This is necessary for credit forms, because it is “just” an invoice with
a negative amount, usually the inverse of an invoice that has to be
rectified. This is a requirement for electronic invoicing too.
However, it is not the only use case: sometimes it is necessary to have
some lines with a negative quantity, even if the total is positive, to
emphasize discounts or to register expenses, like bank commissions in
autoinvoices.
Part of #61.
I had to use a deferrable foreign key because the payment methods have
a reference to the company, and the company now a circular reference to
payment method.
We want to show the percentage of the tax as columns in the invoice,
but until now it was not possible to have a single VAT column when
products have different VAT (e.g., 4 % and 10 %), because, as far
as the application is concerned, these where ”different taxes”. We
also think it would be hard later on to compute the tax due to the
government.
So, tax classes is just a taxonomy to be able to have different names
and rates for the same type of tax, mostly VAT and retention in our
case.
jordi fita mas