实体框架扩展递归查询

问题描述

流行的 EF 扩展库中提供了分层查询支持：https://entityframework-extensions.net/to-self-hierarchy-list。

我很好奇它到底是如何工作的？是否由 sql 服务器处理，意味着查询被转换为 CTE（公共表表达式）？

解决方法

免责声明：我是 Entity Framework Extensions

的所有者

你没看错，我们确实在生成的 SQL 中使用了 CTE。

SQL 模板的外观如下：

WITH
    SelfHierarchyQueryOuter AS (@(sqlMaster)),SelfHierarchyQueryInner AS (@(sqlHierarchy)),SelfHierarchyQuery AS (SELECT A.*,0 AS ZZZ_Recursion FROM (SELECT * FROM SelfHierarchyQueryOuter) AS A 
                                    UNION ALL
                                    SELECT B.*,ZZZ_Recursion + 1 AS ZZZ_Recursion FROM  (SELECT * FROM SelfHierarchyQueryInner) AS B
                                    INNER JOIN SelfHierarchyQuery AS C ON @(keyJoins) 
                                    WHERE ZZZ_Recursion < @(maxRecursion)
                                    )

@(selectFinal)
FROM    SelfHierarchyQuery

这样的查询：

var list2 = context.EntitySimples.ToSelfHierarchyList(x => x.Parent,options => options.MaxRecursion = 5);

将生成以下 SQL：

WITH
    SelfHierarchyQueryOuter AS (SELECT TOP 100 PERCENT  
    [Extent1].[ID] AS [ID],[Extent1].[ColumnInt1] AS [ColumnInt1],[Extent1].[ColumnInt2] AS [ColumnInt2],[Extent1].[Parent_ID] AS [Parent_ID]
    FROM [dbo].[EntitySimple] AS [Extent1]),SelfHierarchyQueryInner AS (SELECT TOP 100 PERCENT  
    [Extent1].[ID] AS [ID],ZZZ_Recursion + 1 AS ZZZ_Recursion FROM  (SELECT * FROM SelfHierarchyQueryInner) AS B
                                    INNER JOIN SelfHierarchyQuery AS C ON C.[Parent_ID] = B.[ID] 
                                    WHERE ZZZ_Recursion < 5
                                    )

SELECT *
FROM    SelfHierarchyQuery

这里没有什么“特别”之处，只是使用了 CTE 的一项重要功能使其工作。