Magento 1 - How to get relevant 'tax_calculation_rate_id' from order items

Question

I'm trying to get 'tax_calculation_rate_id' by iterating through ordered products.

The following code works ok, but the problem arises when there are multiple ids assigned to the same percentage values (e.g. "VAT exempt rate" at 0% and "EC Sales rate" at 0%)

Is there a better way to get the rate ids calculated?

Thank you for your help!

// $line_item and $address come as arguments 

$store = Mage::app()->getStore();
$product_class= Mage::getModel('catalog/product')
                         ->loadByAttribute('sku',$line_item->getSku())
                         ->getTaxClassId();
$tax_model = Mage::getSingleton('tax/calculation');
$request = $tax_model->getRateRequest($address, null, null, $store);
$percent = $tax_model->getRate($request->setProductClassId($product_class));

$rates = Mage::getModel("tax/calculation_rate")
                         ->getCollection()
                         ->addFieldToFilter('rate', array('eq'=>$percent));
foreach ($rates as $rate)
{  
    $mage_rate_id = $rate->getTaxCalculationRateId();
    // if more than 1 rate exits it obviously picks the last one
}

Answer 1

I guess, you will need to get the dedicated tax rates not only by percentage but also by code. I would say you can to call $tax_model->getAppliedRates($request->setProductClassId($product_class)) instead of $tax_model->getRate($request->setProductClassId($product_class)). With that call you will get an array with all rates - but as far as I see the tax_calculation_rate_id is not in this array (for what ever reason). Therfore you will need to get the rates with an additional call to $tax_model->getRates($ruleId).

I suppose the code for that would look like this - but I haven't tested it:

$tax_model = Mage::getSingleton('tax/calculation');
$request = $tax_model->getRateRequest($address, null, null, $store);
$appliedRates = $tax_model->getAppliedRates($request->setProductClassId($product_class));

foreach ($appliedRates as $appliedRate){
    foreach ($appliedRate['rates'] as $oneRate){
        //returns an array of all applied rate ids
        $rates = $tax_model->getRates($oneRate['rule_id']);
    }
}

Anyway, I quess alternatively you can get all the data you need by using the following 3 tables: sales_order_tax_item, sales_order_tax and tax_calculation_rate. Each order item has entries for each applied tax rate in sales_order_tax_item, therefore you just need to consider the corresponding rows in that table. This should work, if you have unique codes for your tax rates.

//assuming your parameter $line_item is an order item you can load the entries 
//for that order item from sales_order_tax_item table
$taxItemCollection = Mage::getModel('tax/sales_order_tax_item')
                    ->getCollection()
                    ->addFieldToFilter('item_id', array('eq'=>$line_item->getId()));

//iterate through the collection items and load the corresponding sales_order_tax entry
//and based on that the corresponding tax_calculation_rate entry
foreach ($taxItemCollection as $taxItem) {
    $tax = Mage::getModel('tax/sales_order_tax')->load($taxItem->getTaxId());
    $rate = Mage::getModel("tax/calculation_rate")-loadByCode($tax->getCode());
    $mage_rate_id = $rate->getTaxCalculationRateId();
}