- Language: en
Model field reference¶
This document contains all the API references of Field
including the
field options and field types Django offers.
See also
If the built-in fields don’t do the trick, you can try django-localflavor (documentation), which contains assorted pieces of code that are useful for particular countries and cultures.
Also, you can easily write your own custom model fields.
Note
Fields 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
.
Avoid using null
on string-based fields such as
CharField
and TextField
. The Django convention is to use an
empty string, not NULL
, as the “no data” state for string-based fields. If a
string-based field has null=False
, empty strings can still be saved for “no
data”. 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”. One exception is when a
CharField
has both unique=True
and blank=True
set. In this
situation, null=True
is required to avoid unique constraint violations when
saving multiple objects with blank values.
For both string-based and non-string-based 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
).
Note
When using the Oracle database backend, the value NULL
will be stored to
denote the empty string regardless of this attribute.
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
¶
A mapping or iterable in the format described below to use as choices for this field. If choices are given, they’re enforced by model validation and the default form widget will be a select box with these choices instead of the standard text field.
If a mapping is given, the key element is the actual value to be set on the model, and the second element is the human readable name. For example:
YEAR_IN_SCHOOL_CHOICES = {
"FR": "Freshman",
"SO": "Sophomore",
"JR": "Junior",
"SR": "Senior",
"GR": "Graduate",
}
You can also pass a sequence consisting itself of iterables of exactly
two items (e.g. [(A1, B1), (A2, B2), …]
). The first element in each tuple
is the actual value to be set on the model, and the second element is the
human-readable name. For example:
YEAR_IN_SCHOOL_CHOICES = [
("FR", "Freshman"),
("SO", "Sophomore"),
("JR", "Junior"),
("SR", "Senior"),
("GR", "Graduate"),
]
choices
can also be defined as a callable that expects no arguments and
returns any of the formats described above. For example:
def get_currencies():
return {i: i for i in settings.CURRENCIES}
class Expense(models.Model):
amount = models.DecimalField(max_digits=10, decimal_places=2)
currency = models.CharField(max_length=3, choices=get_currencies)
Passing a callable for choices
can be particularly handy when, for example,
the choices are:
the result of I/O-bound operations (which could potentially be cached), such as querying a table in the same or an external database, or accessing the choices from a static file.
a list that is mostly stable but could vary from time to time or from project to project. Examples in this category are using third-party apps that provide a well-known inventory of values, such as currencies, countries, languages, time zones, etc.
Generally, it’s best to define choices inside a model class, and to define a suitably-named constant for each value:
from django.db import models
class Student(models.Model):
FRESHMAN = "FR"
SOPHOMORE = "SO"
JUNIOR = "JR"
SENIOR = "SR"
GRADUATE = "GR"
YEAR_IN_SCHOOL_CHOICES = {
FRESHMAN: "Freshman",
SOPHOMORE: "Sophomore",
JUNIOR: "Junior",
SENIOR: "Senior",
GRADUATE: "Graduate",
}
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 helps reference the choices (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 key of the mapping is the name to apply to the group and the value is the
choices inside that group, consisting of the field value and a human-readable
name for an option. Grouped options may be combined with ungrouped options
within a single mapping (such as the "unknown"
option in this example).
You can also use a sequence, e.g. a list of 2-tuples:
MEDIA_CHOICES = [
(
"Audio",
(
("vinyl", "Vinyl"),
("cd", "CD"),
),
),
(
"Video",
(
("vhs", "VHS Tape"),
("dvd", "DVD"),
),
),
("unknown", "Unknown"),
]
Note that choices can be any sequence 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.
Note
A new migration is created each time the order of choices
changes.
For each model field that has choices
set, Django will normalize
the choices to a list of 2-tuples and add a method to retrieve the
human-readable name for the field’s current value. See
get_FOO_display()
in the database API
documentation.
Unless blank=False
is set on the field along with a
default
then a label containing "---------"
will be rendered
with the select box. To override this behavior, add a tuple to choices
containing None
; e.g. (None, 'Your String For Display')
.
Alternatively, you can use an empty string instead of None
where this makes
sense - such as on a CharField
.
