Django Abstract Class change behaviour according to actual class

Question

I think following code explains what I'm trying to do

from django.db import models


class MyBaseClass(models.Model):
    type = models.IntegerField()

    class Meta:
        abstract = True

    def save(self, *args, **kwargs):
        self.type = #What Should I write here?#
        self.type = self.class.type ?
        super().save(*args, **kwargs)


class Model1(MyBaseClass):
    TYPE = 1


class Model2(MyBaseClass):
    TYPE = 2

I want to make sure following assertions work:

instance1 = Model1.objects.create()
assert(instance1.type, 1)
instance2 = Model2.objects.create()
assert(instance1.type, 2)

How can I make this work? Thanks.

What is the use of `TYPE` here? Is this just a static aspect, or do you want to set a *default* value. If it is the former, you should *never* define a `type` column in the first place, since then the records of the two models are stored in *different* tables, so it has no use at all. — Willem Van Onsem, Jan 26 '19 at 15:17

score 1 · Accepted Answer · answered Jan 26 '19 at 15:24

Setting the default value of inherited models

If you want to set the default of the inherited models, you can monkey patch these. Like:

class Model1(MyBaseClass):
    TYPE = 1


class Model2(MyBaseClass):
    TYPE = 2

Model1._meta.get_field('type').default = Model1.TYPE
Model2._meta.get_field('type').default = Model2.TYPE

Adding a static attribute to the models

In case the .type of all Model1 objects is always 1, and for Model2 objects it is always 2, then there is no reason at all to store these types in the database. These models are stored in different tables, hence the fact that a record originates from the app_model1 table "implies" that. In that case, you thus can set a class attribute, like:

class MyBaseClass(models.Model):
    type = None

    class Meta:
        abstract = True


class Model1(MyBaseClass):
    type = 1


class Model2(MyBaseClass):
    type = 2

Very insightful comment and answer, I actually wanted to do some extra logic based on the `type`, but after sleeping on it I realized I can just put the extra logic in a function and in both .save() methods I can call it with different parameters. Your answer is still very useful. — EralpB, Jan 27 '19 at 11:36

Django Abstract Class change behaviour according to actual class

1 Answers1

Setting the default value of inherited models

Adding a static attribute to the models