On Mar 1, 2011, at 11:35, lirc201 wrote:
> I like the example on the weblink which is just using MySQL
> functionality, it is very clever. Thanks for the help and push. My
> code is working! I did like the security tricks I discovered for my
> updates below to only pass a field list.
>
> function updateInventory($id, $quantity) {
> $inv = $this->getQuantity($id); <- function is in the same
> model
> $this->data['Model']['id'] = $id;
> $this->data['Model']['inventory'] = $inv + $quantity;
> if($this->save($this->data, array(
> 'validate' => 'false',
> 'fieldList' => array('id',
> 'inventory')))) {
> ... logic for return values ...
> }
> }
This is not atomic. Between the line where you get the current quantity and the
line where you save the updated quantity, someone else might have updated the
quantity, and you'd be wiping out their change. Consider two managers
simultaneously adding 5 to the inventory of the same item. The expected result
would be that in the end the inventory is incremented by 10, but because of the
race condition in your code, it might only be incremented by 5.
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