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.
Changed in Django 5.0: 
Support for mappings and callables was added.




    

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.
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. The
label 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, the label 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)")
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",
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.
db_index¶
Field.db_index¶
If True, a database index will be created for this field.
Use the indexes option instead.
Where possible, use the Meta.indexes option
instead. In nearly all cases, indexes provides more
functionality than db_index. db_index may be deprecated in the
future.
db_tablespace¶
Field.db_tablespace[source]¶
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": "[email protected]"}
contact_info = JSONField("ContactInfo", default=contact_default)
lambdas 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¶
Field.error_messages[source]¶
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¶
Field.unique[source]¶
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¶
Field.validators[source]¶
A list of validators to run for this field. See the validators
documentation for more information.
Field types¶
AutoField¶
class AutoField(**options)[source]¶
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¶
class BigAutoField(**options)[source]¶
A 64-bit integer, much like an AutoField except that it is
guaranteed to fit numbers from 1 to 9223372036854775807.
BigIntegerField¶
class BigIntegerField(**options)[source]¶
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¶
class BinaryField(max_length=None, **options)[source]¶
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¶
class BooleanField(**options)[source]¶
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.
CharField¶
class CharField(max_length=None, **options)[source]¶
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 using
MaxLengthValidator. It’s required for all
database backends included with Django except PostgreSQL, which supports
unlimited VARCHAR columns.
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.
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 to EXTENDED.
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 as QuerySet.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 - from
datetime.date.today()
For DateTimeField: default=timezone.now - from
django.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.
As currently implemented, setting auto_now or auto_now_add to
True will cause the field to have editable=False and blank=True
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¶
class DateTimeField(auto_now=False, auto_now_add=False, **options)[source]¶
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¶
class DecimalField(max_digits=None, decimal_places=None, **options)[source]¶
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.
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.
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¶
class DurationField(**options)[source]¶
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.
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¶
class EmailField(max_length=254, **options)[source]¶
A CharField that checks that the value is a valid email address using
EmailValidator.
FileField¶
class FileField(upload_to='', storage=None, max_length=100, **options)[source]¶
A file-upload field.
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 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). 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 your MEDIA_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
handles upload_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:
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.) Define
MEDIA_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 or ImageField to your model, defining
the upload_to option to specify a subdirectory of
MEDIA_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
convenience url attribute
provided by Django. For example, if your ImageField is called
mug_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.
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¶
class FieldFile[source]¶
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.
FieldFile.path[source]¶
A read-only property to access the file’s local filesystem path by calling the
path() method of the underlying
Storage class.
FieldFile.size[source]¶
The result of the underlying Storage.size() method.
FieldFile.url[source]¶
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')[source]¶
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.
FieldFile.close()[source]¶
Behaves like the standard Python file.close() method and closes the file
associated with this instance.
FieldFile.save(name, content, save=True)[source]¶
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.
FieldFile.delete(save=True)[source]¶
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 called foo23.txt but not bar.txt or foo23.png.
FilePathField.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.
FilePathField.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.
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¶
class FloatField(**options)[source]¶
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¶
New in Django 5.0. 




    

class GeneratedField(expression, output_field, db_persist=None, **kwargs)[source]¶
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.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¶
class GenericIPAddressField(protocol='both', unpack_ipv4=False, **options)[source]¶
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 to
192.0.2.1. Default is disabled. Can only be used
when protocol 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¶
class IntegerField(**options)[source]¶
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¶
class JSONField(encoder=None, decoder=None, **options)[source]¶
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
or UUID). For example, you can use the
DjangoJSONEncoder 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 a datetime that was actually a
string that just happened to be in the same format chosen for
datetimes.
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.
Oracle users
Oracle Database does not support storing JSON scalar values. Only JSON
objects and arrays (represented in Python using dict and
list) are supported.
PositiveBigIntegerField¶
class PositiveBigIntegerField(**options)[source]¶
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¶
class PositiveIntegerField(**options)[source]¶
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¶
class PositiveSmallIntegerField(**options)[source]¶
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¶
class SlugField(max_length=50, **options)[source]¶
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 to False.
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¶
class SmallIntegerField(**options)[source]¶
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¶
class TextField(**options)[source]¶
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.
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.
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¶
class URLField(max_length=200, **options)[source]¶
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¶
class UUIDField(**options)[source]¶
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.
A many-to-one relationship. Requires two positional arguments: the class to
which the model is related and the on_delete option.
To create a recursive relationship – an object that has a many-to-one
relationship with itself – use models.ForeignKey('self',
on_delete=models.CASCADE).
If you need to create a relationship on a model that has not yet been defined,
you can use the name of the model, rather than the model object itself:
from django.db import models
class Car(models.Model):
    manufacturer = models.ForeignKey(
        "Manufacturer",
        on_delete=models.CASCADE,
    # ...
class Manufacturer(models.Model):
    # ...
Relationships defined this way on abstract models are resolved when the model is subclassed as a
concrete model and are not relative to the abstract model’s app_label:
products/models.py¶




