kombu.exceptions.EncodeError: User is not JSON serializable

Question

I have django 1.11.5 app with celery 4.1.0 and I recived all the time:

kombu.exceptions.EncodeError: <User: testuser> is not JSON serializable

my settings.py:

CELERY_BROKER_URL = 'amqp://localhost'
CELERY_RESULT_BACKEND = 'amqp://localhost'
CELERY_ACCEPT_CONTENT = ['application/json']
CELERY_RESULT_SERIALIZER = 'json'
CELERY_TASK_SERIALIZER = 'json'
CELERY_TIMEZONE = 'Asia/Makassar'
CELERY_BEAT_SCHEDULE = {}

tasks.py

from __future__ import absolute_import, unicode_literals
from celery import task
from django.contrib.auth.models import User


@task(serializer='json')
def task_number_one():
    user = User.objects.create(username="testuser", email="[email protected]", password="pass")
    return user

I call task in the view:

def form_valid(self, form):
    form.instance.user = self.request.user
    task_number_one.delay()
    return super().form_valid(form)

Answer 1

This is because you are using the JSON serializer for task serialization (as indicated by the setting CELERY_TASK_SERIALIZER = 'json'), but you are trying to return a model instance (which cannot be serialized into JSON).

You have two options:

1) Don't pass the instance, pass the primary key of the instance and then look up the object inside your task.

2) Use the pickle task serializer instead. This will allow you to pass objects as arguments to your tasks and return them, but comes with it's own security concerns.