如何解決EF生成嵌套得太深的SQL語句

Question

我在實體框架6中使用了自引用模型，從中我需要根據用戶的選擇來選擇實例。 對於較大的選擇，我得到一個異常：「您的SQL語句的某些部分嵌套過深，重寫查詢或將其分解爲更小的查詢。」

這是我的模型的簡化版本：

public class Hierarchy 
{ 
    public int Id { get; set; } 
    public string Name { get; set; } 
    public int? ParentId { get; set; } 
    public virtual Hierarchy Parent { get; set; } 
    public virtual ICollection<Hierarchy> Children { get; set; } 
} 

由用戶選擇包含了許多的id的。

我的數據庫與

Id Name  ParentId 
1 Root  NULL 
2 parent-1 1 
3 item-1-1 2 
4 item-1-2 2 
5 parent-2 1 
6 item-2-1 2 
7 item-2-2 2 
8 child-1-1-1 3 
9 child-1-1-2 3 
10 child-1-2-1 4 
11 child-1-2-2 4 
12 child-2-1-1 3 
13 child-2-1-2 3 
14 child-2-2-1 4 
15 child-2-2-2 4 

種子我需要檢索所選擇的實例本身，還有，家長和選擇的情況下的兒童。問題在於選擇父母。這是一個Linq查詢，它可以這樣做：

public static List<Hierarchy> Select(List<int> selection) 
{ 
     var result = context.Hierarchy 
      .Where(sub => sub.Children.Select(csub => csub.Id).Intersect(selection).Any()); 
} 

不幸的是，它被轉換爲醜陋的SQL語句。當調用

var test = Hierarchy.Select(new List<int>() { 2, 6, 11 }); 

此被轉換到：

SELECT 
    [Extent1].[Id] AS [Id], 
    [Extent1].[Name] AS [Name], 
    [Extent1].[ParentId] AS [ParentId] 
    FROM [dbo].[Hierarchy] AS [Extent1] 
    WHERE EXISTS (SELECT 
     1 AS [C1] 
     FROM (SELECT 
      [Extent2].[Id] AS [Id] 
      FROM [dbo].[Hierarchy] AS [Extent2] 
      WHERE [Extent1].[Id] = [Extent2].[ParentId] 
     INTERSECT 
      SELECT 
      [UnionAll2].[C1] AS [C1] 
      FROM (SELECT 
       [UnionAll1].[C1] AS [C1] 
       FROM (SELECT 
        2 AS [C1] 
        FROM (SELECT 1 AS X) AS [SingleRowTable1] 
       UNION ALL 
        SELECT 
        6 AS [C1] 
        FROM (SELECT 1 AS X) AS [SingleRowTable2]) AS [UnionAll1] 
      UNION ALL 
       SELECT 
       11 AS [C1] 
       FROM (SELECT 1 AS X) AS [SingleRowTable3]) AS [UnionAll2]) AS [Intersect1] 
    ) 

UnionAll<n>的子查詢A級爲在選擇每個ID添加。實際上，用戶可以選擇多個ID。當有超過40個id的時候，我碰到了一個漏洞抽象並且得到了異常。無論如何，它看起來像是一個次優查詢。

本質上，我的查詢需要找到所有具有任何選定項目的實例作爲子項目。這包括爲每個實例確定兩個列表的交集：選定ID的本地列表和數據庫中每個實例的子列表。

任何人都可以想出一種方法來做到這一點與Linq實體，而不發出查詢每個選擇項目？

Answer 1

可能

public static List<Hierarchy> Select(List<int> selection) 
{ 
    var result = context.Hierarchy 
     .Where(sub => sub.Children.Any(csub => selection.Contains(csub.Id))); 
}