How to limit the maximum value of a numeric field in a Django model

Question

Django has various numeric fields available for use in models  e g  DecimalField and PositiveIntegerField  Although the former can be restricted to the number of decimal places stored and the overall number of characters stored  is there any way to restrict it to storing only numbers within a certain range  e g  0 0-5 0    Failing that  is there any way to restrict a PositiveIntegerField to only store  for instance  numbers up to 50   Update  now that Bug 6845 has been closed  this StackOverflow question may be moot  - sampablokuper

User · Accepted Answer

You could also create a custom model field type - see http://docs.djangoproject.com/en/dev/howto/custom-model-fields/#howto-custom-model-fields

In this case, you could 'inherit' from the built-in IntegerField and override its validation logic.

The more I think about this, I realize how useful this would be for many Django apps. Perhaps a IntegerRangeField type could be submitted as a patch for the Django devs to consider adding to trunk.

This is working for me:

from django.db import models

class IntegerRangeField(models.IntegerField):
    def __init__(self, verbose_name=None, name=None, min_value=None, max_value=None, **kwargs):
        self.min_value, self.max_value = min_value, max_value
        models.IntegerField.__init__(self, verbose_name, name, **kwargs)
    def formfield(self, **kwargs):
        defaults = {'min_value': self.min_value, 'max_value':self.max_value}
        defaults.update(kwargs)
        return super(IntegerRangeField, self).formfield(**defaults)

Then in your model class, you would use it like this (field being the module where you put the above code):

size = fields.IntegerRangeField(min_value=1, max_value=50)

OR for a range of negative and positive (like an oscillator range):

size = fields.IntegerRangeField(min_value=-100, max_value=100)

What would be really cool is if it could be called with the range operator like this:

size = fields.IntegerRangeField(range(1, 50))

But, that would require a lot more code since since you can specify a 'skip' parameter - range(1, 50, 2) - Interesting idea though...

User · Answer

from django db import models from django core validators import MinValueValidator  MaxValueValidator  size   models IntegerField validators  MinValueValidator 0                                          MaxValueValidator 5

User · Answer

Here is the best solution if you want some extra flexibility and don t want to change your model field  Just add this custom validator    Imports from django core exceptions import ValidationError        class validate range or null object       compare   lambda self  a  b  c  a  gt  c or a  lt  b     clean   lambda self  x  x     message     Ensure this value is between   limit min s and   limit max s  it is   show value s         code    limit value       def   init   self  limit min  limit max           self limit min   limit min         self limit max   limit max      def   call   self  value           cleaned   self clean value          params     limit min   self limit min   limit max   self limit max   show value   cleaned          if value     make it optional  remove it to make required  or make required on the model             if self compare cleaned  self limit min  self limit max                   raise ValidationError self message  code self code  params params    And it can be used as such   class YourModel models Model                 no dependents   models PositiveSmallIntegerField  How many dependants    blank True  null True  default 0  validators  validate range or null 1 100      The two parameters are max and min  and it allows nulls  You can customize the validator if you like by getting rid of the marked if statement or change your field to be blank False  null False in the model   That will of course require a migration   Note  I had to add the validator because Django does not validate the range on PositiveSmallIntegerField  instead it creates a smallint  in postgres  for this field and you get a DB error if the numeric specified is out of range   Hope this helps    More on Validators in Django   PS  I based my answer on BaseValidator in django core validators  but everything is different except for the code

User · Answer

There are two ways to do this  One is to use form validation to never let any number over 50 be entered by a user  Form validation docs   If there is no user involved in the process  or you re not using a form to enter data  then you ll have to override the model s save method to throw an exception or limit the data going into the field

User · Answer

You can use Django s built-in validators     from django db models import IntegerField  Model from django core validators import MaxValueValidator  MinValueValidator  class CoolModelBro Model       limited integer field   IntegerField          default 1          validators               MaxValueValidator 100               MinValueValidator 1                     Edit  When working directly with the model  make sure to call the model full clean method before saving the model in order to trigger the validators  This is not required when using ModelForm since the forms will do that automatically

User · Answer

I had this very same problem  here was my solution   SCORE CHOICES   zip  range 1 n   range 1 n    score   models IntegerField choices SCORE CHOICES  blank True

[python] How to limit the maximum value of a numeric field in a Django model?

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