Enumeration types¶
In addition, Django provides enumeration types that you can subclass to define choices in a concise way:
from django.utils.translation import gettext_lazy as _
class Student(models.Model):
class YearInSchool(models.TextChoices):
FRESHMAN = "FR", _("Freshman")
SOPHOMORE = "SO", _("Sophomore")
JUNIOR = "JR", _("Junior")
SENIOR = "SR", _("Senior")
GRADUATE = "GR", _("Graduate")
year_in_school = models.CharField(
max_length=2,
choices=YearInSchool,
default=YearInSchool.FRESHMAN,
)
def is_upperclass(self):
return self.year_in_school in {
self.YearInSchool.JUNIOR,
self.YearInSchool.SENIOR,
}
These work similar to enum
from Python’s standard library, but with some
modifications:
Enum member values are a tuple of arguments to use when constructing the concrete data type. Django supports adding an extra string value to the end of this tuple to be used as the human-readable name, or
label
. Thelabel
can be a lazy translatable string. Thus, in most cases, the member value will be a(value, label)
2-tuple. See below for an example of subclassing choices using a more complex data type. If a tuple is not provided, or the last item is not a (lazy) string, thelabel
is automatically generated from the member name.A
.label
property is added on values, to return the human-readable name.A number of custom properties are added to the enumeration classes –
.choices
,.labels
,.values
, and.names
– to make it easier to access lists of those separate parts of the enumeration.Warning
These property names cannot be used as member names as they would conflict.
The use of
enum.unique()
is enforced to ensure that values cannot be defined multiple times. This is unlikely to be expected in choices for a field.
Note that using YearInSchool.SENIOR
, YearInSchool['SENIOR']
, or
YearInSchool('SR')
to access or lookup enum members work as expected, as do
the .name
and .value
properties on the members.
If you don’t need to have the human-readable names translated, you can have them inferred from the member name (replacing underscores with spaces and using title-case):
>>> class Vehicle(models.TextChoices):
... CAR = "C"
... TRUCK = "T"
... JET_SKI = "J"
...
>>> Vehicle.JET_SKI.label
'Jet Ski'
Since the case where the enum values need to be integers is extremely common,
Django provides an IntegerChoices
class. For example:
class Card(models.Model):
class Suit(models.IntegerChoices):
DIAMOND = 1
SPADE = 2
HEART = 3
CLUB = 4
suit = models.IntegerField(choices=Suit)
It is also possible to make use of the Enum Functional API with the caveat that labels are automatically generated as highlighted above:
>>> MedalType = models.TextChoices("MedalType", "GOLD SILVER BRONZE")
>>> MedalType.choices
[('GOLD', 'Gold'), ('SILVER', 'Silver'), ('BRONZE', 'Bronze')]
>>> Place = models.IntegerChoices("Place", "FIRST SECOND THIRD")
>>> Place.choices
[(1, 'First'), (2, 'Second'), (3, 'Third')]
If you require support for a concrete data type other than int
or str
,
you can subclass Choices
and the required concrete data type, e.g.
date
for use with DateField
:
class MoonLandings(datetime.date, models.Choices):
APOLLO_11 = 1969, 7, 20, "Apollo 11 (Eagle)"
APOLLO_12 = 1969, 11, 19, "Apollo 12 (Intrepid)"
APOLLO_14 = 1971, 2, 5, "Apollo 14 (Antares)"
APOLLO_15 = 1971, 7, 30, "Apollo 15 (Falcon)"
APOLLO_16 = 1972, 4, 21, "Apollo 16 (Orion)"
APOLLO_17 = 1972, 12, 11, "Apollo 17 (Challenger)"
There are some additional caveats to be aware of:
Enumeration types do not support named groups.
Because an enumeration with a concrete data type requires all values to match the type, overriding the blank label cannot be achieved by creating a member with a value of
None
. Instead, set the__empty__
attribute on the class:class Answer(models.IntegerChoices): NO = 0, _("No") YES = 1, _("Yes") __empty__ = _("(Unknown)")
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_comment
¶
- Field.db_comment¶
The comment on the database column to use for this field. It is useful for documenting fields for individuals with direct database access who may not be looking at your Django code. For example:
pub_date = models.DateTimeField(
db_comment="Date and time when the article was published",
)
db_default
¶
- Field.db_default¶
The database-computed default value for this field. This can be a literal value
or a database function, such as Now
:
created = models.DateTimeField(db_default=Now())
More complex expressions can be used, as long as they are made from literals and database functions:
month_due = models.DateField(
db_default=TruncMonth(
Now() + timedelta(days=90),
output_field=models.DateField(),
)
)
Database defaults cannot reference other fields or models. For example, this is invalid:
end = models.IntegerField(db_default=F("start") + 50)
If both db_default
and Field.default
are set, default
will take
precedence when creating instances in Python code. db_default
will still be
set at the database level and will be used when inserting rows outside of the
ORM or when adding a new field in a migration.
