如何在RavenDB多映射索引中进行嵌套分组

我的RavenDB数据库中有两个不同的文档集合 - 团队和比赛。文档如下所示：

public class Team {
    public string Id { get; set; }
    public string Name { get; set; }
    public int LeaguePosition { get; set; }
}
public class Match {
    public string Id { get; set; }
    public string HomeTeamName { get; set; }
    public string AwayTeamName { get; set; }
    public DateTime StartTime { get; set; }
}

所以基本上我有球队和这些球队之间的比赛。但是，对于某些操作，我需要从数据库中获取一个如下所示的实体：

public class MatchWithExtraData {
    public string Id { get; set; } // Id from the match document.
    public string HomeTeamId { get; set; }
    public string HomeTeamName { get; set; }
    public int HomeTeamPosition { get; set; }
    public string AwayTeamId { get; set; }
    public string AwayTeamName { get; set; }
    public int AwayTeamPosition { get; set; }
    public DateTime? StartTime { get; set; }
}

我想要的是比赛文件，但有额外的字段用于主客队的ID和联赛位置。基本上，将主队和客队名称上的比赛文件与两个球队文件连接起来，一个用于主队，一个用于客队。我认为多映射/减少索引应该可以解决问题，所以我从以下索引开始：

public class MatchWithExtraDataIndex: AbstractMultiMapIndexCreationTask<MatchWithExtraData> {
    public MatchWithExtraData() {
        AddMap<Team>(
            teams => from team in teams
                     select new {
                         Id = (string)null,
                         HomeTeamId = team.Id,
                         HomeTeamName = team.Name,
                         HomeTeamPosition = team.LeaguePosition,
                         AwayTeamId = team.Id,
                         AwayTeamName = team.Name,
                         AwayTeamPosition = team.LeaguePosition,
                         StartTime = (DateTime?)null
                     }
        );
        AddMap<Match>(
            matches => from match in matches
                       select new {
                           Id = match.Id,
                           HomeTeamId = (string)null,
                           HomeTeamName = match.HomeTeamName,
                           HomeTeamPosition = 0,
                           AwayTeamId = (string)null,
                           AwayTeamName = match.AwayTeamName,
                           AwayTeamPosition = 0,
                           StartTime = match.StartTime
                       }
        );
        Reduce = results => from result in results
                            // NOW WHAT?
    }
}

减少部分是我无法弄清楚的部分，因为每场比赛都有两支球队。我想我需要先在HomeTeamName上做一个嵌套的组，然后在AwayTeamName上，但我不知道该怎么做。

也许这更像是一个LINQ问题，而不是RavenDB问题。但是，这样一个按语句嵌套的组会是什么样子呢？或者可以用另一种方式完成？