Django2.0手册:Form fields



class Field(**kwargs)[source]

When you create a Form class, the most important part is defining the
fields of the form. Each field has custom validation logic, along with a few
other hooks.

Field.clean(value)[source]

Although the primary way you’ll use Field classes is in Form classes,
you can also instantiate them and use them directly to get a better idea of
how they work. Each Field instance has a clean() method, which takes
a single argument and either raises a django.forms.ValidationError
exception or returns the clean value:

>>> from django import forms
>>> f = forms.EmailField()
>>> f.clean('foo@example.com')
'foo@example.com'
>>> f.clean('invalid email address')
Traceback (most recent call last):
...
ValidationError: ['Enter a valid email address.']

Core field arguments¶

Each Field class constructor takes at least these arguments. Some
Field classes take additional, field-specific arguments, but the following
should always be accepted:

required¶

Field.required

By default, each Field class assumes the value is required, so if you pass
an empty value — either None or the empty string ("") — then
clean() will raise a ValidationError exception:

>>> from django import forms
>>> f = forms.CharField()
>>> f.clean('foo')
'foo'
>>> f.clean('')
Traceback (most recent call last):
...
ValidationError: ['This field is required.']
>>> f.clean(None)
Traceback (most recent call last):
...
ValidationError: ['This field is required.']
>>> f.clean(' ')
' '
>>> f.clean(0)
'0'
>>> f.clean(True)
'True'
>>> f.clean(False)
'False'

To specify that a field is not required, pass required=False to the
Field constructor:

>>> f = forms.CharField(required=False)
>>> f.clean('foo')
'foo'
>>> f.clean('')
''
>>> f.clean(None)
''
>>> f.clean(0)
'0'
>>> f.clean(True)
'True'
>>> f.clean(False)
'False'

If a Field has required=False and you pass clean() an empty value,
then clean() will return a normalized empty value rather than raising
ValidationError. For CharField, this will be an empty string. For other
Field classes, it might be None. (This varies from field to field.)

Widgets of required form fields have the required HTML attribute. Set the
Form.use_required_attribute attribute to False to disable it. The
required attribute isn’t included on forms of formsets because the browser
validation may not be correct when adding and deleting formsets.

label¶

Field.label

The label argument lets you specify the “human-friendly” label for this
field. This is used when the Field is displayed in a Form.

As explained in “Outputting forms as HTML” above, the default label for a
Field is generated from the field name by converting all underscores to
spaces and upper-casing the first letter. Specify label if that default
behavior doesn’t result in an adequate label.

Here’s a full example Form that implements label for two of its fields.
We’ve specified auto_id=False to simplify the output:

>>> from django import forms
>>> class CommentForm(forms.Form):
...     name = forms.CharField(label='Your name')
...     url = forms.URLField(label='Your website', required=False)
...     comment = forms.CharField()
>>> f = CommentForm(auto_id=False)
>>> print(f)
<tr><th>Your name:</th><td><input type="text" name="name" required /></td></tr>
<tr><th>Your website:</th><td><input type="url" name="url" /></td></tr>
<tr><th>Comment:</th><td><input type="text" name="comment" required /></td></tr>

label_suffix¶

Field.label_suffix

The label_suffix argument lets you override the form’s
label_suffix on a per-field basis:

>>> class ContactForm(forms.Form):
...     age = forms.IntegerField()
...     nationality = forms.CharField()
...     captcha_answer = forms.IntegerField(label='2 + 2', label_suffix=' =')
>>> f = ContactForm(label_suffix='?')
>>> print(f.as_p())
<p><label for="id_age">Age?</label> <input id="id_age" name="age" type="number" required /></p>
<p><label for="id_nationality">Nationality?</label> <input id="id_nationality" name="nationality" type="text" required /></p>
<p><label for="id_captcha_answer">2 + 2 =</label> <input id="id_captcha_answer" name="captcha_answer" type="number" required /></p>

initial¶

Field.initial

The initial argument lets you specify the initial value to use when
rendering this Field in an unbound Form.

To specify dynamic initial data, see the Form.initial parameter.

