def _get_collection(self, collection_name):
        """
        Get PyMongo client pointing to the current DB and the given collection.

        :return: MongoDB client of the current database and given collection.
        :raise DataSourceError
        """
        try:
            return self._database[collection_name]
        except InvalidName as ex:
            raise DataSourceError("Cannot access MongoDB collection %s!"
                                  % collection_name) from ex
        except Exception as ex:
            raise DataSourceError("Unexpected error when accessing MongoDB"
                                  "collection %s!"
                                  % collection_name) from ex
Get PyMongo client pointing to the current DB and the given collection.

        :return: MongoDB client of the current database and given collection.
        :raise DataSourceError