How to calculate with money fields? Like extracting discount percentage

Question

Maybe I'm overlooking something, but can't find a solution on the interwebs..

I have 2 (money) fields: product.price and product.oldPrice

When I try to calculate the discount like this (I'm aware that this simple approach shouldn't work):

{% set discount = product.price / product.oldPrice * 100 %}

I get this error message: Unsupported operand types: Money\Money / Money\Money

And when I try calling it as a 'float':

{% set discount = product.price|number_format(2) / product.oldPrice|number_format(2) * 100 %} 

I get this error message: Object of class Money\Money could not be converted to float

The only solution I can think of is changing the field type in 'Float', but that would make things more difficult.

I also tried Martin Spains solution, who suggested to call the value of the objects like this:

{% set discount = product.price.value / product.oldPrice.value * 100 %}

But then I get this error:

Neither the property "value" nor one of the methods "value()", "getvalue()"/"isvalue()"/"hasvalue()" or "__call()" exist and have public access in class "Money\Money".

I hope someone has a solution for me

Answer 1

As always, for anything non-trivial, you're probably better off writing a Twig extension to abstract your logic to PHP...

That said, for "quick and dirty" calculations, Money objects have an amount property that will give you the value (but as a string, and in cents). It's pretty easy to parse that to something more useful though:

{# get the value of a money field as a float #}
{% set value = moneyField.amount | float / 100 %}

You can then do whatever math operations you need to do, before piping through the currency filter for formatting:

{{ value | currency('USD') }}

You can also use the Money object's currency property if you need to dynamically determine the currency from the field:

{{ value | currency(moneyField.currency) }}