Eloquent { 
    protected $fillable = []; 

    /** 
    * Setting up relationship with the song model for easier usage 
    * $artist->songs; 
    */ 
    public function songs() 
    { 
     return $this->hasMany('Song'); 
    } 

    // Get artist by name 
    public static function byName($name) 
    { 
     return static::whereName($name)->first(); 
    } 

} 

控制器：ArtistsController.php

class ArtistsController extends BaseController { 

    // Set default layout for this controller 
    protected $layout = 'layouts.master'; 

    /** 
    * Display a listing of the resource. 
    * GET /artists 
    * 
    * @return Response 
    */ 
    public function index($name) 
    { 
     $this->data['songs'] = Song::byArtist($name); 

     $this->layout->content = View::make('artists.index', $this->data); 
    } 

helpers.php

function link_to_artist_song(Song $song) 
{ 
    return link_to_route('artist.songs.show', $song->title, [$song->artist->name, $song->id]); 
} 

爲藝術家 藝術家/ index.blade索引圖。 php http://i61.tinypic.com/2nqzatk.jpg

@extends('layouts.master') 

@section('content') 

    @if(isset($songs)) 
     <h1>All Songs</h1> 

     <ul class="list-group"> 
     @foreach($songs as $song) 
      <li class="list-group-item">{{ link_to_artist_song($song) }}</li> 
     @endforeach 
     </ul> 
    @endif 
@stop 

Answer 1

你從不急於加載任何東西，這就是爲什麼你可能面臨n + 1問題。 如果我明白你的意思，這裏的代碼有點困難，你想要給所有藝術家的歌曲加上$ name的歌曲，對吧？

因此，這裏是你需要做它的工作一切：

// controller 
public function index($name) 
{ 
    // with('songs') is eager loading related songs for you 
    $this->data['artist'] = Artist::with('songs')->whereName($name)->first(); 

    $this->layout->content = View::make('artists.index', $this->data); 
} 

// the problem of your queries is in the helper: 
function link_to_artist_song(Song $song) 
{ 
    return link_to_route('artist.songs.show', $song->title, [ 
     $song->artist->name, // this is calling db query for each song to retrieve its artist (despite it is always the same) 
     $song->id]); 
} 

// so instead use this in your view 
@foreach($artist->songs as $song) 
    <li class="list-group-item"> 
    {{ link_to_route('artist.songs.show', $song->title, [$artist->name, $song->id]) }} 
    </li> 
@endforeach 

Answer 2

當你有大量的歌手與許多藝術家的歌曲存在n + 1問題。它必須獲得所有歌曲（1個查詢），然後爲每首歌曲獲取藝術家（n個查詢）。

在這種情況下，您已經知道該歌曲，所以這是一個查詢，那麼您需要該歌曲的所有藝術家，這只是一個額外的查詢。

只有當你試圖找到某種流派的歌曲時，n + 1問題纔會起作用，例如，它可能會返回很多歌曲。然後，對於每首歌曲，您必須進行額外的查詢以獲取該歌曲的藝術家。這將是急切加載最有用的地方。

$song = Song::find($id); 
$artist = $song->artist; 

Answer 3

你搶一首歌曲，並做$song->artist它會做一個查詢每次。您可以使用Query scopes。

class Song extends Eloquent { 

    public function scopeByArtist($query, $name) { 
     return Artist::whereName($name)->first()->songs(); //->with('artist'); 
    } 
} 

像這個藝術家已經被加載。

查詢有：

$songs = Song::byArtist($name)->get();