If a field has a db_default
without a default
set and no value is
assigned to the field, a DatabaseDefault
object is returned as the field
value on unsaved model instances. The actual value for the field is determined
by the database when the model instance is saved.
db_index
¶
- Field.db_index¶
If True
, a database index will be created for this 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 can’t 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 want to specify a default dict
for
JSONField
, use a function:
def contact_default():
return {"email": "to1@example.com"}
contact_info = JSONField("ContactInfo", default=contact_default)
lambda
s can’t be used for field options like default
because they
can’t be serialized by migrations. See that
documentation for other caveats.
For fields like ForeignKey
that map to model instances, defaults
should be the value of the field they reference (pk
unless
to_field
is set) instead of model instances.
The default value is used when new model instances are created and a value
isn’t provided for the field. When the field is a primary key, the default is
also used when the field is set to None
.
The default value can also be set at the database level with
Field.db_default
.
editable
¶
- Field.editable¶
If False
, the field will not be displayed in the admin or any other
ModelForm
. They are also skipped during model
validation. Default is True
.
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
,
unique
, and unique_for_date
. Additional error message keys are
specified for each field in the Field types section below.
These error messages often don’t propagate to forms. See Considerations regarding model’s error_messages.
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. Ensure
that you escape any help text that may come from untrusted users to avoid a
cross-site scripting attack.
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 a field 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. The type of auto-created primary key fields can
be specified per app in AppConfig.default_auto_field
or globally in the
DEFAULT_AUTO_FIELD
setting. For more, see
Automatic primary key fields.
primary_key=True
implies null=False
and
unique=True
. Only one primary key is allowed on an
object.
The primary key field is read-only. If you change the value of the primary key on an existing object and then save it, a new object will be created alongside the old one.
The primary key field is set to None
when
deleting
an object.
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
OneToOneField
.
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
.
Note that if you set this to point to a DateTimeField
, only the date
portion of the field will be considered. Besides, when USE_TZ
is
True
, the check will be performed in the current time zone at the time the object gets saved.
This is enforced by Model.validate_unique()
during model validation
but not at the database level. If any unique_for_date
constraint
involves fields that are not part of a ModelForm
(for
example, if one of the fields is listed in exclude
or has
editable=False
), Model.validate_unique()
will
skip validation for that particular constraint.
unique_for_month
¶
- Field.unique_for_month¶
Like unique_for_date
, but requires the field to be unique with
respect to the month.
unique_for_year
¶
- Field.unique_for_year¶
Like unique_for_date
and unique_for_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
¶
A list of validators to run for this field. See the validators documentation for more information.
Field types¶
AutoField
¶
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 Automatic primary key fields.
BigAutoField
¶
A 64-bit integer, much like an AutoField
except that it is
guaranteed to fit numbers from 1
to 9223372036854775807
.
BigIntegerField
¶
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
NumberInput
.
BinaryField
¶
A field to store raw binary data. It can be assigned bytes
,
bytearray
, or memoryview
.
By default, BinaryField
sets editable
to False
, in which
case it can’t be included in a ModelForm
.
- BinaryField.max_length¶
Optional. The maximum length (in bytes) of the field. The maximum length is enforced in Django’s validation using
MaxLengthValidator
.
Abusing BinaryField
Although you might think about storing files in the database, consider that it is bad design in 99% of the cases. This field is not a replacement for proper static files handling.
BooleanField
¶
A true/false field.
The default form widget for this field is CheckboxInput
,
or NullBooleanSelect
if null=True
.
The default value of BooleanField
is None
when Field.default
isn’t defined.
CompositePrimaryKey
¶
A virtual field used for defining a composite primary key.
This field must be defined as the model’s pk
field. If present, Django will
create the underlying model table with a composite primary key.
The *field_names
argument is a list of positional field names that compose
the primary key.
See Composite primary keys for more details.
CharField
¶
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 the following extra arguments:
- 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 usingMaxLengthValidator
. It’s required for all database backends included with Django except PostgreSQL and SQLite, which supports unlimitedVARCHAR
columns.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.Changed in Django Development version:Support for unlimited
VARCHAR
columns was added on SQLite.
