我會建立一個基於CTE的視圖和相關的基於表格的函數。我的推理是,雖然你可以在應用程序端實現邏輯,但是這將涉及通過線路發送中間數據以便在應用程序中進行計算。使用DBML設計器,視圖轉換爲表格實體。然後,您可以將該函數與Table實體相關聯,並調用在DataContext上創建的方法來派生視圖定義的類型的對象。使用基於表格的功能允許查詢引擎在構建結果集時考慮您的參數,而不是在事實之後對視圖定義的結果集應用條件。
CREATE TABLE [dbo].[hierarchical_table](
[id] [int] IDENTITY(1,1) NOT NULL,
[parent_id] [int] NULL,
[data] [varchar](255) NOT NULL,
CONSTRAINT [PK_hierarchical_table] PRIMARY KEY CLUSTERED
(
[id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
CREATE VIEW [dbo].[vw_recursive_view]
AS
WITH hierarchy_cte(id, parent_id, data, lvl) AS
(SELECT id, parent_id, data, 0 AS lvl
FROM dbo.hierarchical_table
WHERE (parent_id IS NULL)
UNION ALL
SELECT t1.id, t1.parent_id, t1.data, h.lvl + 1 AS lvl
FROM dbo.hierarchical_table AS t1 INNER JOIN
hierarchy_cte AS h ON t1.parent_id = h.id)
SELECT id, parent_id, data, lvl
FROM hierarchy_cte AS result
CREATE FUNCTION [dbo].[fn_tree_for_parent]
(
@parent int
)
RETURNS
@result TABLE
(
id int not null,
parent_id int,
data varchar(255) not null,
lvl int not null
)
AS
BEGIN
WITH hierarchy_cte(id, parent_id, data, lvl) AS
(SELECT id, parent_id, data, 0 AS lvl
FROM dbo.hierarchical_table
WHERE (id = @parent OR (parent_id IS NULL AND @parent IS NULL))
UNION ALL
SELECT t1.id, t1.parent_id, t1.data, h.lvl + 1 AS lvl
FROM dbo.hierarchical_table AS t1 INNER JOIN
hierarchy_cte AS h ON t1.parent_id = h.id)
INSERT INTO @result
SELECT id, parent_id, data, lvl
FROM hierarchy_cte AS result
RETURN
END
ALTER TABLE [dbo].[hierarchical_table] WITH CHECK ADD CONSTRAINT [FK_hierarchical_table_hierarchical_table] FOREIGN KEY([parent_id])
REFERENCES [dbo].[hierarchical_table] ([id])
ALTER TABLE [dbo].[hierarchical_table] CHECK CONSTRAINT [FK_hierarchical_table_hierarchical_table]
要使用它,你會做這樣的事情 - 假設一些合理的命名方案:
using (DataContext dc = new HierarchicalDataContext())
{
HierarchicalTableEntity h = (from e in dc.HierarchicalTableEntities
select e).First();
var query = dc.FnTreeForParent(h.ID);
foreach (HierarchicalTableViewEntity entity in query) {
...process the tree node...
}
}
我試過了這樣的功能,它似乎是要走的路。它可以從LINQ調用,附加到datacontext。另外,爲什麼既是視圖又是功能? - 它們似乎是重複的 – Anthony 2008-10-15 15:44:10
函數不會映射與表相同的模式。它包括關卡。如果您沒有添加列,可以將其直接映射到表格上。我認爲層次結構中的層次很重要。 – tvanfosson 2008-10-15 16:13:53