Move a python / django object from a parent model to a child (subclass)

Question

I am subclassing an existing model. I want many of the members of the parent class to now, instead, be members of the child class.

For example, I have a model Swallow. Now, I am making EuropeanSwallow(Swallow) and AfricanSwallow(Swallow). I want to take some but not all Swallow objects make them either EuropeanSwallow or AfricanSwallow, depending on whether they are migratory.

How can I move them?

Answer 1

I know this is much later, but I needed to do something similar and couldn't find much. I found the answer buried in some source code here, but also wrote an example class-method that would suffice.

class AfricanSwallow(Swallow):

    @classmethod
    def save_child_from_parent(cls, swallow, new_attrs):
        """
        Inputs:
        - swallow: instance of Swallow we want to create into AfricanSwallow
        - new_attrs: dictionary of new attributes for AfricanSwallow

        Adapted from: 
        https://github.com/lsaffre/lino/blob/master/lino/utils/mti.py
        """
        parent_link_field = AfricanSwallow._meta.parents.get(swallow.__class__, None)
        new_attrs[parent_link_field.name] = swallow
        for field in swallow._meta.fields:
            new_attrs[field.name] = getattr(swallow, field.name)
        s = AfricanSwallow(**new_attrs)
        s.save()
        return s

I couldn't figure out how to get my form validation to work with this method however; so it certainly could be improved more; probably means a database refactoring might be the best long-term solution...