#31861: Model field for enumeration types
-------------------------------------+-------------------------------------
Reporter: George | Owner: nobody
Sakkis |
Type: New | Status: new
feature |
Component: Database | Version: 3.1
layer (models, ORM) |
Severity: Normal | Keywords: enumeration
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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The new enumeration types in Django 3.0 are a great addition and
improvement over the previous choices. On the ORM layer however, only the
enumeration values are represented, not the enumeration members. I'd like
to suggest a new `EnumField` custom field that refers to the actual
enumeration member, similar to how `ForeignKey` fields refers to the
related model object instead of its primary key (or the `to_field` in
general). Proposed usage for the
[https://docs.djangoproject.com/en/3.1/ref/models/fields/#enumeration-
types Student example]:
{{{
#!python
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.EnumField(YearInSchool,
default=YearInSchool.FRESHMAN)
def is_upperclass(self):
return self.year_in_school in {
self.YearInSchool.JUNIOR,
self.YearInSchool.SENIOR,
}
}}}
In this case, `Student.year_in_school` would be a `YearInSchool` member,
not a two-letter string.
The proposed signature is the following: `class EnumField(enum_type,
field_type=None, **options)`
- `enum_type` is the enumeration type, i.e. a `models.Choices` subclass.
- `field_type` is the underlying ORM field type, e.g. `models.CharField`
or `models.PositiveSmallIntegerField`.
- In the simplest implementation, this is a required parameter to be
provided by the caller.
- Alternatively, it could be made optional and inferred based on either
of the following:
1. a new optional `field(**options)` staticmethod on the enumeration
type, if present. For example:
{{{
#!python
class YearInSchool(models.TextChoices):
FRESHMAN = 'FR', _('Freshman')
SOPHOMORE = 'SO', _('Sophomore')
JUNIOR = 'JR', _('Junior')
SENIOR = 'SR', _('Senior')
GRADUATE = 'GR', _('Graduate')
@staticmethod
def field(**options):
options.setdefault("max_length", 2)
return models.Charfield(**options)
}}}
2. Automatically based on the type and values of the enumeration
members:
- For string values: a `CharField` with `max_length` the maximum
length of the enumeration values.
- For integer values: one of {`PositiveSmallIntegerField`,
`SmallIntegerField`, `PositiveIntegerField`, `IntegerField`,
`BigIntegerField`}, the smallest that can represent all the enumeration
values.
- And so on for other types where there is a natural python type <=>
ORM field mapping, e.g. `DateField` for date values.
- If the field type cannot be inferred, raise an appropriate
exception.
--
Ticket URL: <https://code.djangoproject.com/ticket/31861>
Django <https://code.djangoproject.com/>
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