python 里面mongodb 去重和下载

Question

现在情况是这样，我在scrapy 里面使用mongodb 去重

def process_item(self, item, spider):

url = item['file_url']
name = item['name']

result = self.post.aggregate(
    [
        {"$group": {"_id": {"url": url, "name": name}}}
    ]
)
if result:
    pass
else:

    self.post.insert({"url": url, "name": name})
    return item

def file_path(self, request, response=None, info=None):

return request.meta.get('filename', '')

def get_media_requests(self, item, info):

file_url = item['file_url']
meta = {'filename': item['name']}
yield Request(url=file_url, meta=meta)

判重过后下载如何调用呢？