Django change IntegerField to DecimalField on inherited model - django

Question

In Django I have 2 models that are inherited from an abstract base class. The base class has an IntegerField that I want to rename and change to DecimalField for some instances. There is a ForeignKey linking the 2 child models. I've read about model inheritance in docs, but there seems to be some constraints. What's the best way to change the IntegerField to DecimalField?
class Parent(models.Model):
intfield = models.IntegerField()
class Meta:
abstract=True
class Child1(Parent):
addedfield = models.CharField(max_length=20)
class Child2(Parent):
addedfield2 = models.DecimalField(max_digits=10, decimal_places=2)
linked = models.ForeignKey(Child1, on_delete=models.CASCADE)
class GrandChild1(Child1):
# change intfield to decimal
class GrandChild2(Child2):
# change intfield to decimal
# linked to GrandChild1 instead of Child1

Answer 1

You can use extra abstract models to alter the fields in the hierarchy:
class Parent(models.Model):
intfield = models.IntegerField()
class Meta:
abstract = True
class DescendantType1(Parent):
"""This is an abstract model that inherits from the Parent model, with the "type 1"
attributes.
"""
addedfield = models.CharField(max_length=20)
class Meta:
abstract = True
class DescendantType2(Parent):
"""This is an abstract model that inherits from the Parent model, with the "type 2"
attributes.
"""
addedfield2 = models.DecimalField(max_digits=10, decimal_places=2)
linked = models.ForeignKey(
"Child1",
on_delete=models.CASCADE,
# This is required on foreign key fields in abstract models.
# See the "Note about foreign key related names" below.
related_name="%(app_label)s_%(class)s_related",
related_query_name="%(app_label)s_%(class)ss",
)
class Meta:
abstract = True
class Child1(DescendantType1):
"""A descendant with "type 1" attributes."""
class Child2(DescendantType2):
"""A descendant with "type 2" attributes."""
class GrandChild1(DescendantType1):
intfield = models.DecimalField(...)
class GrandChild2(DescendantType2):
intfield = models.DecimalField(...)
linked = models.ForeignKey(
"GrandChild1",
on_delete=models.CASCADE,
)
Note about foreign key related names
An abstract model that has a foreign key needs to use a different related_name and related_query_name for each concrete model that inherits from it, otherwise the names for the reverse relationship would be the same for each subclass.
To handle this, django allows you to use template strings with the variables app_label and class so that the names are unique for the child model.
You can find more about this in the documentation.