code: def read(self):
          
          result = self.get_collection().aggregate([
              {'$match': {'_id': self._document_id}},
              {'$project': {'_value': '$' + self._path, '_id': False}}
          ])
  
          for doc in result:
              if '_value' not in doc:
                  break
  
              return doc['_value']
docs: Read the target value
          Use $project aggregate operator in order to support nested objects