我被要求返回这个json，我正在使用Laravel中的api资源：

{
  "data": [
    {
      "type": "users",
      "id": "1",
      "attributes": {
        "name": "test name",
        "lastname": "test lastname"
        "projects": 2
      },
      "relationships": {
        "projects": {
          "data": [
            {
              "id": 1,
              "type": "projects"
            }
          ]
        }
      }
    }
  ],
  "included": [
    {
      "type": "projects",
      "id": 1,
      "attributes": {
        "title" : "Test",
        "description": "Test",
        ....
        ....
      }
    }
  ]
}

一个用户有许多项目，我是这样做的：
ProjectCollection.php

<?php

namespace App\Http\Resources;

use Illuminate\Http\Resources\Json\ResourceCollection;

class ProjectCollection extends ResourceCollection
{ 
    public function toArray($request)
    {         
        return [
            'data' => $this->collection
        ];
    }  
}

ProjectResource.php

<?php

namespace App\Http\Resources;

use Illuminate\Http\Resources\Json\JsonResource;

class ProjectResource extends JsonResource
{
    public function toArray($request)
    {
        return [
            "type" => "projects",
            "id" => $this->id,
            "attributes" => [
                "title" => $this->title,
                "description" => $this->description,
                ....
                ....   
            ]
        ];
    }
}

UserCollection.php

<?php

namespace App\Http\Resources;

use Illuminate\Http\Resources\Json\ResourceCollection;

class UserCollection extends ResourceCollection
{
    public function toArray($request)
    {
        return [
            'data' => $this->collection
        ];
    }

    public function with($request)
    {

        return [
            //'included' => ProjectResource::collection($this->collection->map->only(['firstProject'])  it doesn't work
            'included' => new ProjectCollection($this->collection->map->only(['firstProject']) // it doesn't work
        ];
    }
}

UserResource.php

<?php

namespace App\Http\Resources;

use Illuminate\Http\Resources\Json\JsonResource;

class UserResource extends JsonResource
{
    public function toArray($request)
    {
        
        return [
            "type" => "users",
            "id" => $this->id,
            "attributes" => [
                "name" => $this->name,
                "lastname" => $this->lastname
                "projects" => $this->whenCounted('projects')
            ],
            "relationships" => [
                "projects" => new ProjectCollection($this->firstProject),
            ]            
        ];
    }
}

Models/User.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Support\Str;

class User extends Model
{
    use HasFactory;

    protected $guarded = ['id'];   

    public function projects()
    {
        return $this->hasMany(Project::class);
    }

    public function firstProject()
    {
        return $this->projects()->oldest()->limit(1);
    }
}

UsersController.php

$users = User::withCount('projects')->latest()->get();

    return new UserCollection($users);

我收到此错误：
PHP 8.1.1 9.39.0试图读取数组中的属性“id”
我能做什么？谢谢。