The use-case for this is when you want to display an “empty” form in which a
field is initialized to a particular value. For example:

>>> from django import forms
>>> class CommentForm(forms.Form):
...     name = forms.CharField(initial='Your name')
...     url = forms.URLField(initial='http://')
...     comment = forms.CharField()
>>> f = CommentForm(auto_id=False)
>>> print(f)
<tr><th>Name:</th><td><input type="text" name="name" value="Your name" required /></td></tr>
<tr><th>Url:</th><td><input type="url" name="url" value="http://" required /></td></tr>
<tr><th>Comment:</th><td><input type="text" name="comment" required /></td></tr>

You may be thinking, why not just pass a dictionary of the initial values as
data when displaying the form? Well, if you do that, you’ll trigger validation,
and the HTML output will include any validation errors:

>>> class CommentForm(forms.Form):
...     name = forms.CharField()
...     url = forms.URLField()
...     comment = forms.CharField()
>>> default_data = {'name': 'Your name', 'url': 'http://'}
>>> f = CommentForm(default_data, auto_id=False)
>>> print(f)
<tr><th>Name:</th><td><input type="text" name="name" value="Your name" required /></td></tr>
<tr><th>Url:</th><td><ul class="errorlist"><li>Enter a valid URL.</li></ul><input type="url" name="url" value="http://" required /></td></tr>
<tr><th>Comment:</th><td><ul class="errorlist"><li>This field is required.</li></ul><input type="text" name="comment" required /></td></tr>

This is why initial values are only displayed for unbound forms. For bound
forms, the HTML output will use the bound data.

Also note that initial values are not used as “fallback” data in
validation if a particular field’s value is not given. initial values are
only intended for initial form display:

>>> class CommentForm(forms.Form):
...     name = forms.CharField(initial='Your name')
...     url = forms.URLField(initial='http://')
...     comment = forms.CharField()
>>> data = {'name': '', 'url': '', 'comment': 'Foo'}
>>> f = CommentForm(data)
>>> f.is_valid()
False
# The form does *not* fall back to using the initial values.
>>> f.errors
{'url': ['This field is required.'], 'name': ['This field is required.']}

Instead of a constant, you can also pass any callable:

>>> import datetime
>>> class DateForm(forms.Form):
...     day = forms.DateField(initial=datetime.date.today)
>>> print(DateForm())
<tr><th>Day:</th><td><input type="text" name="day" value="12/23/2008" required /><td></tr>

The callable will be evaluated only when the unbound form is displayed, not when it is defined.

widget¶

Field.widget

The widget argument lets you specify a Widget class to use when
rendering this Field. See Widgets for more information.

help_text¶

Field.help_text

The help_text argument lets you specify descriptive text for this
Field. If you provide help_text, it will be displayed next to the
Field when the Field is rendered by one of the convenience Form
methods (e.g., as_ul()).

Like the model field’s help_text, this value
isn’t HTML-escaped in automatically-generated forms.

Here’s a full example Form that implements help_text for two of its
fields. We’ve specified auto_id=False to simplify the output:

>>> from django import forms
>>> class HelpTextContactForm(forms.Form):
...     subject = forms.CharField(max_length=100, help_text='100 characters max.')
...     message = forms.CharField()
...     sender = forms.EmailField(help_text='A valid email address, please.')
...     cc_myself = forms.BooleanField(required=False)
>>> f = HelpTextContactForm(auto_id=False)
>>> print(f.as_table())
<tr><th>Subject:</th><td><input type="text" name="subject" maxlength="100" required /><br /><span class="helptext">100 characters max.</span></td></tr>
<tr><th>Message:</th><td><input type="text" name="message" required /></td></tr>
<tr><th>Sender:</th><td><input type="email" name="sender" required /><br />A valid email address, please.</td></tr>
<tr><th>Cc myself:</th><td><input type="checkbox" name="cc_myself" /></td></tr>
>>> print(f.as_ul()))
<li>Subject: <input type="text" name="subject" maxlength="100" required /> <span class="helptext">100 characters max.</span></li>
<li>Message: <input type="text" name="message" required /></li>
<li>Sender: <input type="email" name="sender" required /> A valid email address, please.</li>
<li>Cc myself: <input type="checkbox" name="cc_myself" /></li>
>>> print(f.as_p())
<p>Subject: <input type="text" name="subject" maxlength="100" required /> <span class="helptext">100 characters max.</span></p>
<p>Message: <input type="text" name="message" required /></p>
<p>Sender: <input type="email" name="sender" required /> A valid email address, please.</p>
<p>Cc myself: <input type="checkbox" name="cc_myself" /></p>

error_messages¶

Field.error_messages

The error_messages argument lets you override the default messages that the
field will raise. Pass in a dictionary with keys matching the error messages you
want to override. For example, here is the default error message:

>>> from django import forms
>>> generic = forms.CharField()
>>> generic.clean('')
Traceback (most recent call last):
  ...
ValidationError: ['This field is required.']

And here is a custom error message:

>>> name = forms.CharField(error_messages={'required': 'Please enter your name'})
>>> name.clean('')
Traceback (most recent call last):
  ...
ValidationError: ['Please enter your name']

In the built-in Field classes section below, each Field defines the
error message keys it uses.

validators¶

Field.validators

The validators argument lets you provide a list of validation functions
for this field.

See the validators documentation for more information.

localize¶

Field.localize

The localize argument enables the localization of form data input, as well
as the rendered output.

See the format localization documentation for
more information.

disabled¶

Field.disabled

The disabled boolean argument, when set to True, disables a form field
using the disabled HTML attribute so that it won’t be editable by users.
Even if a user tampers with the field’s value submitted to the server, it will
be ignored in favor of the value from the form’s initial data.

Checking if the field data has changed¶

has_changed()¶

Field.has_changed()[source]

The has_changed() method is used to determine if the field value has changed
from the initial value. Returns True or False.

See the Form.has_changed() documentation for more information.

Built-in Field classes¶

Naturally, the forms library comes with a set of Field classes that
represent common validation needs. This section documents each built-in field.

For each field, we describe the default widget used if you don’t specify
widget. We also specify the value returned when you provide an empty value
(see the section on required above to understand what that means).

BooleanField¶

class BooleanField(**kwargs)[source]
  • Default widget: CheckboxInput
  • Empty value: False
  • Normalizes to: A Python True or False value.
  • Validates that the value is True (e.g. the check box is checked) if
    the field has required=True.
  • Error message keys: required

Note

Since all Field subclasses have required=True by default, the
validation condition here is important. If you want to include a boolean
in your form that can be either True or False (e.g. a checked or
unchecked checkbox), you must remember to pass in required=False when
creating the BooleanField.

CharField¶

class CharField(**kwargs)[source]
  • Default widget: TextInput
  • Empty value: Whatever you’ve given as empty_value.
  • Normalizes to: A string.
  • Validates max_length or min_length, if they are provided.
    Otherwise, all inputs are valid.
  • Error message keys: required, max_length, min_length

Has three optional arguments for validation:

max_length
min_length

If provided, these arguments ensure that the string is at most or at least
the given length.

strip

If True (default), the value will be stripped of leading and
trailing whitespace.

empty_value
New in Django 1.11.

The value to use to represent “empty”. Defaults to an empty string.

ChoiceField¶

class ChoiceField(**kwargs)[source]
  • Default widget: Select
  • Empty value: '' (an empty string)
  • Normalizes to: A string.
  • Validates that the given value exists in the list of choices.
  • Error message keys: required, invalid_choice

The invalid_choice error message may contain %(value)s, which will be
replaced with the selected choice.

Takes one extra argument:

choices

Either an iterable (e.g., a list or tuple) of 2-tuples to use as
choices for this field, or a callable that returns such an iterable.
This argument accepts the same formats as the choices argument to a
model field. See the model field reference documentation on
choices
for more details. If the argument is a
callable, it is evaluated each time the field’s form is initialized.
Defaults to an empty list.

TypedChoiceField¶

class TypedChoiceField(**kwargs)[source]

Just like a ChoiceField, except TypedChoiceField takes two
extra arguments, coerce and empty_value.

