Model field reference

Model field reference

This document contains all the API references of Field including the field options and field types Django offers.

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. 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;” the Django convention is to use the empty string, not NULL. 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.

Supplying missing values

blank=True can be used with fields having null=False, but this will require implementing clean() on the model in order to programmatically supply any missing values.

`choices`

Field.choices[source]

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.

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.

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. 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)")

Changed in Django 5.0:

Support for using enumeration types directly in the choices was added.

`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`

New in Django 5.0.

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.

`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": "to1@example.com"}

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.

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.

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 to EXTENDED.

`DateField`

class DateField(auto_now=False , auto_now_add=False , **options)[source]

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.

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`

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.

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`

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.

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`

class EmailField(max_length=254 , **options)[source]

A CharField that checks that the value is a valid email address using EmailValidator.

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