[1.2.X] Fixed #14537 -- Added documentation on where validators can be...

==================

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.

:exc:`~django.core.exceptions.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::

        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``

You can add this to a model field via the field's :attr:`~django.db.models.Field.validators`

argument::

    from django.db import models

how validators are run in forms, and :ref:`Validating objects

<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 :doc:`ModelForm documentation </topics/forms/modelforms>`

for information on how model validation interacts with forms.

:class:`~django.forms.ModelForm`, it will run your validators on any fields

that are included in your form. See the

:doc:`ModelForm documentation </topics/forms/modelforms>` for information on

how model validation interacts with forms.

Built-in validators

===================

Django has 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 :mod:`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)

.. class:: RegexValidator(regex, [message=None, code=None])

    .. attribute:: 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.

        or a pre-compiled regular expression. Raises a

        :exc:`~django.core.exceptions.ValidationError` with :attr:`.message`

        and :attr:`.code` if no match is found.

.. attribute:: message=None

    .. attribute:: message

The error message used by ``ValidationError`` if validation fails. If no

``message`` is specified, a generic ``"Enter a valid value"`` message is used.

        The error message used by :exc:`~django.core.exceptions.ValidationError`

        if validation fails. If no :attr:`.message` is specified, a generic

        ``"Enter a valid value"`` message is used. Default value: ``None``.

.. attribute:: code=None

    .. attribute:: code

The error code used by ``ValidationError`` if validation fails. If ``code``

is not specified, ``"invalid"`` is used.

        The error code used by :exc:`~django.core.exceptions.ValidationError`

        if validation fails. If :attr:`.code` is not specified, ``"invalid"``

        is used. Default value: ``None``.

``URLValidator``

----------------

.. class:: URLValidator([verify_exists=False, validator_user_agent=URL_VALIDATOR_USER_AGENT])

.. 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.

    A :class:`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.

.. attribute:: verify_exists=False

    .. attribute:: verify_exists

If ``verify_exists`` is ``True``, this validator checks that the URL actually

exists.

        Default value: ``False``. If set to ``True``, this validator checks

        that the URL actually exists.

.. attribute:: validator_user_agent=URL_VALIDATOR_USER_AGENT

    .. attribute:: validator_user_agent

If ``verify_exists`` is ``True``, it uses ``validator_user_agent`` as the "User-agent"

for the request. This defaults to ``settings.URL_VALIDATOR_USER_AGENT``.

        If :attr:`.verify_exists` is ``True``, Django uses the value of

        :attr:`.validator_user_agent` as the "User-agent" for the request. This

        defaults to :setting:`settings.URL_VALIDATOR_USER_AGENT <URL_VALIDATOR_USER_AGENT>`.

``validate_email``

------------------

.. data:: validate_email

A ``RegexValidator`` instance that ensures a value looks like an e-mail address.

    A :class:`RegexValidator` instance that ensures a value looks like an

    e-mail address.

``validate_slug``

-----------------

.. data:: validate_slug

A ``RegexValidator`` instance that ensures a value consists of only letters,

numbers, underscores or hyphens.

    A :class:`RegexValidator` instance that ensures a value consists of only

    letters, numbers, underscores or hyphens.

``validate_ipv4_address``

-------------------------

.. data:: validate_ipv4_address

A ``RegexValidator`` instance that ensures a value looks like an IPv4 address.

    A :class:`RegexValidator` instance that ensures a value looks like an IPv4

    address.

``validate_comma_separated_integer_list``

-----------------------------------------

.. data:: validate_comma_separated_integer_list

A ``RegexValidator`` instance that ensures a value is a comma-separated list

of integers.

    A :class:`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``.

    Raises a :exc:`~django.core.exceptions.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``.

    Raises a :exc:`~django.core.exceptions.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``.

    Raises a :exc:`~django.core.exceptions.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``.

    Raises a :exc:`~django.core.exceptions.ValidationError` with a code of

    ``'min_length'`` if the length of ``value`` is less than ``min_length``.

Creating forms from models

==========================

.. module:: django.forms.models

   :synopsis: ModelForm and ModelFormset.

.. currentmodule:: django.forms

``ModelForm``

=============

.. class:: ModelForm

If you're building a database-driven app, chances are you'll have forms that

map closely to Django models. For instance, you might have a ``BlogComment``