Entity Framework 扩展递归查询

Question

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

我很好奇它是如何工作的？它是否由 SQL 服务器处理，这意味着查询被转换为 CTE（常见的 table 表达式）？

Answer 1

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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

所以这样的查询：

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], 
    [Extent1].[ColumnInt1] AS [ColumnInt1], 
    [Extent1].[ColumnInt2] AS [ColumnInt2], 
    [Extent1].[Parent_ID] AS [Parent_ID]
    FROM [dbo].[EntitySimple] AS [Extent1]),
    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 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发挥作用。