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.
They are not functions because i need to join them with the main
invoice relation, and although possible is a bit more awkward with
functions.
The taxes have their own relation because i will need them grouped by
their name in the PDF, so it will probably be a select for that
relation.
jordi fita mas