Choices for Django model fields as enumeration

• Specialized enum types
• Specialized model fields
• Accessible in templates

• Python >= 3.5
• Django >= 1.11.29

1. Run pip install django-echoices.

1. Make sure pandoc is installed
2. Run ./pypi_packager.sh
3. Run pip install dist/django_echoices-x.y.z-[...].wheel, where x.y.z must be replaced by the actual version number and [...] depends on your packaging configuration

First, define your choices enumeration (in your models.py for example):

from echoices.enums import EChoice

class EStates(EChoice):
    # format is: (value -> char or str or int, label -> str)
    CREATED = ('c', 'Created')
    SUBMITTED = ('s', 'Submitted')

Then, either use a regular model field:

from django.db import models

class MyModel(models.Model):
    state = models.CharField(max_length=EStates.max_value_length(),
                             choices=EStates.choices(),
                             default=EStates.CREATED.value)

Note: If your value is an int, you can use models.IntegerField instead.

You can also use specialized field. Using such a field, you will then only handle Echoice instances.

from django.db import models
from echoices.fields import make_echoicefield

class MyModel(models.Model):
    # `max_length` is set automatically
    state = make_echoicefield(EStates, default=EStates.CREATED)

Note: MyModel.state will be Estates instance stored in a EStatesField field. See documentation for more details.

WARNING: requires special handling of migrations. Read more in the documentation.

You can add your own fields to the value and label ones. To do so, you have to override the init() and your signature must look like: self, value, label, *args where you replace *args with your own positional arguments, as you would do when defining a custom Enum. Do not call the super().init(), as value and label are already set internally by EChoice.

As when dealing with a derived Enum, you can also add your own methods.

from echoices.enums import EChoice

class EMyChoices(EChoice):
    """Another variant of EChoice with additionnal content"""

    MY_CHOICE = (1, 'First choice', 'my additional value')

    def __init__(self, value, label, my_arg):
        self.my_arg = my_arg
        # Note: super().__init__() shall *not* be called!

    def show_myarg(self):
        """Used as: EMyChoices.MY_CHOICE.show_myarg()"""
        print(self.my_arg)

    @classmethod
    def show_all(cls):
        """Used as: EMyChoices.show_all()"""
        print(", ".join([e.my_arg for e in list(cls)]))

Assume a Context(dict(estates=myapp.models.EStates)) is provided to the following templates.

• Fields of the EChoice can be accessed in the templates as:

  {{ estates.CREATED.value }}
  {{ estates.CREATED.label }}
  

• EChoice can also be enumerated:

  {% for state in estates %}
      {{ state.value }}
      {{ state.label }}
  {% endfor %}
  

Base enum type. Each enum element is a tuple (value, label), where [t]he first element in each tuple is the actual value to be set on the model, and the second element is the human-readable name  ^doc. Values must be unique. Can be derived for further customization.

Supports ordering of elements. EOrderedChoice.choices() takes an extra optional argument, order, which supports three values: 'sorted', 'reverse' or 'natural' (default). If sorted, the choices are ordered according to their value. If reverse, the choices are ordered according to their value as if each comparison were reversed. If natural, the order is the one used when instantiating the enumeration.

Generates auto-incremented numeric values. It's then used like:

from echoices.enums import EAutoChoice

class EStates(EAutoChoice):
    # format is: label -> str
    CREATED = 'Created'
    SUBMITTED = 'Submitted'

• EChoice.__getitem__(), such that you can retrieve an EChoice instance using EChoice['my_value']

• choices() generates the choices as expected by a Django model field
• max_value_length() returns the max length for the Django model field, if the values are strings
• values() returns a list of all the values
• get(value, default=None) returns the EChoice instance having that value, else returns the default

Deal directly with the enum instances instead of their DB storage value. The specialized field will be derived from a models.Field subclass, the internal representation is deduced from the value type. So for example if the values are strings, then the the EChoiceField will subclass models.CharField; and if the values are integers then it will be models.IntegerField. Actually supports str, int, float and (non-null) bool as enum values.

make_echoicefield() will return an instance of EChoiceField which subclasses a field type from models.CharField. The exact name of the field type will be MyEnumNameField in Django >= 1.9, note the suffixed 'Field'. For earlier versions of Django, it will be EChoiceField.

Thus, MyModel.my_echoice_field will be an EChoice instance stored in an EChoiceField field.

Since the field is generated with the help of a factory function, it does not exist as is as a field class in echoices.fields. But, when generating a migration file, Django will set the class of the field as the resulting class from make_echoicefield(), which does not exist in echoices.fields. This will cause the Django server to crash, as an AttributeError: module 'echoices.fields' has no attribute 'MyEnumNameField' exception will be raised.

To prevent this, you have to edit the migration file and replace the instantiation of the non-existing class with a call to make_echoicefield(), with the same parameters as when defining the field in your model.

For example, assume you have the following model defined in models.py:

from django.db import models
from echoices.fields import make_echoicefield

class MyModel(models.Model):
    state = make_echoicefield(EStates, default=EStates.CREATED)

Then you would replace the generated field instantiation statement in migrations/0001_initial.py

migrations.CreateModel(
    name='MyModel',
    fields=[
        # Replace the statement below
        ('state', echoices.fields.EStatesField(
                        echoices=app.models.EStates,
                        default=app.models.EStates(1))
        ),
    ],

with

        ('state', echoices.fields.make_echoicefield(
                        echoices=app.models.EStates,
                        default=app.models.EStates.CREATED)
        ),

Similar to previous fields, but supports multiple values to be selected. Not yet implemented.

Assume a Context(dict(estates=myapp.models.EStates)) is provided to the following templates.

• Fields of the EChoice can be accessed in the templates as:

  {{ estates.CREATED.value }}
  {{ estates.CREATED.label }}
  

• EChoice can also be enumerated:

  {% for state in estates %}
      {{ state.value }}
      {{ state.label }}
  {% endfor %}