我会建立一个基于CTE的视图和相关的基于表格的函数。我的推理是,虽然你可以在应用程序端实现逻辑,但是这将涉及通过线路发送中间数据以便在应用程序中进行计算。使用DBML设计器,视图转换为表格实体。然后,您可以将该函数与Table实体相关联,并调用在DataContext上创建的方法来派生视图定义的类型的对象。使用基于表格的功能允许查询引擎在构建结果集时考虑您的参数,而不是在事实之后对视图定义的结果集应用条件。
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,你会做这样的事情 - 假设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...
}
}
我试过了这样的功能,它似乎是要走的路。它可以从LINQ调用,附加到datacontext。另外,为什么既是视图又是功能? - 它们似乎是重复的 – Anthony 2008-10-15 15:44:10
函数不会映射与表相同的模式。它包括关卡。如果您没有添加列,可以将其直接映射到表格上。我认为层次结构中的层次很重要。 – tvanfosson 2008-10-15 16:13:53