Raven multi map index

gistfile1.cs

    public class Vacancies_SummaryWithApplicationCount : AbstractMultiMapIndexCreationTask<VacancySummary>
    {
        public Vacancies_SummaryWithApplicationCount()
        {
            AddMap<Vacancy>(vacancies => from v in vacancies
                                         select new
                                         {
                                             Id = v.Id,
                                             Position = v.Position,
                                             StateId = v.StateId,
                                             DateSubmitted = v.DateSubmitted,
                                             ApplicationCount = 0
                                         });

            AddMap<VacancyApplication>(applications => from a in applications
                                                       select new
                                                       {
                                                           Id = a.VacancyId,
                                                           Position = (string)null,
                                                           StateId = (string)null,
                                                           DateSubmitted = DateTime.MinValue,
                                                           ApplicationCount = 1,
                                                       });

            Reduce = results => from result in results
                                group result by result.Id into summary
                                select new
                                {
                                    Id = summary.Key,
                                    Position = summary.Select(x => x.Position).Where(x => x != null).FirstOrDefault(),
                                    StateId = summary.Select(x => x.StateId).Where(x => x != null).FirstOrDefault(),
                                    DateSubmitted = summary.Select(x => x.DateSubmitted).Where(x => x != DateTime.MinValue).FirstOrDefault(),
                                    ApplicationCount = summary.Sum(x => x.ApplicationCount)
                                };
        }
    }