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I've got a model Child inheriting from a (non abstract) model Parent. For a given instance parent of Parent, how can I know if it's a Child?

If it is,

parent.child

returns the child, but otherwise it returns a DoesNotExist exception.

Is a try/except the only way to check that?

Thanks

jul

# EDIT

I've just find the same question here: Distinguishing parent model's children with Django inheritance.

And the answer is.... 

hasattr(parent, 'child')
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3 Answers3

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Is a try/except the only way to check that?

More or less.

If you only want an existence check, you can avoid the exception by saying Child.objects.filter(parent=parent).exists(), but if you want to do something with the child if it exists, it's better to just access it directly and handle the DoesNotExist.

Pi Delport
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0

I've just find the same question here: Distinguishing parent model's children with Django inheritance.

And the answer is.... 

hasattr(parent, 'child')
Community
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jul
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-2

You could use instanceof(parent, Child). It will return True for Child instances, False for Parent instances.

Ned Batchelder
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  • (This won't work: the poster's question is about Django model inheritance, not Python inheritance.) – Pi Delport Oct 15 '10 at 17:10
  • I guess this wasn't asked for. If `child` is an instance of `Child`, then it is also stored in the `Parent` table, so the question is (if i got it right), how to determine if an object retrieved from the `Parent` table is a child... – Bernhard Vallant Oct 15 '10 at 17:11