Restricts the records to the query subject to the passed
        +restrictions+. Analog to "WHERE" in SQL. Can pass multiple
        restrictions, and can invoke this method multiple times per query.

def where(self, *custom_restrictions, **restrictions):
        """
        Restricts the records to the query subject to the passed
        +restrictions+. Analog to "WHERE" in SQL. Can pass multiple
        restrictions, and can invoke this method multiple times per query.
        """
        for attr, value in restrictions.items():
            self.where_query[attr] = value
        if custom_restrictions:
            self.custom_where.append(tuple(custom_restrictions))
        return self