Question

我有一个场景，我想分批存储小文档，因为插入性能。但我当然希望能够搜索各个项目。

public class Batch
{
    public Guid Id { get; set; }
    public Item[] Items { get; set; }
}

public class Item
{
    public int Id { get; set; }
    public string Description { get; set; }
}

假设我想按描述搜索，并且我想要返回ID。我创建了以下非常简单的map / reduce索引，我希望这样做：

Map = batches =>
    from batch in batches
    from item in batch.Items
    select new Result
        {
             Description = item.Description,
             ItemIds = new[] {item.Id}
        };

Reduce = results =>
    from result in results
    group result by result.Description into g
    select new Result
        {
             Description = g.Key,
             ItemIds = g.SelectMany(x => x.ItemIds).ToArray()
        };

使用此索引的查询不会失败，它只会返回任何结果。

如果索引被修改了一点，使用string.Join而不是SelectMany来获取ID，一切正常。

Map = batches =>
     from batch in batches
     from item in batch.Items
     select new Result
         {
             Description = item.Description,
             ItemIdsAsString = item.Id.ToString(),
         };

Reduce = results =>
     from result in results
     group result by result.Description into g
     select new Result
         {
             Description = g.Key,
             ItemIdsAsString = string.Join("|", g.Select(x => x.ItemIdsAsString)),
         };

行为完全相同，只是ID现在存储为“2 | 5 | 7”而不是这些整数的数组。但这一次，索引产生了正确的结果。

A full test can be found here

为什么SelectMany在Reduce表达式中不起作用？

RavenDB Reduce表达式中不支持SelectMany吗？

0 个答案: