覆盖ModelForm.save不会更新所有受影响的字段

Question

我想将货币金额作为整数存储在数据库中。为了方便起见，我还添加了float字段：

# 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() 

为了方便起见，我覆盖了我的ModelForm派生程序中的保存方法。它应该自动更新基于amount_btc和amount_eur一些相关的字段：

# 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'] 

现在增加一个新的transaction按预期工作与is_bid和其他dependend领域设置正确。但是，编辑现有条目会导致只更新一个字段。例如。既不price_per_btc也不amount_eur_milicent改变，即使amount_eur是（见下文）：

# 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']) 

我试过instance.save(update_fields=None)，但它并没有任何效果可言。想法？

Answer 1

事务实例将不会修改这种方式，你应该叫form.save（）显式地（引起形式实际上包含更改的数据）

transaction = Transaction.objects.get(id=id) 
form = TransactionForm(request.POST, instance=transaction) 
if form.is_valid(): 
    form.save() 

你不会创建新的对象，只需编辑现有的一个，因为对象主键不会改变