python - 如何在创建另一个模型后更新相关模型？

Question

我需要在创建交易时自动更新我的帐户的金额。

我有 Transaction 模型的 model.py:

class Transaction(models.Model):
    user = models.ForeignKey(User, default=None)
    account = models.ForeignKey(Account, default=None)
    ...

它的serializers.py:

class TransactionSerializer(serializers.ModelSerializer):
    class Meta:
        model = Transaction
        fields = ('id', 'user', 'account_id', 'category_id', 'name', 'amount', 'description', 'created_at')

    def create(self, validated_data):
        return Transaction.objects.create(**validated_data)

及其views.py:

class TransactionList(APIView):
    def get(self, request):
        user_id = request.user.pk
        transactions = Transaction.objects.filter(user_id=user_id).order_by('-created_at')
        serializer = TransactionSerializer(transactions, many=True)

        return Response(serializer.data)

    def post(self, request):
        account_id = request.data['account_id']
        category_id = request.data['category_id']
        serializer = TransactionSerializer(data=request.data)

        if serializer.is_valid():
            serializer.save(user=request.user, account_id=account_id, category_id=category_id)

            self.update_account(request)

            return Response(serializer.data, status=HTTP_201_CREATED)

        return Response(serializer.errors, status=HTTP_400_BAD_REQUEST)

    def update_account(self, request):
        account_id = request.data['account_id']
        category_id = request.data['category_id']
        account = Account.objects.get(pk=account_id)
        category = Category.objects.get(pk=category_id)

        if category.type == 'expense':
            account.amount = (account.amount - int(self.request['amount']))
        else:
            account.amount = (account.amount + int(self.request['amount']))

        # Then what?

我想创建一个自定义方法，如果 serializer 有效，它将在条件下执行，这将通过它们的 id 获取帐户和类别。到目前为止，我可以显示它们的当前值，例如 amount 和 name，但在那之后，我不知道该怎么做。我想我需要使用我的 AccountSerializer，但我不确定。

Answer 1

最简单的方法是覆盖 Transaction 模型的 save 方法:

class Transaction(models.Model):
    user = models.ForeignKey(User, default=None)
    account = models.ForeignKey(Account, default=None)
    ...
    def save(self, *args, **kwargs):
        super(Transaction, self).save(*args, **kwargs)
        # Update self.account

参见 Django documentation了解详情。