  • Default widget: Select
  • Empty value: Whatever you’ve given as empty_value.
  • Normalizes to: A value of the type provided by the coerce
    argument.
  • Validates that the given value exists in the list of choices and can be
    coerced.
  • Error message keys: required, invalid_choice

Takes extra arguments:

coerce

A function that takes one argument and returns a coerced value. Examples
include the built-in int, float, bool and other types. Defaults
to an identity function. Note that coercion happens after input
validation, so it is possible to coerce to a value not present in
choices.

empty_value

The value to use to represent “empty.” Defaults to the empty string;
None is another common choice here. Note that this value will not be
coerced by the function given in the coerce argument, so choose it
accordingly.

DateField¶

class DateField(**kwargs)[source]
  • Default widget: DateInput
  • Empty value: None
  • Normalizes to: A Python datetime.date object.
  • Validates that the given value is either a datetime.date,
    datetime.datetime or string formatted in a particular date format.
  • Error message keys: required, invalid

Takes one optional argument:

input_formats

A list of formats used to attempt to convert a string to a valid
datetime.date object.

If no input_formats argument is provided, the default input formats are:

['%Y-%m-%d',      # '2006-10-25'
 '%m/%d/%Y',      # '10/25/2006'
 '%m/%d/%y']      # '10/25/06'

Additionally, if you specify USE_L10N=False in your settings, the
following will also be included in the default input formats:

['%b %d %Y',      # 'Oct 25 2006'
 '%b %d, %Y',     # 'Oct 25, 2006'
 '%d %b %Y',      # '25 Oct 2006'
 '%d %b, %Y',     # '25 Oct, 2006'
 '%B %d %Y',      # 'October 25 2006'
 '%B %d, %Y',     # 'October 25, 2006'
 '%d %B %Y',      # '25 October 2006'
 '%d %B, %Y']     # '25 October, 2006'

See also format localization.

DateTimeField¶

class DateTimeField(**kwargs)[source]
  • Default widget: DateTimeInput
  • Empty value: None
  • Normalizes to: A Python datetime.datetime object.
  • Validates that the given value is either a datetime.datetime,
    datetime.date or string formatted in a particular datetime format.
  • Error message keys: required, invalid

Takes one optional argument:

input_formats

A list of formats used to attempt to convert a string to a valid
datetime.datetime object.

If no input_formats argument is provided, the default input formats are:

['%Y-%m-%d %H:%M:%S',    # '2006-10-25 14:30:59'
 '%Y-%m-%d %H:%M',       # '2006-10-25 14:30'
 '%Y-%m-%d',             # '2006-10-25'
 '%m/%d/%Y %H:%M:%S',    # '10/25/2006 14:30:59'
 '%m/%d/%Y %H:%M',       # '10/25/2006 14:30'
 '%m/%d/%Y',             # '10/25/2006'
 '%m/%d/%y %H:%M:%S',    # '10/25/06 14:30:59'
 '%m/%d/%y %H:%M',       # '10/25/06 14:30'
 '%m/%d/%y']             # '10/25/06'

See also format localization.

DecimalField¶

class DecimalField(**kwargs)[source]
  • Default widget: NumberInput when Field.localize is
    False, else TextInput.
  • Empty value: None
  • Normalizes to: A Python decimal.
  • Validates that the given value is a decimal. Leading and trailing
    whitespace is ignored.
  • Error message keys: required, invalid, max_value,
    min_value, max_digits, max_decimal_places,
    max_whole_digits

The max_value and min_value error messages may contain
%(limit_value)s, which will be substituted by the appropriate limit.
Similarly, the max_digits, max_decimal_places and
max_whole_digits error messages may contain %(max)s.

Takes four optional arguments:

max_value
min_value

These control the range of values permitted in the field, and should be
given as decimal.Decimal values.

max_digits

The maximum number of digits (those before the decimal point plus those
after the decimal point, with leading zeros stripped) permitted in the
value.

decimal_places

The maximum number of decimal places permitted.

DurationField¶

class DurationField(**kwargs)[source]
  • Default widget: TextInput
  • Empty value: None
  • Normalizes to: A Python timedelta.
  • Validates that the given value is a string which can be converted into a
    timedelta.
  • Error message keys: required, invalid.

Accepts any format understood by
parse_duration().

