Question

I want to be able to check a variable that I have set in a users session, and based on that make the users cart tax exempt. How can I do this?

I think that messing around with the customer type is going to be too complicated. Is there another way to vary the tax that is applied? Or away to change the customer group on the fly.

Answer 1

I’ve done something very similar to this, I’ve overridden app/code/core/Mage/Tax/Model/Calculation.php as app/code/local/Mage/Tax/Model/Calculation.php and added the statement shown below the comment to set tax rate to 0 based on a session value. This is calculated on the fly at checkout.

public function getRate($request)
{
    if (!$request->getCountryId() || !$request->getCustomerClassId() || !$request->getProductClassId()) {
        return 0;
    }

    $cacheKey = "{$request->getProductClassId()}|{$request->getCustomerClassId()}|{$request->getCountryId()}|{$request->getRegionId()}|{$request->getPostcode()}";
    if (!isset($this->_rateCache[$cacheKey])) {
        $this->unsRateValue();
        $this->unsCalculationProcess();
        $this->unsEventModuleId();
        Mage::dispatchEvent('tax_rate_data_fetch', array('request'=>$this));
        if (!$this->hasRateValue()) {
            $this->setCalculationProcess($this->_getResource()->getCalculationProcess($request));
            $this->setRateValue($this->_getResource()->getRate($request));
        } else {
            $this->setCalculationProcess($this->_formCalculationProcess());
        }
        $this->_rateCache[$cacheKey] = $this->getRateValue();
        $this->_rateCalculationProcess[$cacheKey] = $this->getCalculationProcess();
    }
//this is the bit you're looking for down here
    if (Mage::getStoreConfig('tax/calculation/calc_rate_zero')) {
        $_taxvat = Mage::getSingleton('checkout/session')->getQuote()->getCustomerTaxvat();
        if ( $_taxvat != null && $_taxvat != ' ') {
            $this->setRateValue( 0 );
            $this->_rateCache[$cacheKey] = $this->getrateValue();
            $this->_rateCalculationProcess[$cacheKey]= $this->getCalculationProcess();
        }
    }

    return $this->_rateCache[$cacheKey];
}