模型字段的随机/非恒定默认值? [英] Random/non-constant default value for model field?

问题描述

我有一个看起来像这样的模型

I've got a model that looks something like this

class SecretKey(Model):
    user = ForeignKey('User', related_name='secret_keys')
    created = DateTimeField(auto_now_add=True)
    updated = DateTimeField(auto_now=True)
    key = CharField(max_length=16, default=randstr(length=16))
    purpose = PositiveIntegerField(choices=SecretKeyPurposes)
    expiry_date = DateTimeField(default=datetime.datetime.now()+datetime.timedelta(days=7), null=True, blank=True)

您会注意到， key 的默认值是一个随机的16个字符的字符串.问题是，我认为此值已被缓存并连续使用多次.有什么办法可以让我每次都得到一个不同的字符串吗?(我不在乎唯一性/冲突)

You'll notice that the default value for key is a random 16-character string. Problem is, I think this value is getting cached and being used several times in a row. Is there any way I can get a different string every time? (I don't care about uniqueness/collisions)

推荐答案

是的，仅在初始化模型元类时才会设置默认值，而在创建SecretKey的新实例时则不会设置默认值.

Yes, the default will only be set when the Model metaclass is initialized, not when you create a new instance of SecretKey.

一种解决方案是将默认值设置为可调用，在这种情况下，每次创建新实例时都会调用该函数.

A solution is to make the default value a callable, in which case the function will be called each time a new instance is created.

def my_random_key():
    return randstr(16)

class SecretKey(Model):
    key = CharField(max_length=16, default=my_random_key)

您当然也可以在模型的 __ init __ 函数中设置值，但是可调用函数更简洁，并且仍可以使用 model = SecretKey(key ='blah').

You could, of course, also set the value in the model's __init__ function, but callables are cleaner and will still work with standard syntax like model = SecretKey(key='blah').

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