在欧盟或Concat的类型不能与层次构建 [英] Types in Union or Concat cannot be constructed with hierarchy

问题描述

我试图运行非常类似于以下的查询：

I am trying to run a query very similar to the following:

(from bs in DataContext.TblBookShelf
join b in DataContext.Book on bs.BookID equals b.BookID
where bs.BookShelfID == bookShelfID 
select new BookItem
{
        Categories = String.Join("<br/>", b.BookCategories.Select(x => x.Name).DefaultIfEmpty().ToArray()),
    Name = b.Name,
ISBN = b.ISBN,
BookType = "Shelf"
}).Union(from bs in DataContext.TblBookShelf
join bi in DataContext.TblBookInventory on bs.BookID equals bi.BookID
    select new BookItem
    {
          Categories = String.Join("<br/>", bi.BookCategories.Select(x => x.Name).DefaultIfEmpty().ToArray()),
          Name = bi.Name,
      ISBN = bi.ISBN,
      BookType = "Inventory"
});

我收到了在联盟或Concat的类型不能与层次结构建造的说法执行后，我需要是能够得到的类别，以显示与每本书的列表。如果任何人都可以在一个可能的解决方案提供一些线索，这将大大AP preciated。

I am receiving "Types in Union or Concat cannot be constructed with hierarchy" after the statement executes, I need to to be able to get a list of categories to display with each book. If anyone could shed some light on a possible solution, it would be greatly appreciated.

推荐答案

现在的问题是，你是选择在查询的子序列，你的工会（即 b.BookCategories ）。这是一个LINQ 2 SQL限制。它没有这种转换为SQL（因为这将是很难做到的，所以我想球队选择不支持这一点）。

The problem is that you are selecting a sub-sequence in the queries that you union (i.e. b.BookCategories). This is a LINQ 2 SQL limitation. It fails to translate this to SQL (because it would be very hard to do, so I guess the team chose not to support this).

摆脱子序列选择的。大概在这种情况下，最简单的解决方法是执行联邦客户端。执行两个服务器端的查询和合并的结果。

Get rid of the sub-sequence select. Probably the easiest fix in this case is to execute the union client-side. Execute two server-side queries and merge the results.

性能将是可怕的，因为如果反正序列子选择。您可能希望就如何以有效的方式获取与L2S树研究。

Performance will be horrible anyway because if the sequence sub-select. You might want to research on how to fetch trees with L2S in an efficient way.

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