Question

I want to create an index for a query, I want to return to my view a list of Audio items along with statistics for these items, which are TotalDownloads & TotalPlays.

Here are my relevant docs:

Audio
 - Id
 - ArtistName
 - Name

AudioCounter
 - AudioId
 - Type
 - DateTime

Here is my current Index:

public class AudioWithCounters : AbstractMultiMapIndexCreationTask<AudioWithCounters.AudioViewModel>
{
    public class AudioViewModel
    {
        public string Id { get; set; }
        public string ArtistName { get; set; }
        public string Name { get; set; }
        public int TotalDownloads { get; set; }
        public int TotalPlays { get; set; }
    }

    public AudioWithCounters()
    {
        AddMap<Audio>(audios => from audio in audios
                                select new
                                {
                                    Id = audio.Id,
                                    ArtistName = audio.ArtistName,
                                    Name = audio.Name,
                                    TotalDownloads = 0,
                                    TotalPlays = 0
                                });

        AddMap<AudioCounter>(counters => from counter in counters
                                         where counter.Type == Core.Enums.Audio.AudioCounterType.Download
                                select new
                                {
                                    Id = counter.AudioId,
                                    ArtistName = (string)null,
                                    Name = (string)null,
                                    TotalDownloads = 1,
                                    TotalPlays = 0
                                });

        AddMap<AudioCounter>(counters => from counter in counters
                                         where counter.Type == Core.Enums.Audio.AudioCounterType.Download
                                         select new
                                         {
                                             Id = counter.AudioId,
                                             ArtistName = (string)null,
                                             Name = (string)null,
                                             TotalDownloads = 0,
                                             TotalPlays = 1
                                         });

        Reduce = results => from result in results
                            group result by result.Id
                                into g
                                select new
                                {
                                    Id = g.Key,
                                    ArtistName = g.Select(x => x.ArtistName).Where(x => x != null).First(),
                                    Name = g.Select(x => x.Name).Where(x => x != null).First(),
                                    TotalDownloads = g.Sum(x => x.TotalDownloads),
                                    TotalPlays = g.Sum(x => x.TotalPlays)
                                };
    }
}

However, my TotalDownloads & TotalPlays are always 0 even though there should be data in there. What am I doing wrong?

Answer 1

In the reduce function, replace .First() with .FirstOrDefault(), then it works.

Besides that, there is a typo in the second map-function, because you are filtering on the same AudioCounterType.Download.