- CharField.db_collation¶
Optional. The database collation name of the field.
Note
Collation names are not standardized. As such, this will not be portable across multiple database backends.
Oracle
Oracle supports collations only when the
MAX_STRING_SIZE
database initialization parameter is set toEXTENDED
.
DateField
¶
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.
The field is only automatically updated when calling
Model.save()
. The field isn’t updated when making updates to other fields in other ways such asQuerySet.update()
, though you can specify a custom value for the field in an update like that.
- 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. So even if you set a value for this field when creating the object, it will be ignored. If you want to be able to modify this field, set the following instead of
auto_now_add=True
:For
DateField
:default=date.today
- fromdatetime.date.today()
For
DateTimeField
:default=timezone.now
- fromdjango.utils.timezone.now()
The default form widget for this field is a
DateInput
. The admin adds a JavaScript calendar,
and a shortcut for “Today”. Includes an additional invalid_date
error
message key.
The options auto_now_add
, auto_now
, and default
are mutually exclusive.
Any combination of these options will result in an error.
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.
Note
The auto_now
and auto_now_add
options will always use the date in
the default timezone at the moment of
creation or update. If you need something different, you may want to
consider using your own callable default or overriding save()
instead
of using auto_now
or auto_now_add
; or using a DateTimeField
instead of a DateField
and deciding how to handle the conversion from
datetime to date at display time.
Warning
Always use DateField
with a datetime.date
instance.
If you have a datetime.datetime
instance, it’s recommended to convert
it to a datetime.date
first. If you don’t, DateField
will
localize the datetime.datetime
to the default timezone and convert it to a datetime.date
instance, removing its time component. This is true for both storage and
comparison.
DateTimeField
¶
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
DateTimeInput
. The admin uses two separate
TextInput
widgets with JavaScript shortcuts.
Warning
Always use DateTimeField
with a datetime.datetime
instance.
If you have a datetime.date
instance, it’s recommended to convert it to
a datetime.datetime
first. If you don’t, DateTimeField
will
use midnight in the default timezone for
the time component. This is true for both storage and comparison. To
compare the date portion of a DateTimeField
with a
datetime.date
instance, use the date
lookup.
DecimalField
¶
A fixed-precision decimal number, represented in Python by a
Decimal
instance. It validates the input using
DecimalValidator
.
Has the following 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
.
- DecimalField.decimal_places¶
The number of decimal places to store with the number.
For example, to store numbers up to 999.99
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 NumberInput
when localize
is False
or
TextInput
otherwise.
Note
For more information about the differences between the
FloatField
and DecimalField
classes, please
see FloatField vs. DecimalField. You
should also be aware of SQLite limitations
of decimal fields.
DurationField
¶
A field for storing periods of time - modeled in Python by
timedelta
. When used on PostgreSQL, the data type
used is an interval
and on Oracle the data type is INTERVAL DAY(9) TO
SECOND(6)
. Otherwise a bigint
of microseconds is used.
Note
Arithmetic with DurationField
works in most cases. However on all
databases other than PostgreSQL, comparing the value of a DurationField
to arithmetic on DateTimeField
instances will not work as expected.
EmailField
¶
A CharField
that checks that the value is a valid email address using
EmailValidator
.
FileField
¶
A file-upload field.
Note
The primary_key
argument isn’t supported and will raise an error if
used.
Has the following optional arguments:
- FileField.upload_to¶
This attribute provides a way of setting the upload directory and file name, and can be set in two ways. In both cases, the value is passed to the
Storage.save()
method.If you specify a string value or a
Path
, it may containstrftime()
formatting, which will be replaced by the date/time of the file upload (so that uploaded files don’t fill up the given directory). For example:class MyModel(models.Model): # file will be uploaded to MEDIA_ROOT/uploads upload = models.FileField(upload_to="uploads/") # or... # file will be saved to MEDIA_ROOT/uploads/2015/01/30 upload = models.FileField(upload_to="uploads/%Y/%m/%d/")
If you are using the default
FileSystemStorage
, the string value will be appended to yourMEDIA_ROOT
path to form the location on the local filesystem where uploaded files will be stored. If you are using a different storage, check that storage’s documentation to see how it handlesupload_to
.upload_to
may also be a callable, such as a function. This will be called to obtain the upload path, including the filename. This callable must accept two arguments and return a Unix-style path (with forward slashes) to be passed along to the storage system. The two arguments 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.
