Django: Set all foreign keys to None to prevent cascade deletions

gistfile1.py

from django.db.models import get_models, get_app

MY_APPS = ('foo', 'bar')

# get all the models
models = []
for app in MY_APPS:
    try:
        models += get_models(app_mod=get_app(app))
    except ImproperlyConfigured:
        # app is missing a models.py
        pass

# set all foreign keys to None to prevent cascade deletions
for model in models:
    app_model = '{}.{}'.format(model._meta.app_label, model._meta.object_name)
    fk_field_names = [
        field.name
        for field in model._meta.fields
        if isinstance(field, ForeignKey)
    ]
    for fk_field_name in fk_field_names:
        model.objects.all().update(**{fk_field_name: None})