如何计算没有N + 1问题并加载整个模型的雄辩关系？

Question

I am showing a list of categories, and the article count within each category. I get the expected result, but I am having the N+1 problem.

My CategoriesController index function:

public function index()
{
    return View::make('categories.index', [
        'articleCategories' => Category::where('type', 'articles')->orderBy('name')->get(),
    ]);
}

The Category model has many relationship to articles:

public function articles()
{
    return $this->hasMany('Article');
}

My categories.index view:

@foreach($articleCategories as $articleCategory)
    <p>
    {{ HTML::link(URL::route('articles.category', array('category' => Str::slug($articleCategory->name))), $articleCategory->name) }}
    {{ $articleCategory->articles->count() }}
    </p>
@endforeach

Edit: It works if I eager load all related articles, but since I only need the article count pr category this seems overkill. Will eager loading articles and do ->count() impact performance? Or is this the best way to do it?

Answer 1

// helper relation
public function articlesCount()
{
    return $this->hasOne('Article')->selectRaw('category_id, count(*) as aggregate')->groupBy('category_id');
}

// and accessor for fetching it easier
public function getArticlesCountAttribute()
{
    if ( ! array_key_exists('articlesCount', $this->relations)) $this->load('articlesCount');

    return $this->getRelation('articlesCount')->aggregate;
}

Then you can do this:

// eager load in single query
$categories = Category::with('articlesCount')->get();

// thanks to accessor this will return value and load relation only if needed
$categories->first()->articlesCount;