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djangoinheritancemodel

Django model inheritance: Create a subclass using existing super class

I'm using multi-table-inheritance, and want to know how to create an inherited type from an instance of the superclass.

Using the example given in the documentation:

class Place(models.Model):
    name = models.CharField(max_length=50)
    address = models.CharField(max_length=80)

class Restaurant(Place):
    serves_hot_dogs = models.BooleanField()
    serves_pizza = models.BooleanField()

Now when you create a Restaurant, you automatically make a Place, which is fine, and the behaviour I expect and want.

But what if I make a Place, and later decide I want to convert to a specific type (like Restaurant). How do you create a Restaurant, using an existing Place?

Solution

  • Multi-table inheritance is just OneToOneField relation between Place and Restaurant.

    place = Place.objects.get(id=1)               

# Create a restaurant using existing Place   
restaurant = Resturant(place_ptr=place)
# this might be needed to not delete the data: restaurant.__dict__.update(place.__dict__)
restaurant.save()