search for: has_an_belongs_to_mani

We have tables Users and Communities linked by has_an_belongs_to_many. The join table Communities_Users has additional fields [ is_active, is_blocked, join_date] etc. These are populated using @user.push_with_attributes(:is_active => true,...). Later on how do we update or retrieve the attributes in the link table for a given user or a community with doing it explicitly using SQL? Thanks,