PHP/Laravel date based ID – how to make it waterproof?

I want to create a date based ticket ID for my Laravel system, like:

2103 0001
2103 0002
2103 0003

And then next month:

2104 0001
2104 0002
2104 0003

I’ve getted it working using this:

$date = Carbon::now();
$repairCount = Repair::where('code', 'LIKE', date('ym') . ' %')->count();
$repairCount++;

$repairID = $date->format('ym') . " " . str_pad($repairCount,4,"0",STR_PAD_LEFT);

But this isn’t completely ‘waterproof’. When I delete a repair (not the last one). It counts the numbers and then takes the last one (so you get duplicate ID).

How to improve this?

Answer

Ok, I think I covered any issues completely, by using this (based on last()):

$date = Carbon::now();
$repairID = Repair::where('code', 'LIKE', date('ym') . ' %')->get()->last();
if ($repairID != null) 
{
    $repairID = substr($repairID->code, 5);
    $repairID++;
}
else
{
    $repairID = 1;
}

Then save it with:

$date->format('ym') . " " . str_pad($repairID,4,"0",STR_PAD_LEFT)

Please let me know if this can cause some unwanted/unexpected behaviour.