Custom attribute crashing on toJSON - laravel

Question

I am trying to determine which position the order is in to generate a order id, but this crashes laravel, nothing in the logs, just a 500 error in the browser:
<?php
namespace App;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\SoftDeletes;
class Load extends Model
{
use SoftDeletes;
protected $dates = ['deleted_at'];
protected $guarded = ['id', 'created_at', 'updated_at'];
protected $appends = ['order_no'];
public function workorder()
{
return $this->belongsTo('App\WorkOrder', 'work_order_id');
}
public function getOrderNoAttribute()
{
$count = 1;
foreach ($this->workorder->loads as $load) {
if ($load->id == $this->id) {
break;
}
$count++;
}
return $this->workorder->id . "-" . $count;
}
}
When I changed it to return just an integer it worked, so I am almost certain it is the relation access causing the issue. Is there a way to do this that is better?

Answer 1

Generally while defining calculated attributes, dependence on relationship should be avoided. So one way to achieve what you are trying is (as you mentioned solved) is to get all loads having the same work_orderid and proceed with it.
public function getLoadCountAttribute ()
{
$id = $this->work_order_id;
return static::where('work_order_id', $id)->count();
}
Another way, more logical I guess, would be to define a relationship and eager load
//define a relation in your Load model
public function load_count ()
{
return count($this->workorder->loads)
//-1 if you want to exclude the current load from count
;
}
//Then use Load::with('load_count') to eager load the load_count
//You may also use global scope
Yet another way would be to define a static function on Workorder model, which will accept an id and return the load_count
//Workorder model
public static function getLoadCount($id)
{
$workorder = static::findOrFail($id);
return count($workorder->loads);
}
Hope this helps.