1

给定这样的模型：

public class Location
{
    public int Id { get; set; }

    public string Name { get; set; }

    public Coordinates Geo { get; set; }

    public IList<Review> Reviews { get; set; }
}

public class Review
{
    public string Comment { get; set; }

    public int Rating { get; set; }
}

如何编写一个查询来返回按评级降序排序的匹配位置？

我有一个索引，可让我查询地理点周围一定半径内的位置：

public class Locations_ByCoordinates : AbstractIndexCreationTask<Location>
{
    public Locations_ByCoordinates()
    {
        Map = locations => from l in locations
                           select new {_ = SpatialIndex.Generate(l.Geo.Lat, l.Geo.Lon)};
    }
}

这似乎有效，我可以像这样对结果进行排序：

RavenQueryStatistics stats;
var query = session.Advanced.LuceneQuery<Location>(Names.Indexes.LocationsByCoordinates)
                       .Statistics(out stats)
                       .WithinRadiusOf(radius, coordinates.Lat, coordinates.Lon);

switch (sort)
{
    case Sort.Distance:
        query = query.SortByDistance();
        break;
    case Sort.Rating:
        query = query.AddOrder(l => l.Reviews.Average(r => r.Rating), true); // TODO: This throws an exception, perhaps a modified index with an aggregate is required? Maybe Map/Reduce?
        break;
    case Sort.Alphabetical:
        query = query.OrderBy(l => l.Name);
        break;
    case Sort.Number_of_ratings:
        query = query.AddOrder(l => l.Reviews.Count, true);
        break;
    case Sort.Relevance: // This is the default ordering in RavenDB.
        break;
    default:
        throw new ArgumentOutOfRangeException("sort");
}

除了按平均评分排序之外，每个选项都可以正常工作，这会引发有关未知字段的异常。我觉得这必须是 Map/Reduce 索引而不是 Map 索引。但我不知道怎么写。

我正在从 MongoDB 迁移此代码，但我曾经在客户端通过评级对文档进行排序，我想我现在会在服务器端执行此操作。

4

1 回答 1

2

由于所有评论都在该位置中，并且您想要每个位置的评论的平均评分，因此您无需降低。只需在地图中创建一个新字段。

Map = locations => from l in locations
                   select new {
                       _ = SpatialIndex.Generate(l.Geo.Lat, l.Geo.Lon),
                       AvgRating = l.Reviews.Average(r => r.Rating)
                   };
于 2012-12-05T17:16:16.950 回答