Model field reference¶
This document contains all the gory details about all the field options and field types Django’s got to offer.
See also
If the built-in fields don’t do the trick, you can try
django.contrib.localflavor
, which contains assorted pieces of code
that are useful for particular countries or cultures. Also, you can easily
write your own custom model fields.
Note
Technically, these models are defined in django.db.models.fields
, but
for convenience they’re imported into django.db.models
; the standard
convention is to use from django.db import models
and refer to fields as
models.<Foo>Field
.
Field options¶
The following arguments are available to all field types. All are optional.
null
¶
-
Field.
null
¶
If True
, Django will store empty values as NULL
in the database. Default
is False
.
Note that empty string values will always get stored as empty strings, not as
NULL
. Only use null=True
for non-string fields such as integers,
booleans and dates. For both types of fields, you will also need to set
blank=True
if you wish to permit empty values in forms, as the
null
parameter only affects database storage (see
blank
).
Avoid using null
on string-based fields such as
CharField
and TextField
unless you have an excellent reason.
If a string-based field has null=True
, that means it has two possible values
for “no data”: NULL
, and the empty string. In most cases, it’s redundant to
have two possible values for “no data;” Django convention is to use the empty
string, not NULL
.
Note
When using the Oracle database backend, the value NULL
will be stored to
denote the empty string regardless of this attribute.
If you want to accept null
values with BooleanField
,
use NullBooleanField
instead.
blank
¶
-
Field.
blank
¶
If True
, the field is allowed to be blank. Default is False
.
Note that this is different than null
. null
is
purely database-related, whereas blank
is validation-related. If
a field has blank=True
, form validation will allow entry of an empty value.
If a field has blank=False
, the field will be required.
choices
¶
-
Field.
choices
¶
An iterable (e.g., a list or tuple) of 2-tuples to use as choices for this field. If this is given, the default form widget will be a select box with these choices instead of the standard text field.
The first element in each tuple is the actual value to be stored, and the second element is the human-readable name. For example:
YEAR_IN_SCHOOL_CHOICES = (
('FR', 'Freshman'),
('SO', 'Sophomore'),
('JR', 'Junior'),
('SR', 'Senior'),
)
Generally, it’s best to define choices inside a model class, and to define a suitably-named constant for each value:
class Student(models.Model):
FRESHMAN = 'FR'
SOPHOMORE = 'SO'
JUNIOR = 'JR'
SENIOR = 'SR'
YEAR_IN_SCHOOL_CHOICES = (
(FRESHMAN, 'Freshman'),
(SOPHOMORE, 'Sophomore'),
(JUNIOR, 'Junior'),
(SENIOR, 'Senior'),
)
year_in_school = models.CharField(max_length=2,
choices=YEAR_IN_SCHOOL_CHOICES,
default=FRESHMAN)
def is_upperclass(self):
return self.year_in_school in (self.JUNIOR, self.SENIOR)
Though you can define a choices list outside of a model class and then
refer to it, defining the choices and names for each choice inside the
model class keeps all of that information with the class that uses it,
and makes the choices easy to reference (e.g, Student.SOPHOMORE
will work anywhere that the Student
model has been imported).
You can also collect your available choices into named groups that can be used for organizational purposes:
MEDIA_CHOICES = (
('Audio', (
('vinyl', 'Vinyl'),
('cd', 'CD'),
)
),
('Video', (
('vhs', 'VHS Tape'),
('dvd', 'DVD'),
)
),
('unknown', 'Unknown'),
)
The first element in each tuple is the name to apply to the group. The second element is an iterable of 2-tuples, with each 2-tuple containing a value and a human-readable name for an option. Grouped options may be combined with ungrouped options within a single list (such as the unknown option in this example).
For each model field that has choices
set, Django will add a
method to retrieve the human-readable name for the field’s current value. See
get_FOO_display()
in the database API
documentation.
