from django.db import models

class SortableAbstract(models.Model):

position = models.PositiveIntegerField(

default=0

)

name = models.CharField(

null=True,

blank=True,

max_length=255,

)

class Meta:

abstract = True

def __str__(self):

if not self.name:

return 'Sortable {}'.format(self.pk)

return '{}'.format(self.name)

class SortableParent(SortableAbstract):

class Meta:

abstract = False

ordering = ['position']

class SortableChild(SortableAbstract):

parent = models.ForeignKey(

SortableParent,

on_delete=models.CASCADE,

)

class Meta:

abstract = False

ordering = ['position']