Set Django IntegerField by choices=... name

When you have a model field with a choices option you tend to have some magic values associated with human readable names. Is there in Django a convenient way to set these fields by the human readable name instead of the value?

Consider this model:

class Thing(models.Model):
  PRIORITIES = (
    (0, 'Low'),
    (1, 'Normal'),
    (2, 'High'),
  )

  priority = models.IntegerField(default=0, choices=PRIORITIES)

At some point we have a Thing instance and we want to set its priority. Obviously you could do,

thing.priority = 1

But that forces you to memorize the Value-Name mapping of PRIORITIES. This doesn't work:

thing.priority = 'Normal' # Throws ValueError on .save()

Currently I have this silly workaround:

thing.priority = dict((key,value) for (value,key) in Thing.PRIORITIES)['Normal']

but that's clunky. Given how common this scenario could be I was wondering if anyone had a better solution. Is there some field method for setting fields by choice name which I totally overlooked?

Do as seen here. Then you can use a word that represents the proper integer.

Like so:

LOW = 0
NORMAL = 1
HIGH = 2
STATUS_CHOICES = (
    (LOW, 'Low'),
    (NORMAL, 'Normal'),
    (HIGH, 'High'),
)

Then they are still integers in the DB.

Usage would be thing.priority = Thing.NORMAL

As of Django 3.0, you can use:

class ThingPriority(models.IntegerChoices):
    LOW = 0, 'Low'
    NORMAL = 1, 'Normal'
    HIGH = 2, 'High'


class Thing(models.Model):
    priority = models.IntegerField(default=ThingPriority.LOW, choices=ThingPriority.choices)

# then in your code
thing = get_my_thing()
thing.priority = ThingPriority.HIGH

I'd probably set up the reverse-lookup dict once and for all, but if I hadn't I'd just use:

thing.priority = next(value for value, name in Thing.PRIORITIES
                      if name=='Normal')

which seems simpler than building the dict on the fly just to toss it away again;-).

Here's a field type I wrote a few minutes ago that I think does what you want. Its constructor requires an argument 'choices', which may be either a tuple of 2-tuples in the same format as the choices option to IntegerField, or instead a simple list of names (ie ChoiceField(('Low', 'Normal', 'High'), default='Low') ). The class takes care of the mapping from string to int for you, you never see the int.

  class ChoiceField(models.IntegerField):
    def __init__(self, choices, **kwargs):
        if not hasattr(choices[0],'__iter__'):
            choices = zip(range(len(choices)), choices)

        self.val2choice = dict(choices)
        self.choice2val = dict((v,k) for k,v in choices)

        kwargs['choices'] = choices
        super(models.IntegerField, self).__init__(**kwargs)

    def to_python(self, value):
        return self.val2choice[value]

    def get_db_prep_value(self, choice):
        return self.choice2val[choice]

I appreciate the constant defining way but I believe Enum type is far best for this task. They can represent integer and a string for an item in the same time, while keeping your code more readable.

Enums were introduced to Python in version 3.4. If you are using any lower (such as v2.x) you can still have it by installing the backported package: pip install enum34.

# myapp/fields.py
from enum import Enum    


class ChoiceEnum(Enum):

    @classmethod
    def choices(cls):
        choices = list()

        # Loop thru defined enums
        for item in cls:
            choices.append((item.value, item.name))

        # return as tuple
        return tuple(choices)

    def __str__(self):
        return self.name

    def __int__(self):
        return self.value


class Language(ChoiceEnum):
    Python = 1
    Ruby = 2
    Java = 3
    PHP = 4
    Cpp = 5

# Uh oh
Language.Cpp._name_ = 'C++'

This is pretty much all. You can inherit the ChoiceEnum to create your own definitions and use them in a model definition like:

from django.db import models
from myapp.fields import Language

class MyModel(models.Model):
    language = models.IntegerField(choices=Language.choices(), default=int(Language.Python))
    # ...

Querying is icing on the cake as you may guess:

MyModel.objects.filter(language=int(Language.Ruby))
# or if you don't prefer `__int__` method..
MyModel.objects.filter(language=Language.Ruby.value)

Representing them in string is also made easy:

# Get the enum item
lang = Language(some_instance.language)

print(str(lang))
# or if you don't prefer `__str__` method..
print(lang.name)

# Same as get_FOO_display
lang.name == some_instance.get_language_display()