Finally, note that choices can be any iterable object – not necessarily a list
or tuple. This lets you construct choices dynamically. But if you find yourself
hacking choices
to be dynamic, you’re probably better off using a
proper database table with a ForeignKey
. choices
is
meant for static data that doesn’t change much, if ever.
db_column
¶
-
Field.
db_column
¶
The name of the database column to use for this field. If this isn’t given, Django will use the field’s name.
If your database column name is an SQL reserved word, or contains characters that aren’t allowed in Python variable names – notably, the hyphen – that’s OK. Django quotes column and table names behind the scenes.
db_index
¶
-
Field.
db_index
¶
If True
, django-admin.py sqlindexes
will output a
CREATE INDEX
statement for this field.
db_tablespace
¶
-
Field.
db_tablespace
¶
The name of the database tablespace to use for
this field’s index, if this field is indexed. The default is the project’s
DEFAULT_INDEX_TABLESPACE
setting, if set, or the
db_tablespace
of the model, if any. If the backend doesn’t
support tablespaces for indexes, this option is ignored.
default
¶
-
Field.
default
¶
The default value for the field. This can be a value or a callable object. If callable it will be called every time a new object is created.
The default cannot be a mutable object (model instance, list, set, etc.), as a
reference to the same instance of that object would be used as the default
value in all new model instances. Instead, wrap the desired default in a
callable. For example, if you had a custom JSONField
and wanted to specify
a dictionary as the default, use a lambda
as follows:
contact_info = JSONField("ContactInfo", default=lambda:{"email": "to1@example.com"})
editable
¶
-
Field.
editable
¶
If False
, the field will not be displayed in the admin or any other
ModelForm
. Default is True
.
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.
Error message keys include null
, blank
, invalid
, invalid_choice
,
and unique
. Additional error message keys are specified for each field in
the Field types section below.
help_text
¶
-
Field.
help_text
¶
Extra “help” text to be displayed with the form widget. It’s useful for documentation even if your field isn’t used on a form.
Note that this value is not HTML-escaped in automatically-generated
forms. This lets you include HTML in help_text
if you so
desire. For example:
help_text="Please use the following format: <em>YYYY-MM-DD</em>."
Alternatively you can use plain text and
django.utils.html.escape()
to escape any HTML special characters.
primary_key
¶
-
Field.
primary_key
¶
If True
, this field is the primary key for the model.
If you don’t specify primary_key=True
for any field in your model, Django
will automatically add an AutoField
to hold the primary key, so you
don’t need to set primary_key=True
on any of your fields unless you want to
override the default primary-key behavior. For more, see
自增主键字段.
primary_key=True
implies null=False
and unique=True
.
Only one primary key is allowed on an object.
unique
¶
-
Field.
unique
¶
If True
, this field must be unique throughout the table.
This is enforced at the database level and by model validation. If
you try to save a model with a duplicate value in a unique
field, a django.db.IntegrityError
will be raised by the model’s
save()
method.
This option is valid on all field types except ManyToManyField
and
FileField
.
Note that when unique
is True
, you don’t need to specify
db_index
, because unique
implies the creation of an index.
unique_for_date
¶
-
Field.
unique_for_date
¶
Set this to the name of a DateField
or DateTimeField
to
require that this field be unique for the value of the date field.
For example, if you have a field title
that has
unique_for_date="pub_date"
, then Django wouldn’t allow the entry of two
records with the same title
and pub_date
.
This is enforced by model validation but not at the database level.
unique_for_month
¶
-
Field.
unique_for_month
¶
Like unique_for_date
, but requires the field to be unique with
respect to the month.
verbose_name
¶
-
Field.
verbose_name
¶
A human-readable name for the field. If the verbose name isn’t given, Django will automatically create it using the field’s attribute name, converting underscores to spaces. See Verbose field names.
validators
¶
-
Field.
validators
¶
A list of validators to run for this field. See the validators documentation for more information.
