form_validation two is_unique

Does this not work?

PHP Code:

$this->form_validation->set_rules('GatewayId', 'GatewayId', 'is_unique[tab_expense.tab_gateway_id]|is_unique[tab_income.tab_gateway_id]'); 


i.e, just run the two rules one after another.

Alternatively the way you have done it in your second suggestion also seems fine.

Paul

PS I have not tested it but it looks like it might work.