EmailField¶

class EmailField(**kwargs)[source]
  • Default widget: EmailInput
  • Empty value: '' (an empty string)
  • Normalizes to: A string.
  • Validates that the given value is a valid email address, using a
    moderately complex regular expression.
  • Error message keys: required, invalid

Has two optional arguments for validation, max_length and min_length.
If provided, these arguments ensure that the string is at most or at least the
given length.

FileField¶

class FileField(**kwargs)[source]
  • Default widget: ClearableFileInput
  • Empty value: None
  • Normalizes to: An UploadedFile object that wraps the file content
    and file name into a single object.
  • Can validate that non-empty file data has been bound to the form.
  • Error message keys: required, invalid, missing, empty,
    max_length

Has two optional arguments for validation, max_length and
allow_empty_file. If provided, these ensure that the file name is at
most the given length, and that validation will succeed even if the file
content is empty.

To learn more about the UploadedFile object, see the file uploads
documentation
.

When you use a FileField in a form, you must also remember to
bind the file data to the form.

The max_length error refers to the length of the filename. In the error
message for that key, %(max)d will be replaced with the maximum filename
length and %(length)d will be replaced with the current filename length.

FilePathField¶

class FilePathField(**kwargs)[source]
  • Default widget: Select
  • Empty value: None
  • Normalizes to: A string.
  • Validates that the selected choice exists in the list of choices.
  • Error message keys: required, invalid_choice

The field allows choosing from files inside a certain directory. It takes five
extra arguments; only path is required:

path

The absolute path to the directory whose contents you want listed. This
directory must exist.

recursive

If False (the default) only the direct contents of path will be
offered as choices. If True, the directory will be descended into
recursively and all descendants will be listed as choices.

match

A regular expression pattern; only files with names matching this expression
will be allowed as choices.

allow_files

Optional. Either True or False. Default is True. Specifies
whether files in the specified location should be included. Either this or
allow_folders must be True.

allow_folders

Optional. Either True or False. Default is False. Specifies
whether folders in the specified location should be included. Either this or
allow_files must be True.

FloatField¶

class FloatField(**kwargs)[source]
  • Default widget: NumberInput when Field.localize is
    False, else TextInput.
  • Empty value: None
  • Normalizes to: A Python float.
  • Validates that the given value is a float. Leading and trailing
    whitespace is allowed, as in Python’s float() function.
  • Error message keys: required, invalid, max_value,
    min_value

Takes two optional arguments for validation, max_value and min_value.
These control the range of values permitted in the field.

ImageField¶

class ImageField(**kwargs)[source]
  • Default widget: ClearableFileInput
  • Empty value: None
  • Normalizes to: An UploadedFile object that wraps the file content
    and file name into a single object.
  • Validates that file data has been bound to the form, and that the
    file is of an image format understood by Pillow.
  • Error message keys: required, invalid, missing, empty,
    invalid_image

Using an ImageField requires that Pillow is installed with support
for the image formats you use. If you encounter a corrupt image error
when you upload an image, it usually means that Pillow doesn’t understand
its format. To fix this, install the appropriate library and reinstall
Pillow.

When you use an ImageField on a form, you must also remember to
bind the file data to the form.

After the field has been cleaned and validated, the UploadedFile
object will have an additional image attribute containing the Pillow
Image instance used to check if the file was a valid image. Also,
UploadedFile.content_type will be updated with the image’s content type
if Pillow can determine it, otherwise it will be set to None.

IntegerField¶

class IntegerField(**kwargs)[source]
  • Default widget: NumberInput when Field.localize is
    False, else TextInput.
  • Empty value: None
  • Normalizes to: A Python integer.
  • Validates that the given value is an integer. Leading and trailing
    whitespace is allowed, as in Python’s int() function.
  • Error message keys: required, invalid, max_value,
    min_value

The max_value and min_value error messages may contain
%(limit_value)s, which will be substituted by the appropriate limit.

Takes two optional arguments for validation:

max_value
min_value

These control the range of values permitted in the field.

GenericIPAddressField¶

class GenericIPAddressField(**kwargs)[source]

A field containing either an IPv4 or an IPv6 address.

