Question

我在Entity Framework 6中使用自引用模型，我需要根据用户的选择选择实例。对于较大的选择，我得到一个例外：“SQL语句的某些部分嵌套太深。重写查询或将其分解为较小的查询。”

这是我的模型的简化版本：

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; }
}

用户的选择包含许多id。

我的数据库以

播种

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

我需要自己检索所选实例，以及所选实例的父项和子项。问题在于选择父母。这是一个Linq查询，它可以做到：

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，它被转换为丑陋的SQL语句。致电时

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

这会转换为：

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]
    )

为选择中的每个id添加UnionAll<n>子查询级别。在实践中，用户可以选择许多id。如果有超过40个id，我会陷入漏洞抽象并获得异常。在任何情况下，它看起来都是次优查询。

基本上，我的查询需要查找所有具有任何所选项目的实例作为子项。这涉及为每个实例确定两个列表的交集：所选id的本地列表以及数据库中每个实例的子列表。

有人可以想办法使用Linq对实体执行此操作，而不会为每个选择项发出查询吗？

Answer 1

可能是

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

如何解决EF生成嵌套过深的SQL语句

1 个答案: