[Users] grp reverse function??

[Marcello Lupo]

Hi,
there is a way to accomplish the reverse function that group module do?
As i know the group module allow me to check if a user is inside a specified 
group. How can i know in which group is a user without querying the system to 
know if the user is in all the groups one by one?
Actually i'm doing it using avpops and setting an avp that tell me which is 
the group of the user.
I was wandering if there is a more efficient (more performant) way.
Thanks,
bye,
Marcello