异步任务利器Celery(二)在django项目中使用Celery

Celery 4.0支持django1.8及以上的版本，低于1.8的项目使用Celery 3.1。

一个django项目的组织如下：

- proj/
  - manage.py
  - proj/
    - __init__.py
    - settings.py
    - urls.py

首先建立proj/proj/celery.py文件：

from __future__ import absolute_import, unicode_literals
import os
from celery import Celery

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

app = Celery('proj')

# 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 app configs.
app.autodiscover_tasks()

@app.task(bind=True)
def debug_task(self):
    print('Request: {0!r}'.format(self.request))

然后要保证django项目启动时上述的app被载入，修改proj/proj/__init__.py文件：

from __future__ import absolute_import, unicode_literals

# This will make sure the app is always imported when
# Django starts so that shared_task will use this app.
from .celery import app as celery_app

__all__ = ['celery_app']

现在就可以在INSTALLED_APPS中的app下建立tasks.py文件啦：

- app1/
    - tasks.py
    - models.py
- app2/
    - tasks.py
    - models.py

比如：

# Create your tasks here
from __future__ import absolute_import, unicode_literals
from celery import shared_task

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

@shared_task
def mul(x, y):
    return x * y

@shared_task
def xsum(numbers):
    return sum(numbers)

在views中调用这些tasks即可异步运行。

如果使用Redis作为broker，在settings.py中添加：

CELERY_BROKER_URL = 'redis://localhost:6379/0'

可以使用Django ORM/Cache作为储存backend。

下载库：

$ pip install django-celery-results

设定settings.py：

INSTALLED_APPS = (
    ...,
    'django_celery_results',
)

建立数据表：

$ python manage.py migrate django_celery_results

在settings.py中添加Celery设置：

CELERY_RESULT_BACKEND = 'django-db'

或者

CELERY_RESULT_BACKEND = 'django-cache'

区别在于使用django ORM还是使用django缓存系统。

启动：

$ celery -A proj worker -l info

可以在python manage.py shell中调用：

$ python manage.py shell
Python 2.7.12 (default, Nov 19 2016, 06:48:10)
[GCC 5.4.0 20160609] on linux2
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> from app1.tasks import add
>>> add.delay(3,4)
<AsyncResult: a9abab6d-b7a9-47e6-8c09-ec284948449f>

celery日志：

[2017-09-14 00:09:41,432: INFO/ForkPoolWorker-1] Task urldata.tasks.add[38af760e-ed6c-48f8-b77c-d67bade8d6b8] succeeded in 0.00782653002534s: 7

官方一个完整的例子：https://github.com/celery/celery/tree/master/examples/django/

官方文档还有一个异步审查用户上传评论的例子。

blog/models.py：

from django.db import models
from django.utils.translation import ugettext_lazy as _

class Comment(models.Model):
    name = models.CharField(_('name'), max_length=64)
    email_address = models.EmailField(_('email address'))
    homepage = models.URLField(_('home page'),
                               blank=True, verify_exists=False)
    comment = models.TextField(_('comment'))
    pub_date = models.DateTimeField(_('Published date'),
                                    editable=False, auto_add_now=True)
    is_spam = models.BooleanField(_('spam?'),
                                  default=False, editable=False)

    class Meta:
        verbose_name = _('comment')
        verbose_name_plural = _('comments')

在views中先保存评论，同时调用celery异步审核。

blog/views.py：

from django import forms
from django.http import HttpResponseRedirect
from django.template.context import RequestContext
from django.shortcuts import get_object_or_404, render_to_response

from blog import tasks
from blog.models import Comment

class CommentForm(forms.ModelForm):

    class Meta:
        model = Comment

def add_comment(request, slug, template_name='comments/create.html'):
    post = get_object_or_404(Entry, slug=slug)
    remote_addr = request.META.get('REMOTE_ADDR')

    if request.method == 'post':
        form = CommentForm(request.POST, request.FILES)
        if form.is_valid():
            comment = form.save()
            # Check spam asynchronously.
            tasks.spam_filter.delay(comment_id=comment.id,
                                    remote_addr=remote_addr)
            return HttpResponseRedirect(post.get_absolute_url())
    else:
        form = CommentForm()

    context = RequestContext(request, {'form': form})
    return render_to_response(template_name, context_instance=context)

tasks如下：

blog/tasks.py

from celery import Celery

from akismet import Akismet

from django.core.exceptions import ImproperlyConfigured
from django.contrib.sites.models import Site

from blog.models import Comment

app = Celery(broker='amqp://')

@app.task
def spam_filter(comment_id, remote_addr=None):
    logger = spam_filter.get_logger()
    logger.info('Running spam filter for comment %s', comment_id)

    comment = Comment.objects.get(pk=comment_id)
    current_domain = Site.objects.get_current().domain
    akismet = Akismet(settings.AKISMET_KEY, 'http://{0}'.format(domain))
    if not akismet.verify_key():
        raise ImproperlyConfigured('Invalid AKISMET_KEY')

    is_spam = akismet.comment_check(user_ip=remote_addr,
                        comment_content=comment.comment,
                        comment_author=comment.name,
                        comment_author_email=comment.email_address)
    if is_spam:
        comment.is_spam = True
        comment.save()

    return is_spam