Thanks for your response.
Your second solution is the best for my case but I still have some difficulties.
I load my main gridview to display all users :
radGridViewUserManagement.DataSource = _entities.T_USER.Local.ToBindingList();
It works fine, I can insert/update/delete rows and save to my database with _entities.SaveChanges();
When I handle the CurrentRowChanged event :
private void radGridViewUserManagement_CurrentRowChanged(object sender, CurrentRowChangedEventArgs e)
if (e.CurrentRow != null && e.CurrentRow is GridViewDataRowInfo)
currentUser = (T_USER) radGridViewUserManagement.CurrentRow.DataBoundItem;
radGridViewSelectedGroups.DataSource = currentUser.T_GROUP.ToList();
I can display my current user Groups, but the view is never updated if I add some groups programmatically with currentUser.T_GROUP.Add(testGroup);
I think my problem is the using of ToList() function when I set the DataSource.
I tried many things but I cannot update the radGridViewSelectedGroups.
Thanks for your help Hristo