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from twisted.internet.threads import deferToThread
#from scrapy.utils.serialize import ScrapyJSONEncoder
from pymongo import MongoClient
from pymongo.errors import DuplicateKeyError
from scrapy.exceptions import DropItem


class MongoPipeline(object):

    """Pushes scraped data in to mongodb"""

    def __init__(self, host, port):
        client = MongoClient()
        db = client.demo # mongodb database
        self.demo_items = db.items # mongodb database collection
        
        # Assuming title field is unique to drop duplicates
        self.demo_items.ensure_index([('title', 1)], unique=True)

    @classmethod
    def from_settings(cls, settings):
        host = settings.get('MONGO_DB_HOST', '127.0.0.1')
        port = settings.get('MONGO_DB_PORT', 27017)
        return cls(host, port)
        
    def process_item(self, item, spider):
      """Run the save the save item in a thread and return the result as a Deferred."""
      
        return deferToThread(self._process_item, item)

    def _process_item(self, item):
        """Save item to mongodb"""
        
        data = {'title': item.get('title', ''),
                'link': item.get('link', ''),
                'content': item.get('content', '')
                }
        try:
            if self.demo_items.insert(data):
                return item
            return None
        except DuplicateKeyError:
            raise DropItem("Item already exist %s" % item)