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I am implementing a plugin for a client that will use the 'Max Sale Quantity' value of a Magento Stock Item on a product as a means of setting an upper-bound on total customer purchases.

Because I need to check this condition in multiple events, controller actions, I cannot contain it to merely an Observer where I could create a local protected function that checks this condition from my Resource Model.

In my requirements I will be limiting the cart additions. But I find myself in a dilemma: from the controller addAction I need to rely on throw - however from sales_quote_merge_before it seems that I could effectively unset the offending products and post a message to the customer/session, though, I could throw and catch, respectively as with the controller action instead.

My questions are:

  • Is this bad practice to effectively rely on throw from the module helper?
  • Is this, rather, a model method that I need to invoke?
  • What is the best design strategy that allows me to keep my module DRY?

Edit:

As of EE 1.12 I see only 4 instances of Helper/Data.php files that throw - 3 of them are Api2/Oauth. Mage/Core does it once as well, but this seems to be the only other instance. Various 3rd parties look like they take different approaches here.

Any feedback is welcome.

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  • I think, generally, it's bad to use Exceptions for program logic control rather than actually handling 'Exceptional' circumstances. If you can solve the problem and avoid having to throw Exceptions to do it, I think that will lead to a 'better' solution. Sometimes though, you have to just deal with what the Framework gives you to work with... – Aaron Bonner Feb 28 '13 at 8:00
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Saying to the customer, "we are sorry, you can't purchase so much" is a exception. The expected case is, there is enough and you put the products in the cart. And one more word: There are try and catch blocks inside of magento, for example in \Mage_Checkout_CartController::addAction:

// [...]
} catch (Mage_Core_Exception $e) {
        if ($this->_getSession()->getUseNotice(true)) {
            $this->_getSession()->addNotice(Mage::helper('core')->escapeHtml($e->getMessage()));
// [...]

Let me say it this way: They are there to be used :-)

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