clear data just for one app
do it after dump all data for backup reason
python manage.py migrate <app> zero # clear data and delete table
python manage.py migrate <app> # migrate again
invalidate all cache # in case of using cacheops
in case of migration conflict or database errors, use following code to clear data
from django.apps import apps
my_app = apps.get_app_config('my_app_name')
my_models = my_app.get_models()
for model in my_models:
model.objects.all().delete()