laravel 5.1 以多对多关系获取每个类别的相关 5 条新闻

Question

我被困在这里已经尝试了 2-3 个小时。

我有一个多对多关系：

class Category extends Model
{
    public function news()
    {
        return $this->belongsToMany('App\News');
    }
}  

class News extends Model
{
    public function categories()
    {
        return $this->belongsToMany('App\Category');
    }
}

我正在尝试获取相关类别的最新 5 条新闻：

$front_categories = Category::with(array(
        'news'=>function($query){
        $query->where('publish','1')->orderBy('created_at', 'desc')->take(5);}))
       ->where('in_front', 1)->get();

上面的查询对我不起作用，它给出了总共五个结果，而不是每个类别的 5 个结果。

Answer 1

我认为，因为您确实急切地加载了一个包含多个记录的集合。

求解需要循环

$front_categories = Category::where('in_front', 1)->get();

foreach ($front_categories as $fCategory) {
    $fCategory->load(['news' => function($query) {
        $query->where('publish','1')->orderBy('created_at', 'desc')->take(5);
    }]);
}

此解决方案将对数据库执行许多查询。如果您只想处理 1 个查询，请查看此 Using LIMIT within GROUP BY to get N results per group?

Answer 2

根据我对Laravel的了解，您可以尝试这样做。

class Category {

    public function recentNews()
    {
        return $this->news()->orderBy('created_by', 'DESC')
                            ->take(5);
    }
}

// Get your categories
$front_categories = Category::where('in_front', 1)->get();

// load the recent news for each category, this will be lazy loaded
// inside any loop that it's used in.
foreach ($front_categories as $category) {
    $category->recentNews;
}

这与 Lê Trần Tiến Trung 的回答具有相同的效果，并导致多个查询。它还取决于您是否重用此功能。如果是一次性的，最好将其放在其他地方。其他方法也可以更动态，例如创建一个 returns 类别集合的方法，你可以向它询问某个数字：

class CategoriesRepository {

    public static function getFrontCategories(array $opts = []) {

        $categories = Category::where('in_front', 1)->get();

        if (!empty($opts) && isset($opts['withNewsCount'])) 
        {
            foreach ($categories as $category) 
            {
                $category->recentNews = static::getRecentNewsForCategory(
                    $category->id,
                    $opts['withNewsCount']
                );
            }
        }

        return $categories;
    }
}

$front_categories = CategoriesRepository::getFrontCategories([
    'withNewsCount' => 5
]);

laravel 5.1 以多对多关系获取每个类别的相关 5 条新闻

laravel 5.1 getting related 5 news of each category in many-to-many relation

php

laravel

many-to-many

eager-loading