RavenDB Multi Map reduce出现问题

我是Raven的新手，所以我甚至不确定我在这里是否采取了正确的方法。我需要生成一个项目列表，这些项目的属性是从单独的文档中提取的。。。本质上是一个JOIN。

假设我有这些对象：

public class Merchant
{
   public string Id {get;set;}
   public string MerchantName {get;set;}
}
public class Location
{
   public string Id {get;set;}
   public string MerchantId {get;set;}
   public string City {get;set;}
}
public class Item
{
   public string Id {get;set;}
   public string MerchantId {get;set;}
   public string ItemName {get;set;}
}

我需要将Reduce（我认为）映射到MerchantItem 列表中

public class MerchantItem
{
   public string ItemId {get;set;}
   public string MerchantId {get;set;{
   public string LocationId {get;set;}
   public string ItemName {get;set;}
   public string City {get;set;}
   public string MerchantName {get;set;}
}

这是我的（非工作）多地图减少：

AddMap<Merchant>(merchants => from m in merchants
                              select new
                              {
                               ItemId = (string)null,
                               MerchantId = m.Id,
                               LocationId = (string)null,
                               ItemName = (string)null,
                               City = (string)null,
                               MerchantName = m.Name
                              });
AddMap<Location>(locations => from l in locations
                              select new
                              {
                               ItemId = (string)null,
                               MerchantId = l.MerchantId,
                               LocationId = l.Id,
                               ItemName = (string)null,
                               City = l.City,
                               MerchantName = (string)null
                              });
AddMap<Item>(items=> from i in items
                              select new
                              {
                               ItemId = i.Id,
                               MerchantId = i.MerchantId,
                               LocationId = (string)null,
                               ItemName = i.ItemName,
                               City = (string)null,
                               MerchantName = (string)null
                              });
Reduce = results => from r in results
                    group result by r.LocationId
                    into g
                    select new
                    {
                     ItemId = g.Select(x => x.ItemId),
                     MerchantId = g.Select(x => x.MerchantId),
                     LocationId =  g.Key,
                     ItemName = g.Select(x => x.ItemName ).Where(x => x != null).FirstOrDefault(),
                     City =  g.Select(x => x.City ).Where(x => x != null).FirstOrDefault(),
                     MerchantName = g.Select(x => x.MerchantName ).Where(x => x != null).FirstOrDefault()
                     });

这个想法是，我需要数据库中的每个项目和位置都有一个MerchantItem。在SQL中，我们只讨论了几个联接，但我完全不知道如何在Raven中做到这一点。