F＃SqlDataConnection类型提供程序查询优化

Question

我需要一些帮助来优化使用F＃SqlDataConnection类型提供程序的查询。

有一个表Items与其他4个表的关系：

Type     - n : 1
SubItem1 - m : n
SubItem2 - m : n
SubItem3 - 1 : n

这是类型提供程序查询代码：

query { 
  for x in db.Items do
    join t in db.ItemType on (x.Typy = t.Name)
    select (x, t, x.ItemSubItem1, x.ItemSubItem2, x.SubItem3)
}
|> Seq.map toItem

它生成以下SQL语句：

SELECT [t0].[Id], [t0.Name], [t1].[Name], [t2].[ItemId], [t2].[SubItem1Id], (
    SELECT COUNT(*)
    FROM [dbo].[ItemSubItem1] AS [t3]
    WHERE [t3].[ItemId] = [t0].[Id]
    ) AS [value]
FROM [dbo].[Item] AS [t0]
INNER JOIN [dbo].[ItemType] AS [t1] ON [t0].[Typ] = [t1].[Name]
LEFT OUTER JOIN [dbo].[ItemSubItem1] AS [t2] ON [t2].[ItemId] = [t0].[Id]
ORDER BY [t0].[Id], [t1].[Name], [t2].[SubItem1Id]

问题是只有Type和SubItems1加入。因此，当为toItem中的每个条目调用Items时，将生成2个额外的SQL查询以获取SubItem2和SubItem3。这是非常低效的。

感谢您的帮助！