Writing validators
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])
How validators are run
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.
Built-in validators
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.
RegexValidator
-
class RegexValidator(regex[, message=None, code=None])
-
regex
- 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.
-
message
- The error message used by ValidationError
if validation fails. If no message is specified, a generic
"Enter a valid value" message is used. Default value: None.
-
code
- The error code used by ValidationError
if validation fails. If code is not specified, "invalid"
is used. Default value: None.
URLValidator
-
class URLValidator([verify_exists=False, validator_user_agent=URL_VALIDATOR_USER_AGENT])
A RegexValidator that ensures a value looks like a URL and
optionally verifies that the URL actually exists (i.e., doesn't return a
404 status code). Raises an error code of 'invalid' if it doesn't look
like a URL, and a code of 'invalid_link' if it doesn't exist.
-
verify_exists
- Default value: False. If set to True, this validator checks
that the URL actually exists.
-
validator_user_agent
- If verify_exists is True, Django uses the value of
validator_user_agent as the "User-agent" for the request. This
defaults to settings.URL_VALIDATOR_USER_AGENT.
validate_email
-
validate_email
- A RegexValidator instance that ensures a value looks like an
e-mail address.
validate_slug
-
validate_slug
- A RegexValidator instance that ensures a value consists of only
letters, numbers, underscores or hyphens.
validate_ipv4_address
-
validate_ipv4_address
- A RegexValidator instance that ensures a value looks like an IPv4
address.
validate_comma_separated_integer_list
-
validate_comma_separated_integer_list
- A RegexValidator instance that ensures a value is a
comma-separated list of integers.
MaxValueValidator
-
class MaxValueValidator(max_value)
- Raises a ValidationError with a code of
'max_value' if value is greater than max_value.
MinValueValidator
-
class MinValueValidator(min_value)
- Raises a ValidationError with a code of
'min_value' if value is less than min_value.
MaxLengthValidator
-
class MaxLengthValidator(max_length)
- Raises a ValidationError with a code of
'max_length' if the length of value is greater than max_length.
MinLengthValidator
-
class MinLengthValidator(min_length)
- Raises a ValidationError with a code of
'min_length' if the length of value is less than min_length.