    

from django.db import models
class AbstractCar(models.Model):
    manufacturer = models.ForeignKey("Manufacturer", on_delete=models.CASCADE)
    class Meta:
        abstract = True
production/models.py¶
from django.db import models
from products.models import AbstractCar
class Manufacturer(models.Model):
class Car(AbstractCar):
# Car.manufacturer will point to `production.Manufacturer` here.
To refer to models defined in another application, you can explicitly specify
a model with the full application label. For example, if the Manufacturer
model above is defined in another application called production, you’d
need to use:
class Car(models.Model):
    manufacturer = models.ForeignKey(
        "production.Manufacturer",
        on_delete=models.CASCADE,
This sort of reference, called a lazy relationship, can be useful when
resolving circular import dependencies between two applications.
A database index is automatically created on the ForeignKey. You can
disable this by setting db_index to False.  You may want to
avoid the overhead of an index if you are creating a foreign key for
consistency rather than joins, or if you will be creating an alternative index
like a partial or multiple column index.
Database Representation¶
Behind the scenes, Django appends "_id" to the field name to create its
database column name. In the above example, the database table for the Car
model will have a manufacturer_id column. (You can change this explicitly by
specifying db_column) However, your code should never have to
deal with the database column name, unless you write custom SQL. You’ll always
deal with the field names of your model object.
Arguments¶
ForeignKey accepts other arguments that define the details of how the
relation works.
ForeignKey.on_delete¶
When an object referenced by a ForeignKey is deleted, Django will
emulate the behavior of the SQL constraint specified by the
on_delete argument. For example, if you have a nullable
ForeignKey and you want it to be set null when the referenced
object is deleted:
user = models.ForeignKey(
    User,
    models.SET_NULL,
    blank=True,
    null=True,
on_delete doesn’t create an SQL constraint in the database. Support for
database-level cascade options may be implemented later.
The possible values for on_delete are found in
django.db.models:
CASCADE[source]¶
Cascade deletes. Django emulates the behavior of the SQL constraint ON
DELETE CASCADE and also deletes the object containing the ForeignKey.
Model.delete() isn’t called on related models, but the
pre_delete and
post_delete signals are sent for all
deleted objects.
PROTECT[source]¶
Prevent deletion of the referenced object by raising
ProtectedError, a subclass of
django.db.IntegrityError.
RESTRICT[source]¶
Prevent deletion of the referenced object by raising
RestrictedError (a subclass of
django.db.IntegrityError). Unlike PROTECT, deletion of the
referenced object is allowed if it also references a different object
that is being deleted in the same operation, but via a CASCADE
relationship.




    

