MultiMap Index - RavenDb

gistfile1.cs

public class GroupsIndex_ByAccount : AbstractMultiMapIndexCreationTask<GroupsIndex_ByAccount.ReduceResult>
    {
        public class ReduceResult
        {
            public string Id { get; set; }
            public string GroupId { get; set; }
            public string Name { get; set; }

            public string AccountId { get; set; }
            public DateTimeOffset DateJoined { get; set; }
            public DateTimeOffset LastVisitedDate { get; set; }

            public int MemberCount { get; set; }
        }

        public GroupsIndex_ByAccount()
        {
            AddMap<Group>(groups => from grp in groups
                                        select new
                                                   {
                                                        grp.Id,
                                                        GroupId = grp.Id,
                                                        grp.Name,
                                                        AccountId = (string)null,
                                                        DateJoined = (object)null,
                                                        LastVisitedDate = (object)null,
                                                        MemberCount = 0
                                                   });

            AddMap<GroupMember>(members => from member in members
                                           select new
                                           {
                                               Id = member.GroupId,
                                               GroupId = member.GroupId,
                                               Name = (string)null,
                                               AccountId = member.AccountId,
                                               DateJoined = member.DateJoined,
                                               LastVisitedDate = member.LastVisitedDate,
                                               MemberCount = 0
                                           });

            AddMap<GroupMember>(members => from member in members
                                           select new
                                                      {
                                                          Id = member.GroupId,
                                                          GroupId = member.GroupId,
                                                          Name = (string)null]=
                                                          AccountId = (string)null,
                                                          DateJoined = (object)null,
                                                          LastVisitedDate = (object)null,
                                                          MemberCount = 1
                                                      });


            Reduce = results => from result in results
                                group result by result.Id
                                    into g
                                    select new
                                    {
                                        Id = g.Key,
                                        GroupId = g.Select(x => x.GroupId).Where(x => x != null).FirstOrDefault(),
                                        Name = g.Select(x => x.Name).Where(x => x != null).FirstOrDefault(),
                                        AccountId = g.Select(x => x.AccountId).Where(x => x != null).FirstOrDefault(),
                                        DateJoined = g.Select(x => x.DateJoined).Where(x => x != null).FirstOrDefault(),
                                        LastVisitedDate = g.Select(x => x.LastVisitedDate).Where(x => x != null).FirstOrDefault(),
                                        MemberCount = g.Sum(x => x.MemberCount)
                                    };
        }
    }