ldc-com-app-bo/app/Models/Contacts.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class Contacts extends Model
{
    public $incrementing = false;
    protected $appends = ['owner_name'];

    public function getOwnerNameAttribute() {
        $owner = AppUser::find($this->user_id);
        return $owner->surname . " " . $owner->firstname;
    }

    public function app_user()
    {
        return $this->belongsTo(AppUser::class, 'id', 'user_id');
    }
}