Consider this set of models:
class Artist(models.Model):
    name = models.CharField(max_length=10)
class Album(models.Model):
    artist = models.ForeignKey(Artist, on_delete=models.CASCADE)
class Song(models.Model):
    artist = models.ForeignKey(Artist, on_delete=models.CASCADE)
    album = models.ForeignKey(Album, on_delete=models.RESTRICT)
Artist can be deleted even if that implies deleting an Album
which is referenced by a Song, because Song also references
Artist itself through a cascading relationship. For example:
>>> artist_one = Artist.objects.create(name="artist one")
>>> artist_two = Artist.objects.create(name="artist two")
>>> album_one = Album.objects.create(artist=artist_one)
>>> album_two = Album.objects.create(artist=artist_two)
>>> song_one = Song.objects.create(artist=artist_one, album=album_one)
>>> song_two = Song.objects.create(artist=artist_one, album=album_two)
>>> album_one.delete()
# Raises RestrictedError.
>>> artist_two.delete()
# Raises RestrictedError.
>>> artist_one.delete()
(4, {'Song': 2, 'Album': 1, 'Artist': 1})
SET()[source]¶
Set the ForeignKey to the value passed to
SET(), or if a callable is passed in,
the result of calling it. In most cases, passing a callable will be
necessary to avoid executing queries at the time your models.py is
imported:
from django.conf import settings
from django.contrib.auth import get_user_model
from django.db import models
def get_sentinel_user():
    return get_user_model().objects.get_or_create(username="deleted")[0]
class MyModel(models.Model):
    user = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.SET(get_sentinel_user),
DO_NOTHING[source]¶
Take no action. If your database backend enforces referential
integrity, this will cause an IntegrityError unless
you manually add an SQL ON DELETE constraint to the database field.
ForeignKey.limit_choices_to¶
Sets a limit to the available choices for this field when this field is
rendered using a ModelForm or the admin (by default, all objects
in the queryset are available to choose). Either a dictionary, a
Q object, or a callable returning a
dictionary or Q object can be used.
For example:
staff_member = models.ForeignKey(
    User,
    on_delete=models.CASCADE,
    limit_choices_to={"is_staff": True},
causes the corresponding field on the ModelForm to list only Users
that have is_staff=True. This may be helpful in the Django admin.
The callable form can be helpful, for instance, when used in conjunction
with the Python datetime module to limit selections by date range. For
example:
def limit_pub_date_choices():
    return {"pub_date__lte": datetime.date.today()}
limit_choices_to = limit_pub_date_choices
If limit_choices_to is or returns a Q object, which is useful for complex queries, then it will only have an effect on the choices
available in the admin when the field is not listed in
raw_id_fields in the
ModelAdmin for the model.
If a callable is used for limit_choices_to, it will be invoked
every time a new form is instantiated. It may also be invoked when a
model is validated, for example by management commands or the admin.
The admin constructs querysets to validate its form inputs in various
edge cases multiple times, so there is a possibility your callable may
be invoked several times.
ForeignKey.related_name¶
The name to use for the relation from the related object back to this one.
It’s also the default value for related_query_name (the name to use
for the reverse filter name from the target model). See the related
objects documentation for a full explanation
and example. Note that you must set this value when defining relations on
abstract models; and when you do so
some special syntax is available.
If you’d prefer Django not to create a backwards relation, set
related_name to '+' or end it with '+'. For example, this will
ensure that the User model won’t have a backwards relation to this
model:
user = models.ForeignKey(
    User,
    on_delete=models.CASCADE,
    related_name="+",
ForeignKey.related_query_name¶
The name to use for the reverse filter name from the target model. It
defaults to the value of related_name or
default_related_name if set, otherwise it
defaults to the name of the model:
# Declare the ForeignKey with related_query_name
class Tag(models.Model):
    article = models.ForeignKey(
        Article,
        on_delete=models.CASCADE,
        related_name="tags",
        related_query_name="tag",
    name = models.CharField(max_length=255)
# That's now the name of the reverse filter
Article.objects.filter(tag__name="important")
Like related_name, related_query_name supports app label and
class interpolation via some special syntax.




    

