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如何向 Django 中的 model 字段添加自定义方法?

[英]How to add a custom method to a model field in Django?

I have two models that will use the same CardNumberField() to store credit card numbers.我有两个模型将使用相同的CardNumberField()来存储信用卡号。 How can I add a custom method to the field to mask the card numbers?如何在字段中添加自定义方法来屏蔽卡号?

I have created the CardNumberField() which inherits from models.Charfield :我创建了继承自models.CharfieldCardNumberField()

# CARD NUMBER FIELD
class CardNumberField(models.CharField):
    description = _('card number')

    def __init__(self, *args, **kwargs):
        kwargs['max_length'] = 19
        super().__init__(*args, **kwargs)

The CardNumberField() is then imported and used in my customers/models.py :然后将CardNumberField()导入并在我的customers/models.py中使用:

# CARD MODEL
class Card(models.Model):
    number = CardNumberField()
    ...

    def __str__(self):
        return 'Card [{number}]'.format(number=self.number)

...and in my transactions/models.py : ...在我的transactions/models.py 中

# TRANSACTION MODEL
class Transaction(models.Model):
    card_number = CardNumberField()
    ...

    def __str__(self):
        return 'Transaction ...'

So, how can I add the following method to my CardNumberField() to be used by both of my models?那么,如何将以下方法添加到我的CardNumberField()以供我的两个模型使用?

def masked_number(self):
    # display masked card number
    number = self.number
    return number[-4:].rjust(len(number), '#')

Also, how will I grab this field method in a DRF serializer class?另外,我将如何在 DRF 序列化器 class 中获取此字段方法?

Use an abstract model instead, making a field subclass is useful to create completely new columns types, not for this purpose.使用抽象 model 代替,制作字段子类对于创建全新的列类型很有用,而不是为此目的。

class ModelWithCardNumber(models.Model):
   card_number = models.CharField(max_length=19)
   
   @property
   def masked_number(self):
      return self.card_number[-4:].rjust(len(number), '#')
   
   class Meta:
      abstract = True


class Card(ModelWithCardNumber):
    def __str__(self):
        return 'Card [{number}]'.format(number=self.number)


class Transaction(ModelWithCardNumber):
    def __str__(self):
        return 'Transaction ...'

Now in your serializer you can access Card.masked_number and Transaction.masked_number .现在在您的序列化程序中,您可以访问Card.masked_numberTransaction.masked_number

You can override the contribute_to_class method to not only contribute the field, but also include an extra method:您可以覆盖contribute_to_class方法,不仅可以贡献该字段,还可以包含一个额外的方法:

from functools import partialmethod

def _mask_number(self, field):
    number = getattr(self, field.attname)
    return number[-4:].rjust(len(number), '#')

# CARD NUMBER FIELD
class CardNumberField(models.CharField):
    description = _('card number')

    def __init__(self, *args, **kwargs):
        kwargs['max_length'] = 19
        super().__init__(*args, **kwargs)

    def contribute_to_class(self, cls, name, **kwargs):
        super().contribute_to_class(cls, name, **kwargs)
        setattr(
            cls, f'masked_{self.name}',
            partialmethod(_mask_number, field=self)
        )

If you add a field foo to a model class, it will automatically add a masked_ foo method to that class.如果将字段foo添加到 model class 中,它将自动向该 class 添加masked_ foo方法。 This thus also means that if you have two or more CardNumberField s, it will add two or more masked_ foo methods.因此,这也意味着如果您有两个或更多CardNumberField ,它将添加两个或更多masked_ foo方法。

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