Field types¶
AutoField
¶
-
class
AutoField
(**options)¶
An IntegerField
that automatically increments
according to available IDs. You usually won’t need to use this directly; a
primary key field will automatically be added to your model if you don’t specify
otherwise. See 自增主键字段.
BigIntegerField
¶
-
class
BigIntegerField
([**options])¶
A 64 bit integer, much like an IntegerField
except that it is
guaranteed to fit numbers from -9223372036854775808 to 9223372036854775807. The
default form widget for this field is a TextInput
.
BooleanField
¶
-
class
BooleanField
(**options)¶
A true/false field.
The default form widget for this field is a
CheckboxInput
.
If you need to accept null
values then use
NullBooleanField
instead.
CharField
¶
-
class
CharField
(max_length=None[, **options])¶
A string field, for small- to large-sized strings.
For large amounts of text, use TextField
.
The default form widget for this field is a TextInput
.
CharField
has one extra required argument:
-
CharField.
max_length
¶ The maximum length (in characters) of the field. The max_length is enforced at the database level and in Django’s validation.
Note
If you are writing an application that must be portable to multiple
database backends, you should be aware that there are restrictions on
max_length
for some backends. Refer to the database backend
notes for details.
MySQL users
If you are using this field with MySQLdb 1.2.2 and the utf8_bin
collation (which is not the default), there are some issues to be aware
of. Refer to the MySQL database notes for
details.
CommaSeparatedIntegerField
¶
-
class
CommaSeparatedIntegerField
(max_length=None[, **options])¶
A field of integers separated by commas. As in CharField
, the
max_length
argument is required and the note about database
portability mentioned there should be heeded.
DateField
¶
-
class
DateField
([auto_now=False, auto_now_add=False, **options])¶
A date, represented in Python by a datetime.date
instance. Has a few extra,
optional arguments:
-
DateField.
auto_now
¶ Automatically set the field to now every time the object is saved. Useful for “last-modified” timestamps. Note that the current date is always used; it’s not just a default value that you can override.
-
DateField.
auto_now_add
¶ Automatically set the field to now when the object is first created. Useful for creation of timestamps. Note that the current date is always used; it’s not just a default value that you can override.
The default form widget for this field is a
TextInput
. The admin adds a JavaScript calendar,
and a shortcut for “Today”. Includes an additional invalid_date
error
message key.
Note
As currently implemented, setting auto_now
or auto_now_add
to
True
will cause the field to have editable=False
and blank=True
set.
DateTimeField
¶
-
class
DateTimeField
([auto_now=False, auto_now_add=False, **options])¶
A date and time, represented in Python by a datetime.datetime
instance.
Takes the same extra arguments as DateField
.
The default form widget for this field is a single
TextInput
. The admin uses two separate
TextInput
widgets with JavaScript shortcuts.
DecimalField
¶
-
class
DecimalField
(max_digits=None, decimal_places=None[, **options])¶
A fixed-precision decimal number, represented in Python by a
Decimal
instance. Has two required arguments:
-
DecimalField.
max_digits
¶ The maximum number of digits allowed in the number. Note that this number must be greater than or equal to
decimal_places
, if it exists.
-
DecimalField.
decimal_places
¶ The number of decimal places to store with the number.
For example, to store numbers up to 999 with a resolution of 2 decimal places, you’d use:
models.DecimalField(..., max_digits=5, decimal_places=2)
And to store numbers up to approximately one billion with a resolution of 10 decimal places:
models.DecimalField(..., max_digits=19, decimal_places=10)
The default form widget for this field is a TextInput
.
Note
For more information about the differences between the
FloatField
and DecimalField
classes, please
see FloatField vs. DecimalField.
EmailField
¶
-
class
EmailField
([max_length=75, **options])¶
A CharField
that checks that the value is a valid email address.
Incompliance to RFCs
The default 75 character max_length
is not capable of storing all
possible RFC3696/5321-compliant email addresses. In order to store all
possible valid email addresses, a max_length
of 254 is required.
