# Using Celery with Django

Integrating Celery with Django allows you to handle background tasks like sending emails, processing images, or generating reports without blocking the main request-response cycle.

## 1. Installation

Install Celery and a broker interface (e.g., Redis).

```bash
pip install celery redis
```

## 2. Project Setup

You need to define the Celery instance in your Django project. Suppose your project is named `myproject`.

### Create `celery.py`

Create a file named `celery.py` inside your main project directory (next to `settings.py` and `urls.py`).

```python
# myproject/celery.py
import os
from celery import Celery

# Set the default Django settings module for the 'celery' program.
os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'myproject.settings')

app = Celery('myproject')

# Using a string here means the worker doesn't have to serialize
# the configuration object to child processes.
# - namespace='CELERY' means all celery-related configuration keys
#   should have a `CELERY_` prefix.
app.config_from_object('django.conf:settings', namespace='CELERY')

# Load task modules from all registered Django apps.
app.autodiscover_tasks()

@app.task(bind=True, ignore_result=True)
def debug_task(self):
    print(f'Request: {self.request!r}')
```

### Update `__init__.py`

To ensure the Celery app is loaded when Django starts, modify `myproject/__init__.py`.

```python
# myproject/__init__.py
from .celery import app as celery_app

__all__ = ('celery_app',)
```

## 3. Configuration

Add Celery configuration to your `settings.py`.

```python
# settings.py

# Celery Configuration Options
CELERY_BROKER_URL = 'redis://localhost:6379/0'
CELERY_RESULT_BACKEND = 'redis://localhost:6379/0'
CELERY_ACCEPT_CONTENT = ['application/json']
CELERY_TASK_SERIALIZER = 'json'
CELERY_RESULT_SERIALIZER = 'json'
CELERY_TIMEZONE = 'UTC'
```

## 4. Creating Tasks

You can define tasks in a `tasks.py` file inside any of your Django apps. Use the `@shared_task` decorator so your apps don't need to import the specific Celery app instance.

```python
# myapp/tasks.py
from celery import shared_task

@shared_task
def add(x, y):
    return x + y

@shared_task
def send_welcome_email(user_id):
    # Logic to send email
    return f"Email sent to user {user_id}"
```

## 5. Running the Worker

Open a terminal and run the Celery worker from your project root.

```bash
celery -A myproject worker -l INFO
```

*   `-A myproject`: Specifies the Django project name (where `celery.py` is located).
*   `-l INFO`: Sets the logging level.

## 6. Django Database Access

Celery tasks can interact with Django models just like regular views.

```python
from celery import shared_task
from .models import User

@shared_task
def count_users():
    return User.objects.count()
```

*Note: Be careful passing model instances to tasks. It is better to pass the primary key (ID) and fetch the object inside the task to avoid race conditions and serialization issues.*

[[programming/python/celery]] [[programming/python/django]]