Question

I am trying to design an abstract model that contains a field. Subclassed models will have this field, but they will be of various field types.

Example

class AbsModel(models.Model):
    data = models.??? #I want subclasses to choose this

    def __unicode__(self):
        return data.__str__()

    class Meta:
        abstract = True

class TimeModel(AbsModel):
    data = models.TimeField()
    ...

class CharModel(AbsModel):
    data = models.CharField(...)
    ...

I am looking for a way to enforce the existence of the data field so I can write unicode once for all objects.

If this isn’t possible, how can I refer to the “data” field of the subclass when calling the super class’s unicode

I have a feeling this second question has an obvious answer I am missing.

Answer 1

It’s not possible to override a superclass field where the field is of type models.Field.

https://docs.djangoproject.com/en/1.4/topics/db/models/#field-name-hiding-is-not-permitted

You can get round this by defining a field of another type in the superclass, and then overriding it in the child (perhaps include a __str__() method just in case the data field isn’t overriden).

from django.db import models


class AbsDataField:
    def __str__(self):
        return "undefined"

class AbsModel(models.Model):
    data = AbsDataField

    def __unicode__(self):
        return self.data.__str__()

    class Meta:
        abstract = True

class TimeModel(AbsModel):
    data = models.TimeField()
    #...

class CharModel(AbsModel):
    data = models.CharField(max_length=32)
    #...