The default max_length
of 75 exists for historical reasons. The
default has not been changed in order to maintain backwards
compatibility with existing uses of EmailField
.
FileField
¶
-
class
FileField
(upload_to=None[, max_length=100, **options])¶
A file-upload field.
Note
The primary_key
and unique
arguments are not supported, and will
raise a TypeError
if used.
Has one required argument:
-
FileField.
upload_to
¶ A local filesystem path that will be appended to your
MEDIA_ROOT
setting to determine the value of theurl
attribute.This path may contain
strftime()
formatting, which will be replaced by the date/time of the file upload (so that uploaded files don’t fill up the given directory).This may also be a callable, such as a function, which will be called to obtain the upload path, including the filename. This callable must be able to accept two arguments, and return a Unix-style path (with forward slashes) to be passed along to the storage system. The two arguments that will be passed are:
Argument Description instance
An instance of the model where the
FileField
is defined. More specifically, this is the particular instance where the current file is being attached.In most cases, this object will not have been saved to the database yet, so if it uses the default
AutoField
, it might not yet have a value for its primary key field.filename
The filename that was originally given to the file. This may or may not be taken into account when determining the final destination path.
Also has one optional argument:
-
FileField.
storage
¶ Optional. A storage object, which handles the storage and retrieval of your files. See Managing files for details on how to provide this object.
The default form widget for this field is a FileInput
.
Using a FileField
or an ImageField
(see below) in a model
takes a few steps:
- In your settings file, you’ll need to define
MEDIA_ROOT
as the full path to a directory where you’d like Django to store uploaded files. (For performance, these files are not stored in the database.) DefineMEDIA_URL
as the base public URL of that directory. Make sure that this directory is writable by the Web server’s user account. - Add the
FileField
orImageField
to your model, making sure to define theupload_to
option to tell Django to which subdirectory ofMEDIA_ROOT
it should upload files. - All that will be stored in your database is a path to the file
(relative to
MEDIA_ROOT
). You’ll most likely want to use the convenienceurl
attribute provided by Django. For example, if yourImageField
is calledmug_shot
, you can get the absolute path to your image in a template with{{ object.mug_shot.url }}
.
For example, say your MEDIA_ROOT
is set to '/home/media'
, and
upload_to
is set to 'photos/%Y/%m/%d'
. The '%Y/%m/%d'
part of upload_to
is strftime()
formatting;
'%Y'
is the four-digit year, '%m'
is the two-digit month and '%d'
is
the two-digit day. If you upload a file on Jan. 15, 2007, it will be saved in
the directory /home/media/photos/2007/01/15
.
If you wanted to retrieve the uploaded file’s on-disk filename, or the file’s
size, you could use the name
and
size
attributes respectively; for more
information on the available attributes and methods, see the
File
class reference and the Managing files
topic guide.
Note
The file is saved as part of saving the model in the database, so the actual file name used on disk cannot be relied on until after the model has been saved.
The uploaded file’s relative URL can be obtained using the
url
attribute. Internally,
this calls the url()
method of the
underlying Storage
class.
Note that whenever you deal with uploaded files, you should pay close attention to where you’re uploading them and what type of files they are, to avoid security holes. Validate all uploaded files so that you’re sure the files are what you think they are. For example, if you blindly let somebody upload files, without validation, to a directory that’s within your Web server’s document root, then somebody could upload a CGI or PHP script and execute that script by visiting its URL on your site. Don’t allow that.
Also note that even an uploaded HTML file, since it can be executed by the browser (though not by the server), can pose security threats that are equivalent to XSS or CSRF attacks.
By default, FileField
instances are
created as varchar(100)
columns in your database. As with other fields, you
can change the maximum length using the max_length
argument.
FileField and FieldFile¶
-
class
FieldFile
¶
When you access a FileField
on a model, you are
given an instance of FieldFile
as a proxy for accessing the underlying
file. This class has several attributes and methods that can be used to
interact with file data:
-
FieldFile.
url
¶
A read-only property to access the file’s relative URL by calling the
url()
method of the underlying
Storage
class.
