Sunday, August 28, 2016

Re: Validators and django.contrib.postgres.fields JSONField

Ah! Fantastic! I love it when I make a dumb mistake because it's an easy solution!

Instead of:
class DummyModel(models.Model):
= JSONField(validators = [TestValidator])#Using class, wrong!

I should be doing:

class DummyModel(models.Model):
= JSONField(validators = [TestValidator()])#Using instance of class, right!

As for using a class as a validator, I am performing some complex validation on the data inside the JSON to ensure it adheres to a specific format above and beyond the normal JSON validation, so a class based validator seemed like the right way to go. I based this off things like the Regex validator in django.core.validators found here: Perhaps this wasn't the right approach?

Thanks for your help!
-Ryan Causey

On Sunday, August 28, 2016 at 3:46:31 AM UTC-7, Daniel Roseman wrote:
On Sunday, 28 August 2016 07:54:47 UTC+1, Ryan Causey wrote:
So I've dug into this a little more, and I've come up with the debugger trace below.

-> dummyModelInstance.full_clean()
:\program files\python35\lib\site-packages\django\db\models\
-> self.clean_fields(exclude=exclude)
:\program files\python35\lib\site-packages\django\db\models\
-> setattr(self, f.attname, f.clean(raw_value, self))
:\program files\python35\lib\site-packages\django\db\models\fields\
-> self.run_validators(value)
:\program files\python35\lib\site-packages\django\db\models\fields\
-> v(value)
> c:\program files\python35\lib\site-packages\django\utils\
-> def __new__(cls, *args, **kwargs):
(Pdb) ll
16  ->         def __new__(cls, *args, **kwargs):
17                 # We capture the arguments to make returning them trivial
18                 obj = super(klass, cls).__new__(cls)
19                 obj._constructor_args = (args, kwargs)
20                 return obj

For some reason, when run_validators() calls the custom TestValidator, it seems that a TestValidator object is constructed rather than entering the __call__() method of the class. I can't see a reason for this to happen, so what am I doing wrong here?

-Ryan Causey

This isn't anything to do with JSONFields, but your misunderstanding about what callables are and what `__call__` does. That is not a class method, but an instance method; calling a class merely instantiates it (as you should expect). Whatever is passed as a validator is called; if it's a function, it will be executed, if it's an instance, its `__call__` method will be called, but if it's a class it will be instantiated.

I'm not sure why you are passing a class at all here. Normally a validator is a method; if you need a class for some reason then you should pass an *instance* of that class, not the class itself.

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