A validator is a callable that takes a value and raises a ValidationError if it doesn’t meet some criteria. Validators can be useful for re-using validation logic between different types of fields.
For example, here’s a validator that only allows even numbers:
from django.core.exceptions import ValidationError def validate_even(value): if value % 2 != 0: raise ValidationError(u'%s is not an even number' % value)
You can add this to a model field via the field’s validators argument:
from django.db import models class MyModel(models.Model): even_field = models.IntegerField(validators=[validate_even])
Because values are converted to Python before validators are run, you can even use the same validator with forms:
from django import forms class MyForm(forms.Form): even_field = forms.IntegerField(validators=[validate_even])
See the form validation for more information on how validators are run in forms, and Validating objects for how they’re run in models. Note that validators will not be run automatically when you save a model, but if you are using a ModelForm, it will run your validators on any fields that are included in your form. See the ModelForm documentation for information on how model validation interacts with forms.
The django.core.validators module contains a collection of callable validators for use with model and form fields. They’re used internally but are available for use with your own fields, too. They can be used in addition to, or in lieu of custom field.clean() methods.
The regular expression pattern to search for the provided value, or a pre-compiled regular expression. Raises a ValidationError with message and code if no match is found. By default, matches any string (including an empty string).
The error message used by ValidationError if validation fails. Defaults to "Enter a valid value".
An EmailValidator instance that ensures a value looks like an email address.
Uses django.utils.ipv6 to check the validity of an IPv6 address.
Uses both validate_ipv4_address and validate_ipv6_address to ensure a value is either a valid IPv4 or IPv6 address.