How to create a Django FloatField with maximum and minimum limits?

Question

I'm storing some floating-point data in my Django models, and only a certain range of values are meaningful. Therefore, I'd like to impose these limits at both the model and SQL constraint level.

For example, I'd like to do something like this:

class Foo(Model):    myfloat = FloatField(min=0.0, max=1.0) 

I want to do this at the model level, not the form level. In fact, I might like the form level to have a different range; e.g., use percentages [0,100] at the form level but translate to [0,1] in the model.

Is this possible, and if so, how would I go about doing it?

Answer 1

The answers so far describe how to make forms validate. You can also put validators in the model. Use MinValueValidator and MaxValueValidator.

For example:

from django.core.validators import MaxValueValidator, MinValueValidator  ... weight = models.FloatField(     validators=[MinValueValidator(0.0), MaxValueValidator(1.0)], ) 

EDIT:

However, that does not add a SQL constraint.

You can add SQL constraints as described here as CheckConstraints in Meta.constraints.

Combined example:

from django.core.validators import MaxValueValidator, MinValueValidator from django.db.models import CheckConstraint, Q  class Foo(Model):     myfloat = FloatField(min=0.0, max=1.0,         # for checking in forms         validators=[MinValueValidator(0.0), MaxValueValidator(1.0)],)      class Meta:         constraints = (             # for checking in the DB             CheckConstraint(                 check=Q(myfloat__gte=0.0) & Q(myfloat__lte=1.0),                 name='foo_myfloat_range'),             ) 

Answer 2

If you need constraint on form level you can pass min_value and max_value to form field:

myfloat = forms.FloatField(min_value=0.0, max_value=1.0) 

But if you need to move it up to model level you have to extend base models.FloatField class

class MinMaxFloat(models.FloatField):     def __init__(self, min_value=None, max_value=None, *args, **kwargs):         self.min_value, self.max_value = min_value, max_value         super(MinMaxFloat, self).__init__(*args, **kwargs)      def formfield(self, **kwargs):         defaults = {'min_value': self.min_value, 'max_value' : self.max_value}         defaults.update(kwargs)         return super(MinMaxFloat, self).formfield(**defaults) 

Then you can use it in models

class Foo(models.Model):     myfloat = MinMaxFloat(min_value=0.0, max_value=1.0)