In a Flask App, where should Celery be instantiated?

3
votes

I have a Flask app, which is a very basic app with a POST handler and some DB insertions. The DB insertions are set as tasks using Celery. If I put my Celery instance creation and tasks definition in tasks.py file, and call the functions from my main.py file (which also has the Flask app creation), I get an out of context error. The tasks in the tasks.py file in turn call a DB class that does the DB insertions. How do I properly create the Celery instance and make sure it has the Flask context?

This is how the structure roughly resembles:

  1. main.py = Flask app creation, routes handling and tasks.delay calls.
  2. tasks.py = Celery instance creation and task definitions.
  3. DB = Inserts.

I want everything to work in the same context.

1
pythonflaskcelerymessage-queue
These links helped me blog.miguelgrinberg.com/post/using-celery-with-flask & blog.miguelgrinberg.com/post/… – Amin Alaee

1 Answers

1
votes

The Flask docs suggest subclassing Celery's Task class and wrapping task execution in a Flask app context. So in task.py if your Flask app instance is named app and your Celery instance is named celery, you would replace celery's Task attribute with the new subclass:

TaskBase = celery.Task
class ContextTask(TaskBase):
    abstract = True
    def __call__(self, *args, **kwargs):
        with app.app_context():
            return TaskBase.__call__(self, *args, **kwargs)
celery.Task = ContextTask