Django - Performing a task through celery from a model

Question

In my models.py:

from django.db import models from core import tasks class Image(models.Model): image = models.ImageField(upload_to='images/orig') thumbnail = models.ImageField(upload_to='images/thumbnails', editable=False) def save(self, *args, **kwargs): super(Image, self).save(*args, **kwargs) tasks.create_thumbnail.delay(self.id) 

In my tasks .py:

 from celery.decorators import task from core.models import Image @task() def create_thumbnail(image_id): ImageObj = Image.objects.get(id=image_id) # other stuff here 

This returns the following:

• Exception Type: ImportError
• Exception value: cannot import name tasks

The error will disappear if I comment from core.models import Image in tasks.py , however this will obviously cause a problem, since Image does not make sense here. I tried to import it inside create_thumbnail , but it still doesn't recognize Image .

I read somewhere that usually the object itself can be passed as an argument to the task, and this will solve my problem. However, one day a friend told me that it is considered best practice to send as little data as possible in a RabbitMQ message, so to achieve this I try to only pass the image ID and then return it to the task again.

1) Is what I'm trying to do is considered best practice? If so, how to do it?

2) I noticed in all the examples that I found on the Internet that they perform a task from a view and never from a model. I am trying to create a sketch whenever a new image is loaded, I do not want to call create_thumbnail in all the forms / views that I have. Any ideas on this? Does the task perform from a model that is not recommended or generally accepted?

Answer 1

1) Is what I'm trying to do is considered best practice? If so, how to do it?

Yes, passing a little information into a task is usually a good thing, as you mentioned.

2) I noticed in all the examples that I found on the Internet that they perform a task from a view and never from a model. I am trying to create a sketch whenever a new image is loaded, I do not want to call create_thumbnail in all the forms / views that I have. Any ideas on this? Does the task perform from a model that is not recommended or generally accepted?

I noticed the same thing, and I think that textbooks and documents cause tasks from their representations, because it is easier to demonstrate how everything works using simple representations than with models or forms.

To eliminate cyclical imports, you should consider how imports should occur. Typically, tasks.py will need to import a lot of things from models.py, while models.py rarely needs to know anything about tasks.py. The standard should be that models.py does not import from tasks.py. Thus, if you need to do this and call the task from the model method, make the import in the method as follows:

 from django.db import models class Image(models.Model): image = models.ImageField(upload_to='images/orig') thumbnail = models.ImageField(upload_to='images/thumbnails', editable=False) def save(self, *args, **kwargs): super(Image, self).save(*args, **kwargs) from core.tasks import create_thumbnail create_thumbnail.delay(self.id) 

Answer 2

You do not need to import the task yourself. Try using the following

 from django.db import models from celery.execute import send_task, delay_task class Image(models.Model): image = models.ImageField(upload_to='images/orig') thumbnail = models.ImageField(upload_to='images/thumbnails', editable=False) def save(self, *args, **kwargs): super(Image, self).save(*args, **kwargs) result = delay_task("task_prefix.create_thumbnail", post.id) 

Answer 3

I wonder if the problem could be circular imports ( models and tasks import each other at the top level). try moving " from core.models import Image " to create_thumbnail , i.e. changing tasks to

 from celery.decorators import task @task() def create_thumbnail(image_id): from core.models import Image ImageObj = Image.objects.get(id=image_id) # other stuff here