form validation in sign in !!

[eluser]alsemany[/eluser]
I'm using the form_validation as a part of my new project with sign up and sign in

the validation with sign up is perfect with the rule

Code:

is_unique[table.field]

but when I checked if there is any rule similar to

Code:

is_unique[table.field]

to validate the for example the username or the email with signing in I didn't found in the user guide

http://ellislab.com/codeigniter/user-gui...ation.html


is there any way to make my new validation rule to check if the login id from the database !!