On the invoice I need the total amount in words (i.e. 10 EURO and 50 Cents).

Currently I use the onchange method on the amount_total field. This does converts it into words but is only called once because amount_total is a so-called functional field. This always results in Zero EURO and Zero Cents.

 def onchange_amount(self, cr, uid, ids, amount):
    x_text_amount = amount_to_text_en.amount_to_text(amount, 'en', 'EURO')
    return {'value': {'x_text_amount': x_text_amount}}

In account_invoice.py I need to change an existing function to update my new field amount_in_words. I thought I could update this field when the user validates an invoice. However I did not get this working.

I created the following to function already.

def _compute_amount_letter(self):
    self.x_amount_letter=self._get_amount_letter(self.amount_total)

def _get_amount_letter(self,amount):
    return amount_to_text_en(amount) 

Could you please help me how to change/update account_invoice.py - so that my field amount_in_words will be updated when the user validates the invoice / the total amount changes.

Many thanks!