gistfile1.txt

            var lookup = new Dictionary<int, Artist>();
            IEnumerable<Artist> foo =
                connection.Query<Artist, Record, Artist>(
                "SELECT * FROM dbo.Artists INNER JOIN dbo.Records ON dbo.Records.artistId = dbo.Artists.id",
                (a, r) =>
                {
                    Artist artist;
                    if (!lookup.TryGetValue(a.Id, out artist))
                    {
                        lookup.Add(a.Id, artist = a);
                    }
                    if (artist.Records == null)
                    {
                        artist.Records = new List<Record>();
                    }
                    artist.Records.Add(r);
                    return artist;
                });

            var result = lookup.Values;