Invalid initial expression type for field, expecting: Id

Question

I am getting an error on the groupId get statement. This is my first attempt to use maps. Can someone tell me what I am doing wrong?

Code:

trigger UserPublicGroupMembership on User (after insert, after update ) {

    List<GroupMember> gpMember = new list<GroupMember>();

    List<Group> pubGroup = new list<Group>([
        Select Id,Name 
        FROM Group
    ]);    
    Map<Id, Group> gmap = new Map<Id, Group>(pubGroup);

    //Put user in group if insert
    if(trigger.isInsert){
        for(User u:trigger.new){

            IF (u.UserRole.Name == 'BCS Manager'){
                gpMember.add(new GroupMember(
                    UserOrGroupId = u.Id,
                    GroupId = gmap.get('BCS Managers')
                ));
            }

            //so on and so on for all our roles. 
        }
    }

    //Check if profile or role changed, then put user in group if true
    if(trigger.isUpdate){

    }

    //Nnow that list is populated insert. 
    //Always doing an insert as system doesn't care about existing membership conflicts. 
    Insert gpMember;

}

Error Message:

Invalid initial expression type for field GroupMember.GroupId, expecting: Id

Answer 1

When you call gmap.get(...) it gives you back a Group. You need its Id instead, so use gmap.get(...).Id.

If you're not sure the record will exist, this pattern can cause a QueryException. In that case, it might be better to guard against such a case:

Group bcsGroup = gmap.get('BCS Managers');
if (bcsGroup != null)
{
    // intermediate logic
    GroupId = bcsGroup.Id
}

---

Also, note that you don't need to use so much boilerplate when performing queries. Just do:

List<Group> groups = [/*query*/];

Or if you just need the Map:

Map<Id, Group> gropus = new Map<Id, Group>([/*query*/]);