How to use enums as a choice field in django model

I have a model class of which I want two fields to be a choice fields, so to populate those choices I am using an enum as listed below

#models.py
class Transaction(models.Model):
    trasaction_status = models.CharField(max_length=255, choices=TransactionStatus.choices())
    transaction_type = models.CharField(max_length=255, choices=TransactionType.choices())

#enums.py
class TransactionType(Enum):

    IN = "IN",
    OUT = "OUT"

    @classmethod
    def choices(cls):
        print(tuple((i.name, i.value) for i in cls))
        return tuple((i.name, i.value) for i in cls)

class TransactionStatus(Enum):

    INITIATED = "INITIATED",
    PENDING = "PENDING",
    COMPLETED = "COMPLETED",
    FAILED = "FAILED"
    ERROR = "ERROR"

    @classmethod
    def choices(cls):
        print(tuple((i.name, i.value) for i in cls))
        return tuple((i.name, i.value) for i in cls)

However, when I am trying to access this model through admin I am getting the following error :

Django Version: 1.11
Exception Type: ValueError
Exception Value:    
too many values to unpack (expected 2)

I followed two articles that described how to use enums:

https://hackernoon.com/using-enum-as-model-field-choice-in-django-92d8b97aaa63
https://blog.richard.do/2014/02/18/how-to-use-enums-for-django-field-choices/

Solution 1:

Django 3.0 has built-in support for Enums

Example:

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.choices,
        default=YearInSchool.FRESHMAN,
    )
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) two-tuple. 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. Use .choices as a suitable value to pass to choices in a field definition.

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.

For more info, check the documentation

Note:

As @Danielle Madeley pointed out, if you try to access the year_in_school attribute directly Django still returns the raw string instead of the Enum object:

>>> student.year_in_school
'FR'

What I usually do is to create a helper method that returns the Enum object:

class Student(models.Model):
    ...

    def get_year_in_school() -> YearInSchool:
        # Get value from choices enum
        return self.YearInSchool[self.year_in_school]

Solution 2:

For Django 2.x and lower:

You define an Enum by setting the various options as documented here:

class TransactionStatus(Enum):

    INITIATED = "INITIATED"
    PENDING = "PENDING"
    COMPLETED = "COMPLETED"
    FAILED = "FAILED"
    ERROR = "ERROR"

Note there are no commas! This allows you later in your code to refer to TransactionStatus.ERROR or TransactionStatus.PENDING.

The rest of your code is correct. You get the choices by creating tuples of option.name, option.value.

UPDATE: For Django 3.x and higher, use the built-in types TextChoices, IntegerChoices and Choices as described here. That way you don't have to construct the choices tuple yourself.

Solution 3:

Problem in your code is that INITIATED = "INITIATED", a comma after INITIATED option and other options. when we add comma after any string it will become a tuple. See an example below

s = 'my str'
print(type(s))
# output: str

s = 'my str',
print(type(s))
# output: tuple

models.py

class Transaction(models.Model):
    trasaction_status = models.CharField(max_length=255, choices=TransactionStatus.choices())
    transaction_type = models.CharField(max_length=255, choices=TransactionType.choices())

enums.py

class TransactionType(Enum):

    IN = "IN"
    OUT = "OUT"

    @classmethod
    def choices(cls):
        print(tuple((i.name, i.value) for i in cls))
        return tuple((i.name, i.value) for i in cls)

class TransactionStatus(Enum):

    INITIATED = "INITIATED"
    PENDING = "PENDING"
    COMPLETED = "COMPLETED"
    FAILED = "FAILED"
    ERROR = "ERROR"

    @classmethod
    def choices(cls):
        print(tuple((i.name, i.value) for i in cls))
        return tuple((i.name, i.value) for i in cls)

Solution 4:

If you are receiving this error:

'choices' must be an iterable containing (actual value, human readable name) tuples

And are using Django3, then you are probably running into the same issue I did: The "Enums" have to be embedded in the model where you are trying to use them and ca not be declared outside of the model. For example, this will not work:

class YearInSchool(models.TextChoices):
    FRESHMAN = 'FR', _('Freshman')
    SOPHOMORE = 'SO', _('Sophomore')
    JUNIOR = 'JR', _('Junior')
    SENIOR = 'SR', _('Senior')
    GRADUATE = 'GR', _('Graduate')

class Student(models.Model):
   year_in_school = models.CharField(
        max_length=2,
        choices=YearInSchool.choices,
        default=YearInSchool.FRESHMAN,
    )

Where as this example from the docs will:

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.choices,
        default=YearInSchool.FRESHMAN,
    )

Solution 5:

By the way Djanog also supports the Python 3's auto() as the Enum value. You can use the following helperclass to make your life easier.

from django.db.models.enums import TextChoices

class AutoEnumChoices(TextChoices):
    def _generate_next_value_(name, start, count, last_values):  # @NoSelf
        return name.lower()
    
    @property
    def choices(cls):  # @NoSelf
        empty = [(None, cls.__empty__)] if hasattr(cls, '__empty__') else []
        return empty + [(member.value, member.label) for member in cls]

Then use it in your choices definition:

class TransferBasicStatus(AutoEnumChoices):
    NONE = auto()
    WAITING = auto()
    PENDING = auto()
    PROGRESS = auto()
    SUCCESS = auto()
    DECLINED = auto()
    ENDED =  'ended', _('Ended - The transfer has ended with mixed states')