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:
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.
Choices can be any sequence object – not necessarily a list or tuple. 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. Let us create a choices field with above semester in our django project named geeksforgeeks.
Use "./manage.py sql appname" to see the SQL Django generates, manually modify it to use the ENUM type, and run it yourself.
Customize Python enum classes Python enumerations are classes. It means that you can add methods to them, or implement the dunder methods to customize their behaviors.
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
. Thelabel
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
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(self) -> YearInSchool:
# Get value from choices enum
return self.YearInSchool[self.year_in_school]
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.
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)
For django > 3.0 https://docs.djangoproject.com/en/4.0/ref/models/fields/#field-choices-enum-types
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,
)
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