code: def get_all(self, collection_name, since=None):
          
          if since is None:
              query = {}
          else:
              query = {job.TIMEPERIOD: {'$gte': since}}
          collection = self.ds.connection(collection_name)
  
          cursor = collection.find(query)
          if cursor.count() == 0:
              raise LookupError('MongoDB has no job records in collection {0} since {1}'.format(collection_name, since))
          return [Job.from_json(document) for document in cursor]
docs: method returns all job records from a particular collection that are older than <since>