  • Default widget: TextInput
  • Empty value: '' (an empty string)
  • Normalizes to: A string. IPv6 addresses are normalized as described below.
  • Validates that the given value is a valid IP address.
  • Error message keys: required, invalid

The IPv6 address normalization follows RFC 4291#section-2.2 section 2.2,
including using the IPv4 format suggested in paragraph 3 of that section, like
::ffff:192.0.2.0. For example, 2001:0::0:01 would be normalized to
2001::1, and ::ffff:0a0a:0a0a to ::ffff:10.10.10.10. All characters
are converted to lowercase.

Takes two optional arguments:

protocol

Limits valid inputs to the specified protocol.
Accepted values are both (default), IPv4
or IPv6. Matching is case insensitive.

unpack_ipv4

Unpacks IPv4 mapped addresses like ::ffff:192.0.2.1.
If this option is enabled that address would be unpacked to
192.0.2.1. Default is disabled. Can only be used
when protocol is set to 'both'.

MultipleChoiceField¶

class MultipleChoiceField(**kwargs)[source]
  • Default widget: SelectMultiple
  • Empty value: [] (an empty list)
  • Normalizes to: A list of strings.
  • Validates that every value in the given list of values exists in the list
    of choices.
  • Error message keys: required, invalid_choice, invalid_list

The invalid_choice error message may contain %(value)s, which will be
replaced with the selected choice.

Takes one extra required argument, choices, as for ChoiceField.

TypedMultipleChoiceField¶

class TypedMultipleChoiceField(**kwargs)[source]

Just like a MultipleChoiceField, except TypedMultipleChoiceField
takes two extra arguments, coerce and empty_value.

  • Default widget: SelectMultiple
  • Empty value: Whatever you’ve given as empty_value
  • Normalizes to: A list of values of the type provided by the coerce
    argument.
  • Validates that the given values exists in the list of choices and can be
    coerced.
  • Error message keys: required, invalid_choice

The invalid_choice error message may contain %(value)s, which will be
replaced with the selected choice.

Takes two extra arguments, coerce and empty_value, as for
TypedChoiceField.

NullBooleanField¶

class NullBooleanField(**kwargs)[source]
  • Default widget: NullBooleanSelect
  • Empty value: None
  • Normalizes to: A Python True, False or None value.
  • Validates nothing (i.e., it never raises a ValidationError).

RegexField¶

class RegexField(**kwargs)[source]
  • Default widget: TextInput
  • Empty value: '' (an empty string)
  • Normalizes to: A string.
  • Validates that the given value matches against a certain regular
    expression.
  • Error message keys: required, invalid

Takes one required argument:

regex

A regular expression specified either as a string or a compiled regular
expression object.

Also takes max_length, min_length, and strip, which work just
as they do for CharField.

strip

Defaults to False. If enabled, stripping will be applied before the
regex validation.

SlugField¶

class SlugField(**kwargs)[source]
  • Default widget: TextInput
  • Empty value: '' (an empty string)
  • Normalizes to: A string.
  • Validates that the given value contains only letters, numbers,
    underscores, and hyphens.
  • Error messages: required, invalid

This field is intended for use in representing a model
SlugField in forms.

Takes an optional parameter:

allow_unicode

A boolean instructing the field to accept Unicode letters in addition
to ASCII letters. Defaults to False.

TimeField¶

class TimeField(**kwargs)[source]
  • Default widget: TextInput
  • Empty value: None
  • Normalizes to: A Python datetime.time object.
  • Validates that the given value is either a datetime.time or string
    formatted in a particular time format.
  • Error message keys: required, invalid

Takes one optional argument:

input_formats

A list of formats used to attempt to convert a string to a valid
datetime.time object.

If no input_formats argument is provided, the default input formats are:

'%H:%M:%S',     # '14:30:59'
'%H:%M',        # '14:30'

URLField¶

class URLField(**kwargs)[source]
  • Default widget: URLInput
  • Empty value: '' (an empty string)
  • Normalizes to: A string.
  • Validates that the given value is a valid URL.
  • Error message keys: required, invalid

Takes the following optional arguments:

max_length
min_length

These are the same as CharField.max_length and CharField.min_length.

