Dynamically add celery tasks

tasks.py

## THIS IS UNTESTED

from worker.models import TaskType
from website.celery import app
import importlib

# Dynamically add registered tasks

# Celery._tasks is a task registry object
# https://github.com/celery/celery/blob/34c43244b1681a59540936748800aaa504786a35/celery/app/base.py#L162 - _tasks
# https://github.com/celery/celery/blob/524421a36dcc838a5f51e5cf122902aab774bad1/celery/app/registry.py#L22 - task registry object

# Autodiscover calls AppLoader which is a thin shell around BaseLoader
# https://github.com/celery/celery/blob/34c43244b1681a59540936748800aaa504786a35/celery/app/base.py#L341 - autodisover
# https://github.com/celery/celery/blob/34c43244b1681a59540936748800aaa504786a35/celery/loaders/base.py - base loader

# task function calls _task_from_fun, which adds tasks to registry
# https://github.com/celery/celery/blob/34c43244b1681a59540936748800aaa504786a35/celery/app/base.py#L227 - task; creates a new task
# https://github.com/celery/celery/blob/34c43244b1681a59540936748800aaa504786a35/celery/app/base.py#L269 - _task_from_fun
# task function is called as a decorator on a task function

# TL;DR
# - call app.task directly on functions you want to add

def add_tasks():
    """Grab task definitions out of database and add them to celery's registry"""
    for task in TaskType.objects.all():
        # Grab the reference to the function
        # get function from call_string
        # call string should be in the form: "module1.module2.module3.task_class"
        module_path = task.call_string.split(".")
        module = importlib.import_module(".%s" %(module_path[-2]),
                                         package=".".join(module_path[0:-2]))
        task_class = getattr(module, module_path[-1])
        
        # The execute method is the callable
        # Call the 'task' method to register
        app.task(getattr(task_class, 'execute'))