Ok, so I think I can find out which is the map key column (the only column which is part of the row key but not the association key) and I managed to persist the suggested format. But when reading back I don't know that the given value actually is for the column addresses_id, so I seem not to be able to re-construct the association row in the correct form (we don't have the information about all the column names in the association/row key metadata).