-
FieldFile.
open
(mode='rb')¶
Behaves like the standard Python open()
method and opens the file
associated with this instance in the mode specified by mode
.
-
FieldFile.
close
()¶
Behaves like the standard Python file.close()
method and closes the file
associated with this instance.
-
FieldFile.
save
(name, content, save=True)¶
This method takes a filename and file contents and passes them to the storage
class for the field, then associates the stored file with the model field.
If you want to manually associate file data with
FileField
instances on your model, the save()
method is used to persist that file data.
Takes two required arguments: name
which is the name of the file, and
content
which is an object containing the file’s contents. The
optional save
argument controls whether or not the instance is
saved after the file has been altered. Defaults to True
.
Note that the content
argument should be an instance of
django.core.files.File
, not Python’s built-in file object.
You can construct a File
from an existing
Python file object like this:
from django.core.files import File
# Open an existing file using Python's built-in open()
f = open('/tmp/hello.world')
myfile = File(f)
Or you can construct one from a Python string like this:
from django.core.files.base import ContentFile
myfile = ContentFile("hello world")
For more information, see Managing files.
-
FieldFile.
delete
(save=True)¶
Deletes the file associated with this instance and clears all attributes on
the field. Note: This method will close the file if it happens to be open when
delete()
is called.
The optional save
argument controls whether or not the instance is saved
after the file has been deleted. Defaults to True
.
Note that when a model is deleted, related files are not deleted. If you need to cleanup orphaned files, you’ll need to handle it yourself (for instance, with a custom management command that can be run manually or scheduled to run periodically via e.g. cron).
FilePathField
¶
-
class
FilePathField
(path=None[, match=None, recursive=False, max_length=100, **options])¶
A CharField
whose choices are limited to the filenames in a certain
directory on the filesystem. Has three special arguments, of which the first is
required:
-
FilePathField.
path
¶ Required. The absolute filesystem path to a directory from which this
FilePathField
should get its choices. Example:"/home/images"
.
-
FilePathField.
match
¶ Optional. A regular expression, as a string, that
FilePathField
will use to filter filenames. Note that the regex will be applied to the base filename, not the full path. Example:"foo.*\.txt$"
, which will match a file calledfoo23.txt
but notbar.txt
orfoo23.png
.
-
FilePathField.
recursive
¶ Optional. Either
True
orFalse
. Default isFalse
. Specifies whether all subdirectories ofpath
should be included
-
FilePathField.
allow_files
¶ Optional. Either
True
orFalse
. Default isTrue
. Specifies whether files in the specified location should be included. Either this orallow_folders
must beTrue
.
-
FilePathField.
allow_folders
¶ Optional. Either
True
orFalse
. Default isFalse
. Specifies whether folders in the specified location should be included. Either this orallow_files
must beTrue
.
Of course, these arguments can be used together.
The one potential gotcha is that match
applies to the
base filename, not the full path. So, this example:
FilePathField(path="/home/images", match="foo.*", recursive=True)
...will match /home/images/foo.png
but not /home/images/foo/bar.png
because the match
applies to the base filename
(foo.png
and bar.png
).
By default, FilePathField
instances are
created as varchar(100)
columns in your database. As with other fields, you
can change the maximum length using the max_length
argument.
FloatField
¶
-
class
FloatField
([**options])¶
A floating-point number represented in Python by a float
instance.
The default form widget for this field is a TextInput
.
FloatField
vs. DecimalField
The FloatField
class is sometimes mixed up with the
DecimalField
class. Although they both represent real numbers, they
represent those numbers differently. FloatField
uses Python’s float
type internally, while DecimalField
uses Python’s Decimal
type. For
information on the difference between the two, see Python’s documentation
for the decimal
module.
ImageField
¶
-
class
ImageField
(upload_to=None[, height_field=None, width_field=None, max_length=100, **options])¶
Inherits all attributes and methods from FileField
, but also
validates that the uploaded object is a valid image.
