I want to store money amounts as integers in the database. For convenience I added float fields as well:
# File: models.py
class Transaction(models.Model):
user = models.ForeignKey(User, related_name='transactions')
date = models.DateTimeField(default=datetime.now)
# transacted btc-amount in satoshi; positive when I bought btc, negative else
amount_btc_satoshi = models.IntegerField()
# for convenience: transacted btc-amout in units of 1 btc
amount_btc = models.FloatField(null=True)
# transacted fiat-amount in 1e-5 euros; positive when I sold btc, negative else
amount_eur_milicent = models.IntegerField()
# for convenience: transacted fiat-amout in units of 1 eur
amount_eur = models.FloatField(null=True)
# True if I bought bitcoins, False if I sold bitcoins
is_bid = models.BooleanField()
# effective fiat price per 1 BTC in EUR
price_per_btc = models.FloatField()
For convenience I overrode the save method in my ModelForm derivate. It is supposed to automatically update some dependent fields based on amount_btc
and amount_eur
:
# File: forms.py
class TransactionForm(forms.ModelForm):
def clean(self):
cleaned_data = super(TransactionForm, self).clean()
if cleaned_data['amount_btc'] > 0. and cleaned_data['amount_eur'] > 0.:
raise forms.ValidationError('Either BTC amount or fiat amount must be negative.')
return cleaned_data
def save(self, commit=True, *args, **kwargs):
instance = super(TransactionForm, self).save(commit=False, *args, **kwargs)
# store input data in integer format
instance.amount_btc_satoshi = int(round(self.cleaned_data['amount_btc'] * 1e8))
instance.amount_eur_milicent = int(round(self.cleaned_data['amount_eur'] * 1e5))
# provide convenient amounts
instance.amount_btc = instance.amount_btc_satoshi / 1e8
instance.amount_eur = instance.amount_eur_milicent / 1e5
instance.is_bid = instance.amount_btc_satoshi > 0
instance.price_per_btc = -1. * instance.amount_eur / instance.amount_btc
if commit:
instance.save()
return instance
class Meta:
model = Transaction
fields = ['date', 'amount_btc', 'amount_eur']
Now adding a new transaction
works as expected with is_bid
and the other dependend fields properly set. However, editing an existing entry results in the update of only one field. E.g. neither price_per_btc
nor amount_eur_milicent
is changed even if amount_eur
is (see below):
# File: views.py
@login_required
def transaction_add(request):
form = TransactionForm(request.POST)
if form.is_valid():
transaction = form.save(commit=False)
transaction.user = request.user
transaction.save()
else:
messages.error(request, ';'.join('{}: {}'.format(key, value) for key, value in form.errors.items()))
return redirect(request.POST['next'])
@login_required
def transaction_edit(request, id):
transaction = Transaction.objects.get(id=id)
form = TransactionForm(request.POST, instance=transaction)
if form.is_valid():
transaction.save()
else:
messages.error(request, ';'.join('{}: {}'.format(key, value) for key, value in form.errors.items()))
return redirect(request.POST['next'])
I tried instance.save(update_fields=None)
, but it did not have any effect at all. Ideas?