在Laravel中如何按关系过滤？

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class User extends Model
{
    public function posts()
    {
        return $this->hasMany(Post::class);
    }
}

class Post extends Model
{
    public function user()
    {
        return $this->belongsTo(User::class);
    }
}

<?php

use App\User;

$userId = 1;

$user = User::with(['posts' => function ($query) {
    // 在这里进行关系过滤
    $query->where('category', 'news');
}])->find($userId);

// 获取过滤后的文章
$filteredPosts = $user->posts;