disassociating relationships

in my app, i find a bunch of users in a group with the following line
of code:

group_users = Group.find(params[:id]).users

i need to take this group and add some users to it, but i found out the
hard way that

group_users << new_user

does not work the way i want it to. instead of just adding a user to
the collection of users i have, it also adds the user to the group that
i originally pulled the users from.

What exactly are you trying to accomplish? Why would you want add a
user to your group_users list who is not a user in that group?

-- James

i basically want to email all of the users in the group + the person
who created the task + the assignee

i was just trying to add those individual users and send an email to
all of the unique users in that collection.