For example:
def user_directory_path(instance, filename): # file will be uploaded to MEDIA_ROOT/user_<id>/<filename> return "user_{0}/{1}".format(instance.user.id, filename) class MyModel(models.Model): upload = models.FileField(upload_to=user_directory_path)
- FileField.storage¶
A storage object, or a callable which returns a storage object. This 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
ClearableFileInput
.
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, defining theupload_to
option to specify a subdirectory ofMEDIA_ROOT
to use for uploaded 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.
FileField
instances are created in your database as varchar
columns with a default max length of 100 characters. As with other fields, you
can change the maximum length using the max_length
argument.
FileField
and FieldFile
¶
When you access a FileField
on a model, you are
given an instance of FieldFile
as a proxy for accessing the underlying
file.
The API of FieldFile
mirrors that of File
,
with one key difference: The object wrapped by the class is not necessarily a
wrapper around Python’s built-in file object. Instead, it is a wrapper around
the result of the Storage.open()
method, which may be a File
object, or it may be a
custom storage’s implementation of the File
API.
In addition to the API inherited from File
such as
read()
and write()
, FieldFile
includes several methods that
can be used to interact with the underlying file:
Warning
Two methods of this class, save()
and
delete()
, default to saving the model object of the
associated FieldFile
in the database.
- FieldFile.name¶
The name of the file including the relative path from the root of the
Storage
of the associated
FileField
.
A read-only property to access the file’s local filesystem path by calling the
path()
method of the underlying
Storage
class.
The result of the underlying Storage.size()
method.
A read-only property to access the file’s relative URL by calling the
url()
method of the underlying
Storage
class.
Opens or reopens the file associated with this instance in the specified
mode
. Unlike the standard Python open()
method, it doesn’t return a
file descriptor.
Since the underlying file is opened implicitly when accessing it, it may be
unnecessary to call this method except to reset the pointer to the underlying
file or to change the mode
.
Behaves like the standard Python file.close()
method and closes the file
associated with this instance.
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 model instance is
saved after the file associated with this field 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("/path/to/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.
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 model instance is
saved after the file associated with this field 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='', match=None, recursive=False, allow_files=True, allow_folders=False, max_length=100, **options)[source]¶
A CharField
whose choices are limited to the filenames in a certain
directory on the filesystem. Has some 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"
.path
may also be a callable, such as a function to dynamically set the path at runtime. Example:import os from django.conf import settings from django.db import models def images_path(): return os.path.join(settings.LOCAL_FILE_DIR, "images") class MyModel(models.Model): file = models.FilePathField(path=images_path)
- 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
.
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
).
FilePathField
instances are created in your database as varchar
columns with a default max length of 100 characters. As with other fields, you
can change the maximum length using the max_length
argument.
FloatField
¶
A floating-point number represented in Python by a float
instance.
The default form widget for this field is a NumberInput
when localize
is False
or
TextInput
otherwise.
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.
GeneratedField
¶
A field that is always computed based on other fields in the model. This field
is managed and updated by the database itself. Uses the GENERATED ALWAYS
SQL syntax.
There are two kinds of generated columns: stored and virtual. A stored generated column is computed when it is written (inserted or updated) and occupies storage as if it were a regular column. A virtual generated column occupies no storage and is computed when it is read. Thus, a virtual generated column is similar to a view and a stored generated column is similar to a materialized view.
- GeneratedField.expression¶
An
Expression
used by the database to automatically set the field value each time the model is changed.The expressions should be deterministic and only reference fields within the model (in the same database table). Generated fields cannot reference other generated fields. Database backends can impose further restrictions.
- GeneratedField.output_field¶
A model field instance to define the field’s data type.
- GeneratedField.db_persist¶
Determines if the database column should occupy storage as if it were a real column. If
False
, the column acts as a virtual column and does not occupy database storage space.PostgreSQL only supports persisted columns. Oracle only supports virtual columns.
Refresh the data
Since the database always computed the value, the object must be reloaded
to access the new value after save()
, for example, by using
refresh_from_db()
.
Database limitations
There are many database-specific restrictions on generated fields that
Django doesn’t validate and the database may raise an error e.g. PostgreSQL
requires functions and operators referenced in a generated column to be
marked as IMMUTABLE
.
