Django查询更新——字段由字符串决定

Question

我想更新一条记录，但是字段是由字符串决定的。可以这样做吗？

这是我的模型：

class Wallet(models.Model):
    user_id = models.IntegerField(blank=True, null=True)
    wallet1 = models.DecimalField(max_digits=15, decimal_places=2, blank=True, null=True)
    wallet2 = models.DecimalField(max_digits=15, decimal_places=2, blank=True, null=True)

这是我的代码：

amount = 200
transfer_from = 'wallet1'
transfer_to = 'wallet2'

obj = Wallet.objects.get(user_id=1)
obj.transfer_from = obj.transfer_from - amount
obj.transfer_to = obj.transfer_to + amount
obj.save()

Django 只在我写这个的时候识别字段：

obj.wallet1 = obj.wallet1 - amount

但它无法识别：

transfer_from = 'wallet1'
obj.transfer_from = obj.transfer_from - amount

表示'Wallet'对象没有属性'transfer_from'。谢谢。

Answer 1

实际上这是一个 Python 问题。请参考：What is getattr() exactly and how do I use it?

使用 getattr，您可以执行以下操作：

transfer_from_label = 'wallet1'
transfer_from = getattr(obj, transfer_from_label)
transfer_from = transfer_from - amount

Answer 2

这没有经过测试，但应该可以。

amount = 200
transfer_from = 'wallet1'
transfer_to = 'wallet2'


obj = Wallet.objects.get(user_id=1)
transfer_from_field_val = getattr(obj,transfer_from)
transfer_to_field_val = getattr(obj,transfer_to)
transfer_from_field_val = transfer_from_field_val - amount
transfer_to_field_val = transfer_to_field_val + amount

setattr(obj , transfer_from, transfer_from_field_val)
setattr(obj , transfer_to, transfer_to_field_val)
obj.save()

Answer 3

setattr(obj, transfer_form, getattr(obj, transfer_form) - amount)

getattr, setattr.

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