What is the best way to calculate the price from selected line item field (List field or maybe taxonomy) in final price ?

Example: we sell T-shirt. We define a color (list) as line item field, (red, blue, black) Then we want drupal to calculate the price with multiplying to the value specified for selected color. Red = 4 blue = 5 black = 6 The concept is that we don't want to make different product for each option, instead we want to use line item field (Select list) to calculate the price. Maybe for T-shirt doesn't make sense but it fits in our need.

How we can accomplish this and what is the best way of doing it ? Rules or own module ? How we can specify a value for each color option?

I am more interested in coding approach, because there are a lot of different options and we don't want to make many rules for those.

  • Why did you add the field to the line item type and not to the product ( as a product attribute ) Jan 27, 2013 at 21:39
  • The main scenario is more complex than this, we have many attributes and options which doesn't make sense to make a product for each different option match. it makes more sense to just calculate it with line_item_field(). I already solved the problem, will send the solution after 3 hours. I will be happy to hear your opinions about my solution. Thanks Jan 27, 2013 at 23:33

1 Answer 1


The only reason I used following solution, was because we didn't need to make a product type for variety of options we had, and we had a lot of options which didn't make sense to make it as individual product.

I used rules, if any one find better solution let me know, hope it will help someone.

1) defined an action function to multiply the price to a coefficient

2) checked to see what option has been selected and proper coefficient has been applied

 * Rules action: multiply the unit price by some amount.
function modulename_unit_price_multiply($line_item, $amount, $component_name, $round_mode) {
  if (is_numeric($amount)) {       
    // Coefficient variable
    $cf = '1';
        $selected_color = $line_item->field_color[LANGUAGE_NONE][0]['value'];
        switch ($selected_color){
            case 'red': 
                $cf *= 2;
            case 'black':
                $cf *= 3;
           case 'blue':
                $cf *= 4;
    } else {
        $cf *= '1';
    $wrapper = entity_metadata_wrapper('commerce_line_item', $line_item);
    $unit_price = commerce_price_wrapper_value($wrapper, 'commerce_unit_price', TRUE);

    // Calculate the updated amount and create a price array representing the
    // difference between it and the current amount.
    $current_amount = $unit_price['amount'];
    $updated_amount = commerce_round($round_mode, $current_amount * $amount * $cf);

    $difference = array(
      'amount' => $updated_amount - $current_amount,
      'currency_code' => $unit_price['currency_code'],
      'data' => array(),

    // Set the amount of the unit price and add the difference as a component.
    $wrapper->commerce_unit_price->amount = $updated_amount;

    $wrapper->commerce_unit_price->data = commerce_price_component_add(

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