You should always check that expression
is supported on your database.
Check out MariaDB, MySQL, Oracle, PostgreSQL, or SQLite
docs.
GenericIPAddressField
¶
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'
.
If you allow for blank values, you have to allow for null values since blank values are stored as null.
ImageField
¶
- class ImageField(upload_to=None, height_field=None, width_field=None, max_length=100, **options)[source]¶
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 the
following optional arguments:
- ImageField.height_field¶
Name of a model field which is auto-populated with the height of the image each time an image object is set.
- ImageField.width_field¶
Name of a model field which is auto-populated with the width of the image each time an image object is set.
Requires the pillow library.
ImageField
instances are created in your database as varchar
columns with a default max length of 100 characters. As with other fields, you
can change the maximum length using the max_length
argument.
The default form widget for this field is a
ClearableFileInput
.
IntegerField
¶
An integer. Values from -2147483648
to 2147483647
are safe in all
databases supported by Django.
It uses MinValueValidator
and
MaxValueValidator
to validate the input based
on the values that the default database supports.
The default form widget for this field is a NumberInput
when localize
is False
or
TextInput
otherwise.
JSONField
¶
A field for storing JSON encoded data. In Python the data is represented in its
Python native format: dictionaries, lists, strings, numbers, booleans and
None
.
JSONField
is supported on MariaDB, MySQL, Oracle, PostgreSQL, and SQLite
(with the JSON1 extension enabled).
- JSONField.encoder¶
An optional
json.JSONEncoder
subclass to serialize data types not supported by the standard JSON serializer (e.g.datetime.datetime
orUUID
). For example, you can use theDjangoJSONEncoder
class.Defaults to
json.JSONEncoder
.
- JSONField.decoder¶
An optional
json.JSONDecoder
subclass to deserialize the value retrieved from the database. The value will be in the format chosen by the custom encoder (most often a string). Your deserialization may need to account for the fact that you can’t be certain of the input type. For example, you run the risk of returning adatetime
that was actually a string that just happened to be in the same format chosen fordatetime
s.Defaults to
json.JSONDecoder
.
To query JSONField
in the database, see Querying JSONField.
Default value
If you give the field a default
, ensure
it’s a callable such as the dict
class or a function that
returns a fresh object each time. Incorrectly using a mutable object like
default={}
or default=[]
creates a mutable default that is shared
between all instances.
Indexing
Index
and Field.db_index
both create a
B-tree index, which isn’t particularly helpful when querying JSONField
.
On PostgreSQL only, you can use
GinIndex
that is better suited.
PostgreSQL users
PostgreSQL has two native JSON based data types: json
and jsonb
.
The main difference between them is how they are stored and how they can be
queried. PostgreSQL’s json
field is stored as the original string
representation of the JSON and must be decoded on the fly when queried
based on keys. The jsonb
field is stored based on the actual structure
of the JSON which allows indexing. The trade-off is a small additional cost
on writing to the jsonb
field. JSONField
uses jsonb
.
PositiveBigIntegerField
¶
Like a PositiveIntegerField
, but only allows values under a certain
(database-dependent) point. Values from 0
to 9223372036854775807
are
safe in all databases supported by Django.
PositiveIntegerField
¶
Like an IntegerField
, but must be either positive or zero (0
).
Values from 0
to 2147483647
are safe in all databases supported by
Django. The value 0
is accepted for backward compatibility reasons.
PositiveSmallIntegerField
¶
Like a PositiveIntegerField
, but only allows values under a certain
(database-dependent) point. Values from 0
to 32767
are safe in all
databases supported by Django.
SlugField
¶
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
.
It uses validate_slug
or
validate_unicode_slug
for validation.
- SlugField.allow_unicode¶
If
True
, the field accepts Unicode letters in addition to ASCII letters. Defaults toFalse
.
SmallAutoField
¶
Like an AutoField
, but only allows values under a certain
(database-dependent) limit. Values from 1
to 32767
are safe in all
databases supported by Django.
SmallIntegerField
¶
Like an IntegerField
, but only allows values under a certain
(database-dependent) point. Values from -32768
to 32767
are safe in all
databases supported by Django.
TextField
¶
A large text field. The default form widget for this field is a
Textarea
.
If you specify a max_length
attribute, it will be reflected in the
Textarea
widget of the auto-generated form field.
