todo/app/Models/Department.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\HasMany;

class Department extends Model
{
    use HasFactory;

    protected $fillable = [
        'id',
        'name',
        'created_by_id',
    ];

    public function users(): HasMany
    {
        return $this->hasMany(User::class);
    }

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