How can I create an inherited django model instance from an existing base model instance?

Question

I have two django models like these:

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()

I had previously created a Place instance, like this:

sixth_ave_street_vendor = Place(name='Bobby Hotdogs', address='6th Ave')
sixth_ave_street_vendor.save()

Now bobby has upgraded his street vendor to a restaurant. How can I do that in my code?! Why this code doesn't work:

sixth_ave_restaurant = Restaurant(place=sixth_ave_street_vendor,
                                  serves_hot_dogs=True,
                                  serves_pizza=True)
sixth_ave_restaurant.save()

Reza Mohammadi · Accepted Answer · 2012-12-31 13:11:31Z

5

Here is my workaround:

sixth_ave_restaurant = Restaurant(place_ptr=sixth_ave_street_vendor,
                                  serves_hot_dogs=True,
                                  serves_pizza=True)
sixth_ave_restaurant.save_base(raw=True)

And if you want to do something else with sixth_ave_restaurant, you should get it again, because its id is not assigned yet, as it gets assigned after normal save():

sixth_ave_restaurant = Restaurant.objects.get(id=sixth_ave_street_vendor.id)

edited Dec 31, 2012 at 13:11

answered Dec 25, 2012 at 23:38

Reza Mohammadi

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Comments

Fatih Erikli · Accepted Answer · 2012-12-25 22:56:32Z

3

You should use place_ptr instead of place.

restaurant = Restaurant.objects.create(place_ptr=sixth_ave_street_vendor,
                                       serves_hot_dogs=True, serves_pizza=True)

answered Dec 25, 2012 at 22:56

Fatih Erikli

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3 Comments

Reza Mohammadi Over a year ago

I Set both place_ptr and place_ptr_id, but django still tries to insert a new Place :(

Aamir Rind Over a year ago

@RezaMohammadi that might be because sixth_ave_street_vendor is not yet saved, and looking into your code you haven't called the save method sixth_ave_street_vendor.save()

Fatih Erikli Over a year ago

Here is another way: Create a model that called BasePlace, and extend the other models with that model.

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