Database entries added in background task don't show up on heroku - django

Question

I have a background task in my django application, which enters all the rows from a csv into one of the tables in my database. I pass the csv via the admin site, that creates a background task, that I can run with python manage.py process_tasks. This all works locally, but on my heroku app, for some reason it doesn't.
I thought maybe inputting data is impossible from the heroku console, but if I run python manage.py shell on the heroku console, I can input data just fine.
This is the code that inputs the data into the database:
from background_task import background
...
#background(schedule=5)
def save_course_from_df(df):
df = pandas.read_json(df)
db = 0
for index, row in df.iterrows():
print("%s percent done!" % str(db / df.shape[0]))
db += 1
values = dict(row)
values = {key: values[key] for key in values.keys()
if type(values[key]) != float or not math.isnan(values[key])}
try:
Course.objects.update_or_create(
url=row['url'],
defaults=values
)
except IntegrityError:
pass
print('done!')
I run this by opening the heroku console and running 'python manage.py process_tasks'. I get the print messages, and no error is being thrown. Still, my database doesn't change.
I expected that after the task runs I would have a full table. Instead, nothing changed.

Answer 1

It seems the problem was with my migrations. For some reason the database on the heroku app had a not null constraint for a column whose model had the null=True argument.