UUIDField¶

class UUIDField(**kwargs)[source]
  • Default widget: TextInput
  • Empty value: '' (an empty string)
  • Normalizes to: A UUID object.
  • Error message keys: required, invalid

This field will accept any string format accepted as the hex argument
to the UUID constructor.

Slightly complex built-in Field classes¶

ComboField¶

class ComboField(**kwargs)[source]
  • Default widget: TextInput
  • Empty value: '' (an empty string)
  • Normalizes to: A string.
  • Validates the given value against each of the fields specified
    as an argument to the ComboField.
  • Error message keys: required, invalid

Takes one extra required argument:

fields

The list of fields that should be used to validate the field’s value (in
the order in which they are provided).

>>> from django.forms import ComboField
>>> f = ComboField(fields=[CharField(max_length=20), EmailField()])
>>> f.clean('test@example.com')
'test@example.com'
>>> f.clean('longemailaddress@example.com')
Traceback (most recent call last):
...
ValidationError: ['Ensure this value has at most 20 characters (it has 28).']

MultiValueField¶

class MultiValueField(fields=(), **kwargs)[source]
  • Default widget: TextInput
  • Empty value: '' (an empty string)
  • Normalizes to: the type returned by the compress method of the subclass.
  • Validates the given value against each of the fields specified
    as an argument to the MultiValueField.
  • Error message keys: required, invalid, incomplete

Aggregates the logic of multiple fields that together produce a single
value.

This field is abstract and must be subclassed. In contrast with the
single-value fields, subclasses of MultiValueField must not
implement clean() but instead – implement
compress().

Takes one extra required argument:

fields

A tuple of fields whose values are cleaned and subsequently combined
into a single value. Each value of the field is cleaned by the
corresponding field in fields — the first value is cleaned by the
first field, the second value is cleaned by the second field, etc.
Once all fields are cleaned, the list of clean values is combined into
a single value by compress().

Also takes some optional arguments:

require_all_fields

Defaults to True, in which case a required validation error
will be raised if no value is supplied for any field.

When set to False, the Field.required attribute can be set
to False for individual fields to make them optional. If no value
is supplied for a required field, an incomplete validation error
will be raised.

A default incomplete error message can be defined on the
MultiValueField subclass, or different messages can be defined
on each individual field. For example:

from django.core.validators import RegexValidator

class PhoneField(MultiValueField):
    def __init__(self, **kwargs):
        # Define one message for all fields.
        error_messages = {
            'incomplete': 'Enter a country calling code and a phone number.',
        }
        # Or define a different message for each field.
        fields = (
            CharField(
                error_messages={'incomplete': 'Enter a country calling code.'},
                validators=[
                    RegexValidator(r'^[0-9]+$', 'Enter a valid country calling code.'),
                ],
            ),
            CharField(
                error_messages={'incomplete': 'Enter a phone number.'},
                validators=[RegexValidator(r'^[0-9]+$', 'Enter a valid phone number.')],
            ),
            CharField(
                validators=[RegexValidator(r'^[0-9]+$', 'Enter a valid extension.')],
                required=False,
            ),
        )
        super().__init__(
            error_messages=error_messages, fields=fields,
            require_all_fields=False, **kwargs
        )
widget

Must be a subclass of django.forms.MultiWidget.
Default value is TextInput, which
probably is not very useful in this case.

compress(data_list)[source]

Takes a list of valid values and returns a “compressed” version of
those values — in a single value. For example,
SplitDateTimeField is a subclass which combines a time field
and a date field into a datetime object.

This method must be implemented in the subclasses.

SplitDateTimeField¶

class SplitDateTimeField(**kwargs)[source]
  • Default widget: SplitDateTimeWidget
  • Empty value: None
  • Normalizes to: A Python datetime.datetime object.
  • Validates that the given value is a datetime.datetime or string
    formatted in a particular datetime format.
  • Error message keys: required, invalid, invalid_date,
    invalid_time

Takes two optional arguments:

input_date_formats

A list of formats used to attempt to convert a string to a valid
datetime.date object.

If no input_date_formats argument is provided, the default input formats
for DateField are used.

input_time_formats

A list of formats used to attempt to convert a string to a valid
datetime.time object.

If no input_time_formats argument is provided, the default input formats
for TimeField are used.