However it is not enforced at the model or database level. Use a
CharField
for that.
- TextField.db_collation¶
Optional. The database collation name of the field.
Note
Collation names are not standardized. As such, this will not be portable across multiple database backends.
Oracle
Oracle does not support collations for a
TextField
.
TimeField
¶
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 TimeInput
.
The admin adds some JavaScript shortcuts.
URLField
¶
A CharField
for a URL, validated by
URLValidator
.
The default form widget for this field is a URLInput
.
Like all CharField
subclasses, URLField
takes the optional
max_length
argument. If you don’t specify
max_length
, a default of 200 is used.
UUIDField
¶
A field for storing universally unique identifiers. Uses Python’s
UUID
class. When used on PostgreSQL and MariaDB 10.7+,
this stores in a uuid
datatype, otherwise in a char(32)
.
Universally unique identifiers are a good alternative to AutoField
for
primary_key
. The database will not generate the UUID for you, so
it is recommended to use default
:
import uuid
from django.db import models
class MyUUIDModel(models.Model):
id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
# other fields
Note that a callable (with the parentheses omitted) is passed to default
,
not an instance of UUID
.
Lookups on PostgreSQL and MariaDB 10.7+
Using iexact
, contains
, icontains
,
startswith
, istartswith
, endswith
, or
iendswith
lookups on PostgreSQL don’t work for values without
hyphens, because PostgreSQL and MariaDB 10.7+ store them in a hyphenated
uuid datatype type.
Field API reference¶
- class Field[source]¶
Field
is an abstract class that represents a database table column. Django uses fields to create the database table (db_type()
), to map Python types to database (get_prep_value()
) and vice-versa (from_db_value()
).A field is thus a fundamental piece in different Django APIs, notably,
models
andquerysets
.In models, a field is instantiated as a class attribute and represents a particular table column, see Models. It has attributes such as
null
andunique
, and methods that Django uses to map the field value to database-specific values.A
Field
is a subclass ofRegisterLookupMixin
and thus bothTransform
andLookup
can be registered on it to be used inQuerySet
s (e.g.field_name__exact="foo"
). All built-in lookups are registered by default.All of Django’s built-in fields, such as
CharField
, are particular implementations ofField
. If you need a custom field, you can either subclass any of the built-in fields or write aField
from scratch. In either case, see How to create custom model fields.- description¶
A verbose description of the field, e.g. for the
django.contrib.admindocs
application.The description can be of the form:
description = _("String (up to %(max_length)s)")
where the arguments are interpolated from the field’s
__dict__
.
- descriptor_class¶
A class implementing the descriptor protocol that is instantiated and assigned to the model instance attribute. The constructor must accept a single argument, the
Field
instance. Overriding this class attribute allows for customizing the get and set behavior.
To map a
Field
to a database-specific type, Django exposes several methods:- get_internal_type()[source]¶
Returns a string naming this field for backend specific purposes. By default, it returns the class name.
See Emulating built-in field types for usage in custom fields.
- db_type(connection)[source]¶
Returns the database column data type for the
Field
, taking into account theconnection
.See Custom database types for usage in custom fields.
- rel_db_type(connection)[source]¶
Returns the database column data type for fields such as
ForeignKey
andOneToOneField
that point to theField
, taking into account theconnection
.See Custom database types for usage in custom fields.
There are three main situations where Django needs to interact with the database backend and fields:
when it queries the database (Python value -> database backend value)
when it loads data from the database (database backend value -> Python value)
when it saves to the database (Python value -> database backend value)
When querying,
get_db_prep_value()
andget_prep_value()
are used:- get_prep_value(value)[source]¶
value
is the current value of the model’s attribute, and the method should return data in a format that has been prepared for use as a parameter in a query.See Converting Python objects to query values for usage.
- get_db_prep_value(value, connection, prepared=False)[source]¶
Converts
value
to a backend-specific value. By default it returnsvalue
ifprepared=True
andget_prep_value()
if isFalse
.See Converting query values to database values for usage.
When loading data,
from_db_value()
is used:- from_db_value(value, expression, connection)¶
Converts a value as returned by the database to a Python object. It is the reverse of
get_prep_value()
.This method is not used for most built-in fields as the database backend already returns the correct Python type, or the backend itself does the conversion.
expression
is the same asself
.See Converting values to Python objects for usage.
