我想过滤是否已经有标题URL存在于mongo数据库中
如果是，覆盖到mongo db请指导我如何过滤scrappy和mongo之间的titleURL？
items.py:

from scrapy.contrib.djangoitem import DjangoItem
from mongo_test.models import Ct
class CtItem(DjangoItem):
    django_model = Ct

蒙戈models.py:

class Ct(models.Model):   
    title       = models.CharField(max_length=100)                 
    titleURL    = models.URLField(max_length=255)   
    .....

pipeline.py ：

from mongo_test.models import Ct
class CtPipeline(object):
    def process_item(self, item, spider):
        ct = item.save(commit=False)  
        ct_exist = Ct.objects.filter()  #how to let scrapy titleURL= mongo titleURL
    if ct_exist:
       # override to mongo
    ct.save()
    return item

settings.py 在django项目中：

DATABASES = {
    'default': {
        'ENGINE': 'django_mongodb_engine',
        'NAME': 'scrapy',
    } 
}