ForeignKey.to_field¶
The field on the related object that the relation is to. By default, Django
uses the primary key of the related object. If you reference a different
field, that field must have unique=True.
ForeignKey.db_constraint¶
Controls whether or not a constraint should be created in the database for
this foreign key. The default is True, and that’s almost certainly what
you want; setting this to False can be very bad for data integrity.
That said, here are some scenarios where you might want to do this:
You have legacy data that is not valid.
You’re sharding your database.
If this is set to False, accessing a related object that doesn’t exist
will raise its DoesNotExist exception.
ForeignKey.swappable¶
Controls the migration framework’s reaction if this ForeignKey
is pointing at a swappable model. If it is True - the default -
then if the ForeignKey is pointing at a model which matches
the current value of settings.AUTH_USER_MODEL (or another swappable
model setting) the relationship will be stored in the migration using
a reference to the setting, not to the model directly.
You only want to override this to be False if you are sure your
model should always point toward the swapped-in model - for example,
if it is a profile model designed specifically for your custom user model.
Setting it to False does not mean you can reference a swappable model
even if it is swapped out - False means that the migrations made
with this ForeignKey will always reference the exact model you specify
(so it will fail hard if the user tries to run with a User model you don’t
support, for example).
If in doubt, leave it to its default of True.
A many-to-many relationship. Requires a positional argument: the class to
which the model is related, which works exactly the same as it does for
ForeignKey, including recursive and
lazy relationships.
Related objects can be added, removed, or created with the field’s
RelatedManager.
Database Representation¶
Behind the scenes, Django creates an intermediary join table to represent the
many-to-many relationship. By default, this table name is generated using the
name of the many-to-many field and the name of the table for the model that
contains it. Since some databases don’t support table names above a certain
length, these table names will be automatically truncated and a uniqueness hash
will be used, e.g. author_books_9cdf. You can manually provide the name of
the join table using the db_table option.
Arguments¶
ManyToManyField accepts an extra set of arguments – all optional –
that control how the relationship functions.
ManyToManyField.related_name¶
Same as ForeignKey.related_name.
ManyToManyField.symmetrical¶
Only used in the definition of ManyToManyFields on self. Consider the
following model:
from django.db import models
class Person(models.Model):
    friends = models.ManyToManyField("self")
When Django processes this model, it identifies that it has a
ManyToManyField on itself, and as a result, it doesn’t add a
person_set attribute to the Person class. Instead, the
ManyToManyField is assumed to be symmetrical – that is, if I am
your friend, then you are my friend.
If you do not want symmetry in many-to-many relationships with self, set
symmetrical to False. This will force Django to
add the descriptor for the reverse relationship, allowing
ManyToManyField relationships to be non-symmetrical.
ManyToManyField.through¶
Django will automatically generate a table to manage many-to-many
relationships. However, if you want to manually specify the intermediary
table, you can use the through option to specify
the Django model that represents the intermediate table that you want to
The most common use for this option is when you want to associate
extra data with a many-to-many relationship.
If you don’t want multiple associations between the same instances, add
a UniqueConstraint including the from and to
fields. Django’s automatically generated many-to-many tables include
such a constraint.
Recursive relationships using an intermediary model can’t determine the
reverse accessors names, as they would be the same. You need to set a
related_name to at least one of them. If you’d
prefer Django not to create a backwards relation, set related_name
to '+'.
If you don’t specify an explicit through model, there is still an
implicit through model class you can use to directly access the table
created to hold the association. It has three fields to link the models.
If the source and target models differ, the following fields are
generated:
id: the primary key of the relation.
<containing_model>_id: the id of the model that declares the
ManyToManyField.
<other_model>_id: the id of the model that the
ManyToManyField points to.
If the ManyToManyField points from and to the same model, the following
fields are generated:
id: the primary key of the relation.
from_<model>_id: the id of the instance which points at the
model (i.e. the source instance).
to_<model>_id: the id of the instance to which the relationship
points (i.e. the target model instance).
This class can be used to query associated records for a given model
instance like a normal model:
Model.m2mfield.through.objects.all()
ManyToManyField.through_fields¶
Only used when a custom intermediary model is specified. Django will
normally determine which fields of the intermediary model to use in order
to establish a many-to-many relationship automatically. However,
consider the following models:
from django.db import models
class Person(models.Model):
    name = models.CharField(max_length=50)
class Group(models.Model):
    name = models.CharField(max_length=128)
    members = models.ManyToManyField(
        Person,
        through="Membership",
        through_fields=("group", "person"),
class Membership(models.Model):
    group = models.ForeignKey(Group, on_delete=models.CASCADE)
    person = models.ForeignKey(Person, on_delete=models.CASCADE)
    inviter = models.ForeignKey(
        Person,
        on_delete=models.CASCADE,
        related_name="membership_invites",
    invite_reason = models.CharField(max_length=64)
Membership has two foreign keys to Person (person and
inviter), which makes the relationship ambiguous and Django can’t know
which one to use. In this case, you must explicitly specify which
foreign keys Django should use using through_fields, as in the example
above.




    

