多映射/减少结果中的 IList<T>？

Question

我正在为 RavenDB 的多映射/归约概念苦苦挣扎，最近向 this question 询问如何正确编写多映射/归约索引。

我得到了那个问题中的简单索引，但是当我试图让它更复杂一点时，我无法让它工作。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，当映射 ChildDocuments 和 RootDocument 的 Items 属性的值时，我尝试将 Items 属性设置为 default(IList)。然而，这不起作用。它给出了错误信息

请求错误无法理解查询：

-- line 2 col 285: 无效的 Expr

-- line 2 col 324: Can't parse double .0.0

上传索引时。如何处理多 map/reduce 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，您的索引中不能有任何复杂的 .net 类型。

在您的示例中，我建议您使用简单的string 而不是IList<string>。然后你可以加入你的字符串项目：

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
    });