Django decimal field fails to store floating numbers that should be ok

user_79470 0
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In a django project I'm trying to store a calculated decimal value, but it fails for some strange reason. My model looks something like:

class FancyModel(models.Model):
  fancy_field = models.DecimalField(max_digits=10, decimal_places=3, null=True, blank=True)

Sometimes, rather often actually, it crashes on save:

django.db.utils.IntegrityError: CHECK constraint failed: myapp_fancy_model

which I found out after some digging was caused by this validation:

django.core.exceptions.ValidationError: {'fancy_field': ['Ensure that there are no more than 2 decimal places.']}

I've dumped the values of the actual model, and it seems ok to me:

{'fancy_field': 3.26 }

I cannot see how this would fail. Sometimes it works fine, other times it crashes. I've tried to use the round-method, like:

model_instance.fancy_model = round(floating_value, 2) but it still fails.

decimal floating-point rounding django python
2 Answers

After commenting out all the code, then adding one after one line back in, I discovered that the error wasn't caused by the decimalfield at all, but a PositiveIntegerField that got a negative value. The model.full_clean() never mentioned the PositiveIntegerField at all, so this is really weird. That's a few hours I won't get back :-/

user_794700

You should consider changing the decimal_places param passed from 3 to 2

user_99538780
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