laravel APi 资源调用未定义的方法 Illuminate\Database\Query\Builder：：mapInto()

我有一对一的帖子和用户模型，效果很好:

//User.php

public function post(){
    return $this->hasOne(Post::class);
}


// Post.php

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

现在我创建API资源:

php artisan make:resource Post
php artisan make:resource User

I need to return all post with an api call then i set my route:

//web.php: /resource/posts

Route::get('/resource/posts', function () {
    return PostResource::collection(Post::all());
});

这是我的帖子资源课:

<?php

namespace App\Http\Resources;
use Illuminate\Http\Resources\Json\Resource;
use App\Http\Resources\User as UserResource;

class Posts extends Resource
{
/**
 * Transform the resource into an array.
 *
 * @param  \Illuminate\Http\Request  $request
 * @return array
 */
public function toArray($request)
{
      return [
        'id' => $this->id,
        'title' => $this->title,
        'slug' => $this->slug,
        'bodys' => $this->body,
        'users' => UserResource::collection($this->user),
        'published' => $this->published,
        'created_at' => $this->created_at,
        'updated_at' => $this->updated_at,
    ];

}
}

this is the error:

Call to undefined method Illuminate\Database\Query\Builder::mapInto()

如果我删除:

'users' => UserResource::collection($this->user),

这是工作，但我需要在我的API json中包括关系，我已经阅读并关注了https://laravel.com/docs/5.5/collections岁的文档.

这是我的用户资源类:

```

namespace App\Http\Resources;

use Illuminate\Http\Resources\Json\Resource;

class User extends Resource
{
/**
 * Transform the resource into an array.
 *
 * @param  \Illuminate\Http\Request  $request
 * @return array
 */
public function toArray($request)
{
   return [
       'user_id' => $this->user_id,
       'name' => $this->name,
       'lastname' => $this->lastname,
       'email' => $this->email
   ];
}
}

any ideas where am i wrong?