through_fields accepts a 2-tuple ('field1', 'field2'), where
field1 is the name of the foreign key to the model the
ManyToManyField is defined on (group in this case), and
field2 the name of the foreign key to the target model (person
in this case).
When you have more than one foreign key on an intermediary model to any
(or even both) of the models participating in a many-to-many relationship,
you must specify through_fields. This also applies to
recursive relationships
when an intermediary model is used and there are more than two
foreign keys to the model, or you want to explicitly specify which two
Django should use.
ManyToManyField.db_table¶
The name of the table to create for storing the many-to-many data. If this
is not provided, Django will assume a default name based upon the names of:
the table for the model defining the relationship and the name of the field
itself.
ManyToManyField.db_constraint¶
Controls whether or not constraints should be created in the database for
the foreign keys in the intermediary table. The default is True, and
that’s almost certainly what you want; setting this to False can be
very bad for data integrity. That said, here are some scenarios where you
might want to do this:
You have legacy data that is not valid.
You’re sharding your database.
It is an error to pass both db_constraint and through.
ManyToManyField.swappable¶
Controls the migration framework’s reaction if this ManyToManyField
is pointing at a swappable model. If it is True - the default -
then if the ManyToManyField is pointing at a model which matches
the current value of settings.AUTH_USER_MODEL (or another swappable
model setting) the relationship will be stored in the migration using
a reference to the setting, not to the model directly.
You only want to override this to be False if you are sure your
model should always point toward the swapped-in model - for example,
if it is a profile model designed specifically for your custom user model.
If in doubt, leave it to its default of True.
ManyToManyField does not support validators.
null has no effect since there is no way to require a
relationship at the database level.
OneToOneField¶
class OneToOneField(to, on_delete, parent_link=False, **options)[source]¶
A one-to-one relationship. Conceptually, this is similar to a
ForeignKey with unique=True, but the
“reverse” side of the relation will directly return a single object.
This is most useful as the primary key of a model which “extends”
another model in some way; Multi-table inheritance is
implemented by adding an implicit one-to-one relation from the child
model to the parent model, for example.
One positional argument is required: the class to which the model will be
related. This works exactly the same as it does for ForeignKey,
including all the options regarding recursive
and lazy relationships.
If you do not specify the related_name argument for the
OneToOneField, Django will use the lowercase name of the current model as
default value.
With the following example:
from django.conf import settings
from django.db import models
class MySpecialUser(models.Model):
    user = models.OneToOneField(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
    supervisor = models.OneToOneField(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
        related_name="supervisor_of",
your resulting User model will have the following attributes:
>>> user = User.objects.get(pk=1)
>>> hasattr(user, "myspecialuser")
>>> hasattr(user, "supervisor_of")
A RelatedObjectDoesNotExist exception is raised when accessing the reverse
relationship if an entry in the related table doesn’t exist. This is a subclass
of the target model’s Model.DoesNotExist exception and can be accessed as an
attribute of the reverse accessor. For example, if a user doesn’t have a
supervisor designated by MySpecialUser:
try:
    user.supervisor_of
except User.supervisor_of.RelatedObjectDoesNotExist:
Additionally, OneToOneField accepts all of the extra arguments
accepted by ForeignKey, plus one extra argument:
OneToOneField.parent_link¶
When True and used in a model which inherits from another
concrete model, indicates that this field should be used as the
link back to the parent class, rather than the extra
OneToOneField which would normally be implicitly created by
subclassing.
See One-to-one relationships for usage
examples of OneToOneField.
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 and querysets.
In models, a field is instantiated as a class attribute and represents a
particular table column, see Models. It has attributes
such as null and unique, and methods that Django uses to
map the field value to database-specific values.
A Field is a subclass of
RegisterLookupMixin and thus both
Transform and
Lookup can be registered on it to be used
in QuerySets (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 of Field. If you need a custom field, you can either
subclass any of the built-in fields or write a Field 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 the connection.
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
and OneToOneField that point to the Field, taking
into account the connection.
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() and get_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 returns
value if prepared=True and get_prep_value() if is
False.
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 as self.
See Converting values to Python objects for usage.
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 call super in your definition.
When saving, pre_save() and get_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 returns
get_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. for DateField.auto_now).
model_instance is the instance this field belongs to and add
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 in
self.attname (this is set up by Field).
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 in
clean().
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, the Field
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 for
ModelForm.
By default, if both form_class and choices_form_class are
None, it uses CharField. If the field has
choices and choices_form_class
isn’t specified, it uses TypedChoiceField.
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.
Field.hidden¶
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 a ForeignKey with a
related_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 is
True is ManyToManyField.
Field.many_to_one¶
Boolean flag that is True if the field has a many-to-one relation, such
as a ForeignKey; False otherwise.
Field.one_to_many¶
Boolean flag that is True if the field has a one-to-many relation, such
as a GenericRelation or the reverse of a ForeignKey; False
otherwise.
Field.one_to_one¶
Boolean flag that is True if the field has a one-to-one relation, such
as a OneToOneField; False otherwise.
Field.related_model¶
Points to the model the field relates to. For example, Author in
ForeignKey(Author, on_delete=models.CASCADE). The related_model for
a GenericForeignKey is always None.
        
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