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Laravel 8 关联模型计数

2021-07-08 09:44:46 更新

如果想要只计算关联结果的统计数量而不需要真实加载它们,可以使用 withCount 方法,它将放在结果模型的 {relation}_count 列。示例如下:

$posts = App\Models\Post::withCount('comments')->get();

foreach ($posts as $post) {
    echo $post->comments_count;
} 

可以像给查询添加限制一样为多个关系添加「计数」:

use Illuminate\Database\Eloquent\Builder;

$posts = App\Models\Post::withCount(['votes', 'comments' => function (Builder $query) {
    $query->where('content', 'like', 'foo%');
}])->get();

echo $posts[0]->votes_count;
echo $posts[0]->comments_count; 

还可以给关联计数结果起别名,这允许你在同一关联上添加多个计数:

use Illuminate\Database\Eloquent\Builder;

$posts = App\Models\Post::withCount([
    'comments',
    'comments as pending_comments_count' => function (Builder $query) {
        $query->where('approved', false);
    },
])->get();

echo $posts[0]->comments_count;

echo $posts[0]->pending_comments_count; 

如果将 withCountselect 查询组装在一起,请确保在 select 方法之后调用 withCount

$posts = App\Models\Post::select(['title', 'body'])->withCount('comments')->get();

echo $posts[0]->title;
echo $posts[0]->body;
echo $posts[0]->comments_count; 

此外,使用 loadCount 方法,您可以在父模型被加载后使用关联计数:

$book = App\Models\Book::first();

$book->loadCount('genres'); 

如果您需要在预加载查询上设置额外的查询约束,您可以传递一个希望加载的关联数组。数组值应该是 Closure 实例,它接收查询生成器实例:

$book->loadCount(['reviews' => function ($query) {
    $query->where('rating', 5);
}])