Fields which handle relationships¶

Two fields are available for representing relationships between
models: ModelChoiceField and
ModelMultipleChoiceField. Both of these fields require a
single queryset parameter that is used to create the choices for
the field. Upon form validation, these fields will place either one
model object (in the case of ModelChoiceField) or multiple model
objects (in the case of ModelMultipleChoiceField) into the
cleaned_data dictionary of the form.

For more complex uses, you can specify queryset=None when declaring the
form field and then populate the queryset in the form’s __init__()
method:

class FooMultipleChoiceForm(forms.Form):
    foo_select = forms.ModelMultipleChoiceField(queryset=None)

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.fields['foo_select'].queryset = ...

ModelChoiceField¶

class ModelChoiceField(**kwargs)[source]
  • Default widget: Select
  • Empty value: None
  • Normalizes to: A model instance.
  • Validates that the given id exists in the queryset.
  • Error message keys: required, invalid_choice

Allows the selection of a single model object, suitable for representing a
foreign key. Note that the default widget for ModelChoiceField becomes
impractical when the number of entries increases. You should avoid using it
for more than 100 items.

A single argument is required:

queryset

A QuerySet of model objects from which the choices for the field
are derived and which is used to validate the user’s selection. It’s
evaluated when the form is rendered.

ModelChoiceField also takes two optional arguments:

empty_label

By default the <select> widget used by ModelChoiceField will have an
empty choice at the top of the list. You can change the text of this
label (which is "---------" by default) with the empty_label
attribute, or you can disable the empty label entirely by setting
empty_label to None:

# A custom empty label
field1 = forms.ModelChoiceField(queryset=..., empty_label="(Nothing)")

# No empty label
field2 = forms.ModelChoiceField(queryset=..., empty_label=None)

Note that if a ModelChoiceField is required and has a default
initial value, no empty choice is created (regardless of the value
of empty_label).

to_field_name

This optional argument is used to specify the field to use as the value
of the choices in the field’s widget. Be sure it’s a unique field for
the model, otherwise the selected value could match more than one
object. By default it is set to None, in which case the primary key
of each object will be used. For example:

# No custom to_field_name
field1 = forms.ModelChoiceField(queryset=...)

would yield:

<select id="id_field1" name="field1">
<option value="obj1.pk">Object1</option>
<option value="obj2.pk">Object2</option>
...
</select>

and:

# to_field_name provided
field2 = forms.ModelChoiceField(queryset=..., to_field_name="name")

would yield:

<select id="id_field2" name="field2">
<option value="obj1.name">Object1</option>
<option value="obj2.name">Object2</option>
...
</select>

The __str__() method of the model will be called to generate string
representations of the objects for use in the field’s choices. To provide
customized representations, subclass ModelChoiceField and override
label_from_instance. This method will receive a model object and should
return a string suitable for representing it. For example:

from django.forms import ModelChoiceField

class MyModelChoiceField(ModelChoiceField):
    def label_from_instance(self, obj):
        return "My Object #%i" % obj.id

ModelMultipleChoiceField¶

class ModelMultipleChoiceField(**kwargs)[source]
  • Default widget: SelectMultiple
  • Empty value: An empty QuerySet (self.queryset.none())
  • Normalizes to: A QuerySet of model instances.
  • Validates that every id in the given list of values exists in the
    queryset.
  • Error message keys: required, list, invalid_choice,
    invalid_pk_value

The invalid_choice message may contain %(value)s and the
invalid_pk_value message may contain %(pk)s, which will be
substituted by the appropriate values.

Allows the selection of one or more model objects, suitable for
representing a many-to-many relation. As with ModelChoiceField,
you can use label_from_instance to customize the object
representations.

A single argument is required:

queryset

Same as ModelChoiceField.queryset.

Takes one optional argument:

to_field_name

Same as ModelChoiceField.to_field_name.

Creating custom fields¶

If the built-in Field classes don’t meet your needs, you can easily create
custom Field classes. To do this, just create a subclass of
django.forms.Field. Its only requirements are that it implement a
clean() method and that its __init__() method accept the core arguments
mentioned above (required, label, initial, widget,
help_text).

You can also customize how a field will be accessed by overriding
get_bound_field().