autocde2.0/app/Http/Resources/API/RequirementGroupResource.php

<?php

namespace App\Http\Resources\API;

use App\Models\RequirementGroup;
use Illuminate\Http\Request;
use Illuminate\Http\Resources\Json\JsonResource;

class RequirementGroupResource extends JsonResource
{
    /**
     * Transform the resource into an array.
     *
     * @return array<string, mixed>
     */
    public function toArray(Request $request): array
    {
        //return parent::toArray($request);
        return[
            'id'=>$this->id,
            'name'=>$this->name,
            'asset_id'=>$this->asset_id,
            'abbr_name'=>$this->abbr_name,
            'parent_id' => $this->parent_id,
            //'children' =>$this->parent_id == 0 ? RequirementGroupResource::collection($this->children) : [],
            'children' =>$this->when($this->children->isNotEmpty(),function (){
                return $this->children->map(function ($child){
                    return new RequirementGroupResource($child);
                })->all();
            })
        ];
    }
}