Django model validation, pass current value to function?

Question

I'm trying to validate an expected IP value in my Django model as per the below:

dmvpn_dsl = models.GenericIPAddressField(protocol='IPv4', verbose_name="DMVPN DSL IP", \
            validators=[validate_dmvpn_ip('','172.16.100.')], blank=True, null=True)

and in my functions i have

def validate_dmvpn_ip(value,subnet):
    from django.core.exceptions import ValidationError
    if subnet not in value or value != '0.0.0.0':
        raise ValidationError(u'Invalid IP address, please check corrent octects have been assigned')

i just need to pass the current value to the function to check it, but am not sure how to set this?

Thanks

Why not to move subnet into validation function if it's hardcoded anyway? Then you can have just validators=[validate_dmvpn_ip] — zelenyjan, Apr 18 '17 at 12:40

score 1 · Accepted Answer · edited May 23 '17 at 12:02

When you're doing validators=[validate_dmvpn_ip('','172.16.100.')], you end up with the return value of calling the validation function as the validator (which is validators=[None] because you're not returning anything). It looks like you're trying to create a customizable validation function. For that you'll need to write a function that returns a another:

def validate_dmvpn_ip(subnet):
    from django.core.exceptions import ValidationError

    def validator(value):
        if subnet not in value or value != '0.0.0.0':
            raise ValidationError('Invalid IP address, please check corrent octects have been assigned')

    return validator

And you use it like so:

# outside model:
main_validator = validate_dmvpn_ip('172.16.100.')
main_validator.__name__ = 'main_validator'
main_validator.__module__ = 'path.to.this.module'

# inside model
dmvpn_dsl = models.GenericIPAddressField(protocol='IPv4', verbose_name="DMVPN DSL IP", \
    validators=[main_validator], blank=True, null=True)

The outer function returns another function that takes a value to validate, but still has access to the subnet to validate against.

Notice how I'm signing the validator to another variable and assigning the __name__ and __module__ attributes. While this is normally not needed, django needs to be able to refer to the validator directly for migration purposes, and a returned function is not assigned anywhere. Of course if you only have one such validator, you can hardcode the subnet and avoid this mess:

def validate_dmvpn_ip(value):
    subnet = '172.16.100.'
    from django.core.exceptions import ValidationError

    if subnet not in value or value != '0.0.0.0':
        raise ValidationError('Invalid IP address, please check corrent octects have been assigned')

and

dmvpn_dsl = models.GenericIPAddressField(protocol='IPv4', verbose_name="DMVPN DSL IP", \
    validators=[validate_dmvpn_ip], blank=True, null=True)

To learn more about nested functions (closures), take a look at decorators in python which are basically this + special @ syntax.

Thanks!, the path.to.this.module value, I'm not sure what i need to set this to? i will use this validator for multiple subnet validations, which is why i couldn't hard code it, but thank you for the explanations of it all, it helps! — AlexW, Apr 19 '17 at 06:28
It's just the path to the current module. In fact, I think you can just set it to `__name__` which is the magic variable containing the value you want. — Anonymous, Apr 19 '17 at 08:41
dmvpn_dsl = validate_dmvpn_ip('172.16.100.') dmvpn_dsl.__name__ = 'dmvpn_dsl' dmvpn_dsl.__module__ = dmvpn_dsl.__name__ gives, __name__ must be set to a string — AlexW, Apr 19 '17 at 08:54
its working, but i think my logic statement is wrong, if subnet not in value or value != '0.0.0.0': is returning false if the subnet is 172.16.100. or 0.0.0.0 I'm trying to allow either of those values — AlexW, Apr 19 '17 at 12:28

Django model validation, pass current value to function?

1 Answers1