Note
For performance reasons,
from_db_value
is not implemented as a no-op on fields which do not require it (all Django fields). Consequently you may not callsuper
in your definition.
When saving,
pre_save()
andget_db_prep_save()
are used:- get_db_prep_save(value, connection)[source]¶
Same as the
get_db_prep_value()
, but called when the field value must be saved to the database. By default returnsget_db_prep_value()
.
- pre_save(model_instance, add)[source]¶
Method called prior to
get_db_prep_save()
to prepare the value before being saved (e.g. forDateField.auto_now
).model_instance
is the instance this field belongs to andadd
is whether the instance is being saved to the database for the first time.It should return the value of the appropriate attribute from
model_instance
for this field. The attribute name is inself.attname
(this is set up byField
).See Preprocessing values before saving for usage.
Fields often receive their values as a different type, either from serialization or from forms.
- to_python(value)[source]¶
Converts the value into the correct Python object. It acts as the reverse of
value_to_string()
, and is also called inclean()
.See Converting values to Python objects for usage.
Besides saving to the database, the field also needs to know how to serialize its value:
- value_from_object(obj)[source]¶
Returns the field’s value for the given model instance.
This method is often used by
value_to_string()
.
- value_to_string(obj)[source]¶
Converts
obj
to a string. Used to serialize the value of the field.See Converting field data for serialization for usage.
When using
model forms
, theField
needs to know which form field it should be represented by:- formfield(form_class=None, choices_form_class=None, **kwargs)[source]¶
Returns the default
django.forms.Field
of this field forModelForm
.If
formfield()
is overridden to returnNone
, this field is excluded from theModelForm
.By default, if both
form_class
andchoices_form_class
areNone
, it usesCharField
. If the field haschoices
andchoices_form_class
isn’t specified, it usesTypedChoiceField
.See Specifying the form field for a model field for usage.
- deconstruct()[source]¶
Returns a 4-tuple with enough information to recreate the field:
The name of the field on the model.
The import path of the field (e.g.
"django.db.models.IntegerField"
). This should be the most portable version, so less specific may be better.A list of positional arguments.
A dict of keyword arguments.
This method must be added to fields prior to 1.7 to migrate its data using Migrations.
Registering and fetching lookups¶
Field
implements the lookup registration API.
The API can be used to customize which lookups are available for a field class
and its instances, and how lookups are fetched from a field.
Field attribute reference¶
Every Field
instance contains several attributes that allow
introspecting its behavior. Use these attributes instead of isinstance
checks when you need to write code that depends on a field’s functionality.
These attributes can be used together with the Model._meta API to narrow down a search for specific field types.
Custom model fields should implement these flags.
Attributes for fields¶
- Field.auto_created¶
Boolean flag that indicates if the field was automatically created, such as the
OneToOneField
used by model inheritance.
- Field.concrete¶
Boolean flag that indicates if the field has a database column associated with it.
Boolean flag that indicates if a field is hidden and should not be returned by
Options.get_fields()
by default. An example is the reverse field for aForeignKey
with arelated_name
that starts with'+'
.
- Field.is_relation¶
Boolean flag that indicates if a field contains references to one or more other models for its functionality (e.g.
ForeignKey
,ManyToManyField
,OneToOneField
, etc.).
- Field.model¶
Returns the model on which the field is defined. If a field is defined on a superclass of a model,
model
will refer to the superclass, not the class of the instance.
Attributes for fields with relations¶
These attributes are used to query for the cardinality and other details of a
relation. These attribute are present on all fields; however, they will only
have boolean values (rather than None
) if the field is a relation type
(Field.is_relation=True
).
- Field.many_to_many¶
Boolean flag that is
True
if the field has a many-to-many relation;False
otherwise. The only field included with Django where this isTrue
isManyToManyField
.
- Field.many_to_one¶
Boolean flag that is
True
if the field has a many-to-one relation, such as aForeignKey
;False
otherwise.
- Field.one_to_many¶
Boolean flag that is
True
if the field has a one-to-many relation, such as aGenericRelation
or the reverse of aForeignKey
;False
otherwise.
- Field.one_to_one¶
Boolean flag that is
True
if the field has a one-to-one relation, such as aOneToOneField
;False
otherwise.
Points to the model the field relates to. For example,
Author
inForeignKey(Author, on_delete=models.CASCADE)
. Therelated_model
for aGenericForeignKey
is alwaysNone
.