Django Design Patterns and Best Practices - Second Edition

Avoid passing complex objects to tasks

It is easy to forget that each time we call a Celery task, the arguments get serialized before it enters the queue. Hence, it is not advisable to send a Django ORM object or any large object that might clog up the queues.

There is another good reason to avoid sending a database object. Due to the asynchronous nature of execution, the data can be outdated by the time the task has begun execution. The record might have changed or even deleted.

So, always pass a primary key or lookup value and retrieve the latest value of the object from the database. Celery documents refer to this as the responsibility of asserting that the world lies with the task. Ensure that your world is the present one, not the past. ...