问题

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/

回答1:

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.

回答2:

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

回答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)

回答4:

According to your reference from https://hackernoon.com/using-enum-as-model-field-choice-in-django-92d8b97aaa63. The choices should be list of tuple, while yours will return a tuple of tuple. More over i is different from i.name. Try:

#enums.py
class TransactionType(Enum):

    IN = "IN",
    OUT = "OUT"

    @classmethod
    def choices(cls):
        return [(i, i.value) for i in cls]

来源：https://stackoverflow.com/questions/54802616/how-to-use-enums-as-a-choice-field-in-django-model

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