In addition to the special attributes that are available for FileField
,
an ImageField
also has height
and width
attributes.
To facilitate querying on those attributes, ImageField
has two extra
optional arguments:
-
ImageField.
height_field
¶ Name of a model field which will be auto-populated with the height of the image each time the model instance is saved.
-
ImageField.
width_field
¶ Name of a model field which will be auto-populated with the width of the image each time the model instance is saved.
Requires the Python Imaging Library.
By default, ImageField
instances are created as varchar(100)
columns in your database. As with other fields, you can change the maximum
length using the max_length
argument.
IntegerField
¶
-
class
IntegerField
([**options])¶
An integer. The default form widget for this field is a
TextInput
.
IPAddressField
¶
-
class
IPAddressField
([**options])¶
An IP address, in string format (e.g. “192.0.2.30”). The default form widget
for this field is a TextInput
.
GenericIPAddressField
¶
-
class
GenericIPAddressField
([protocol=both, unpack_ipv4=False, **options])¶
An IPv4 or IPv6 address, in string format (e.g. 192.0.2.30
or
2a02:42fe::4
). The default form widget for this field is a
TextInput
.
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.
-
GenericIPAddressField.
protocol
¶ Limits valid inputs to the specified protocol. Accepted values are
'both'
(default),'IPv4'
or'IPv6'
. Matching is case insensitive.
-
GenericIPAddressField.
unpack_ipv4
¶ Unpacks IPv4 mapped addresses like
::ffff:192.0.2.1
. If this option is enabled that address would be unpacked to192.0.2.1
. Default is disabled. Can only be used whenprotocol
is set to'both'
.
NullBooleanField
¶
-
class
NullBooleanField
([**options])¶
Like a BooleanField
, but allows NULL
as one of the options. Use
this instead of a BooleanField
with null=True
. The default form
widget for this field is a NullBooleanSelect
.
PositiveIntegerField
¶
-
class
PositiveIntegerField
([**options])¶
Like an IntegerField
, but must be either positive or zero (0).
The value 0 is accepted for backward compatibility reasons.
PositiveSmallIntegerField
¶
-
class
PositiveSmallIntegerField
([**options])¶
Like a PositiveIntegerField
, but only allows values under a certain
(database-dependent) point.
SlugField
¶
-
class
SlugField
([max_length=50, **options])¶
Slug is a newspaper term. A slug is a short label for something, containing only letters, numbers, underscores or hyphens. They’re generally used in URLs.
Like a CharField, you can specify max_length
(read the note
about database portability and max_length
in that section,
too). If max_length
is not specified, Django will use a
default length of 50.
Implies setting Field.db_index
to True
.
It is often useful to automatically prepopulate a SlugField based on the value
of some other value. You can do this automatically in the admin using
prepopulated_fields
.
SmallIntegerField
¶
-
class
SmallIntegerField
([**options])¶
Like an IntegerField
, but only allows values under a certain
(database-dependent) point.
TextField
¶
-
class
TextField
([**options])¶
A large text field. The default form widget for this field is a
Textarea
.
MySQL users
If you are using this field with MySQLdb 1.2.1p2 and the utf8_bin
collation (which is not the default), there are some issues to be aware
of. Refer to the MySQL database notes for
details.
TimeField
¶
-
class
TimeField
([auto_now=False, auto_now_add=False, **options])¶
A time, represented in Python by a datetime.time
instance. Accepts the same
auto-population options as DateField
.
The default form widget for this field is a TextInput
.
The admin adds some JavaScript shortcuts.
URLField
¶
-
class
URLField
([max_length=200, **options])¶
A CharField
for a URL.
The default form widget for this field is a TextInput
.
Like all CharField
subclasses, URLField
takes the optional
max_length
argument. If you don’t specify
max_length
, a default of 200 is used.
The current value of the field will be displayed as a clickable link above the input widget.