Question

我正在努力使用RavenDB的多地图/减少概念，并且最近询问this question如何正确编写多地图/减少索引。

我在那个问题中得到了简单的索引，但是当我试图让它变得更复杂时，我无法使它工作。我想要做的是让索引的结果包含一个字符串列表，即：

class RootDocument {
  public string Id { get; set; }
  public string Foo { get; set; }
  public string Bar { get; set; }
  public IList<string> Items { get; set; }
}

public class ChildDocument {
  public string Id { get; set; }
  public string RootId { get; set; }
  public int Value { get; set; }
}

class RootsByIdIndex: AbstractMultiMapIndexCreationTask<RootsByIdIndex.Result> {
  public class Result {
    public string Id { get; set; }
    public string Foo { get; set; }
    public string Bar { get; set; }
    public IList<string> Items { get; set; }
    public int Value { get; set; }
  }

  public RootsByIdIndex() {
    AddMap<ChildDocument>(
      children => from child in children
        select new {
          Id = child.RootId,
          Foo = (string)null,
          Bar = (string)null,
          Items = default(IList<string>),
          Value = child.Value
      });
      AddMap<RootDocument>(
        roots => from root in roots
          select new {
           Id = root.Id,
           Foo = root.Foo,
           Bar = root.Bar,
           Items = root.Items,
           Value = 0
        });
      Reduce = 
        results => from result in results
          group result by result.Id into g
            select new {
              Id = g.Key,
              Foo = g.Select(x => x.Foo).Where(x => x != null).FirstOrDefault(),
              Bar = g.Select(x => x.Bar).Where(x => x != null).FirstOrDefault(),
              Items = g.Select(x => x.Items).Where(
                x => x != default(IList<string>).FirstOrDefault(),
                Value = g.Sum(x => x.Value)
              };
    }
}

基本上，在映射ChildDocuments和RootDocument的Items属性值时，我尝试将Items属性设置为default（IList）。但是，这不起作用。它给出了错误消息

请求时出错无法理解查询：

- 第2行第285栏：无效的Expr

- 第2行col 324：无法解析double .0.0

上传索引时。如何处理多地图/减少索引中的列表？

Answer 1

不要在索引中使用List，而是使用数组。

AddMap<ChildDocument>(
  children => from child in children
    select new {
      Id = child.RootId,
      Foo = (string)null,
      Bar = (string)null,
      Items = new string[0],
      Value = child.Value
  });
  AddMap<RootDocument>(
    roots => from root in roots
      select new {
       Id = root.Id,
       Foo = root.Foo,
       Bar = root.Bar,
       Items = root.Items,
       Value = 0
    });

Reduce = 
    results => from result in results
      group result by result.Id into g
        select new {
          Id = g.Key,
          Foo = g.Select(x => x.Foo).Where(x => x != null).FirstOrDefault(),
          Bar = g.Select(x => x.Bar).Where(x => x != null).FirstOrDefault(),
          Items = g.SelectMany(x=>x.Items),
          Value = g.Sum(x => x.Value)
          };

Answer 2

David，您需要了解RavenDB使用Lucene.NET存储其索引。这意味着，您的索引中不能包含任何复杂的.net类型。

在您的示例中，我建议您使用简单的string代替IList<string>。然后，您可以加入字符串项：

AddMap<ChildDocument>(
  children => from child in children
    select new {
      Id = child.RootId,
      Foo = (string)null,
      Bar = (string)null,
      Items = (string)null,
      Value = child.Value
  });
  AddMap<RootDocument>(
    roots => from root in roots
      select new {
       Id = root.Id,
       Foo = root.Foo,
       Bar = root.Bar,
       Items = string.Join(";", root.Items),
       Value = 0
    });

IList <t>在多地图/减少结果？</t>

2 个答案: