Re: Multi-table Inheritance: How to add child to parent model?

I think the problem in the original post was making Restaurant a subclass of Place:

class Restaurant(Place):

That's why Django gave an error for the missing name and address.

With a OneToOne relation pointing from each Restaurant object to a Place object, there's no need to include those fields in Restaurant. So it's not a subclass of Place:

class Restaurant(models.Model):

(As shown in the One-to-one example. Thanks for the updated link.) 

The other alternative is to keep the subclass, and remove the OneToOneField. Then do:

for place in Place.objects.all(): 
  restaurant = Restaurant(**{ 
    'name': place.name, 
    'address': place.address, 
    'serves_hot_dogs': False, 
    'serves_pizza': True, 
  }) 
  restaurant.save() 

--Davi

On Wednesday, June 22, 2016 at 5:45:23 PM UTC-5, Malik Rumi wrote:

This thread is obviously very old, but since it helped me find the answer, I thought I would share that for the benefit of others mystified by the lack of information on https://docs.djangoproject.com/en/1.9/topics/db/models/#multi-table-inheritance.

It turns out that although Derek's link to the docs was way out of date (the page does not exist anymore) his solution was still close to correct. The full documentation can be found here: https://docs.djangoproject.com/en/1.9/topics/db/examples/one_to_one/



On Thursday, November 4, 2010 at 1:25:25 PM UTC-7, Nan wrote:

I have an existing model that I want to extend using multi-table
inheritance.  I need to create a child instance for each parent
instance in the database, but I can't figure out how.  I've scoured
google and haven't come up with anything other than Ticket #7623[1].
Here are some of the things I've tried...

Let's adapt the Place / Restaurant example from the docs:

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

class Restaurant(Place):
    place = models.OneToOneField(Place, parent_link=True,
related_name='restaurant')
    serves_hot_dogs = models.BooleanField()
    serves_pizza = models.BooleanField()

I want to do the following, in essence:

for place in Place.objects.all():
  restaurant = Restaurant(**{
    'place': place,
    'serves_hot_dogs': False,
    'serves_pizza': True,
  })
  restaurant.save()

Of course, doing this tries to also create a new Place belonging to
the new Restaurant, and throws an error because no values have been
specified for the name and address fields.  I've also tried:

for place in Place.objects.all():
  restaurant = Restaurant(**{
    'serves_hot_dogs': False,
    'serves_pizza': True,
  })
  place.restaurant = restaurant
  place.save()

This, however, doesn't create any records in the restaurant table.

Any suggestions?

[1] http://code.djangoproject.com/ticket/7623

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