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。」如何解決EF生成嵌套得太深的SQL語句
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?
這可能要倒退工作,寫,你會看到發出的SQL的情況下,然後揣摩如何創建一個EF投影與之相匹配的。 – Claies 2014-11-25 15:02:21