Django increment ID in each subclass model individually

Question

There is an old code with two models shown as below:

class Watermelon(models.Model):
    id = models.AutoField(primary_key=True)
    name = models.CharField(max_length=64, default='Unnamed Watermelon')
    is_allegic = models.BooleanField(default=False)
    use_by = models.DateTimeField()
    seedless = models.BooleanField(default=False)

class Pear(models.Model):
    id = models.AutoField(primary_key=True)
    name = models.CharField(max_length=64, default='Unnamed Pear')
    is_allegic = models.BooleanField(default=False)
    use_by = models.DateTimeField()
    round_shape = models.BooleanField(default=False)

Now I need a generic fruit search related functions so I am trying to use model inheritance without disturbing the original ID numbers from the old data:

class Fruit(models.Model):
    name = models.CharField(max_length=64, default='Unnamed Fruit')
    is_allegic = models.BooleanField(default=False)
    use_by = models.DateTimeField()

class Watermelon(Fruit):
    id = models.AutoField(primary_key=True)
    seedless = models.BooleanField(default=False)

class Pear(Fruit):
    id = models.AutoField(primary_key=True)
    round_shape = models.BooleanField(default=False)

And this causes the conflict for the field 'id', as django doesn't allow to override fields in the subclass models.

I also tried to add a different AutoField 'base_id' in Fruit model, since the ID in the parent model is not going to be used at all. But then I am getting "django.db.utils.ProgrammingError: relation "Fruit" already exists" error when trying to run south makemigrations.

I understand that renumbering all IDs and share them with all subclass models can solve the problem, but I try to avoid this method because those IDs are already referenced by other tables and also used by other systems.

Any advice will be appreciated.

Why do you have different models for Watermelon and Pear in the first place when almost all the fields are the same in the two? Can't you simply have a single FRUIT model and specify an attribute say Fruit_name in it.? — Ankush Raghuvanshi, Aug 03 '16 at 17:32
My question is about the old code improvement and data migration so nothing can be done for the past. The Fruit thing is just an example; the actual subclass models have more specific fields. — benny, Aug 03 '16 at 18:09

score 0 · Answer 1 · answered Aug 04 '16 at 02:47

0

It should work if you make the Fruit model abstract:

class Fruit(models.Model):
    name = models.CharField(max_length=64, default='Unnamed Fruit')
    is_allegic = models.BooleanField(default=False)
    use_by = models.DateTimeField()

    class Meta:
        abstract = True

Making it abstract means that you have to subclass it before using it. This allows you to set the primary key on the child class.

answered Aug 04 '16 at 02:47

solarissmoke

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Thanks for the answer. I need a REST based search API for the parent model Fruit, so the actual database table is needed. I try not to query individual subclass models and union results. – benny Aug 04 '16 at 14:36

Django increment ID in each subclass model individually

1 Answers1