Definition of a user work item index using multi map reduce

UserWorkItemIndex.cs

 public class UserWorkItemIndex : AbstractMultiMapIndexCreationTask<UserWorkItemIndex.Result>
    {
        public class Result
        {
            public string UserId { get; set; }
            public string DocumentId { get; set; }
            public int Validated { get; set; }
            public int Total { get; set; }

            public string FieldId { get; set; }
            public WorkItemStatus Status { get; set; }
        }

        public UserWorkItemIndex()
        {
            AddMap<ExtractionUser>(users => from user in users
                                            from field in user.AssignedFields
                                            select new
                                            {
                                                UserId = user.Id,
                                                FieldId = field,
                                                Status = WorkItemStatus.Ready,
                                                DocumentId = (string)null,
                                                Validated = 0,
                                                Total = 0
                                            });

            AddMap<WorkItem>(items => from item in items
                                      select new
                                        {
                                            UserId = (string)null,
                                            FieldId = item.FieldValue.FieldName,
                                            Status = item.Status,
                                            DocumentId = item.DocumentId,
                                            Validated = 0,
                                            Total = 0
                                        });

            Reduce = results => results.GroupBy(r => r.FieldId)
                .Select(g => new
                {
                    FieldId = g.Key,
                    Users = g.Where(r => r.UserId != null)
                        .Select(r => new
                        {
                            UserId = r.UserId,
                            Documents = g.Where(d => d.DocumentId != null)
                                            .Select(d => new
                                            {
                                                DocumentId = d.DocumentId,
                                                Status = d.Status
                                            })
                        })
                })
                .SelectMany(g => g.Users, (g, u) => new
                {
                    UserId = u.UserId,
                    FieldId = g.FieldId,
                    Documents = u.Documents
                })
                .SelectMany(r => r.Documents, (r, d) => new
                {
                    UserId = r.UserId,
                    FieldId = r.FieldId,
                    DocumentId = d.DocumentId,
                    Status = d.Status
                })
                .GroupBy(r => new { UserId = r.UserId, DocumentId = r.DocumentId })
                .Select(g => new
                {
                    UserId = g.Key.UserId,
                    DocumentId = g.Key.DocumentId,
                    Validated = g.Count(d => d.Status == WorkItemStatus.Validated),
                    Total = g.Count(),
                    FieldId = (string)null,
                    Status = WorkItemStatus.Ready
                });
        }