如何编写INSTEAD OF INSERT触发器为任何表设置一列？

Question

我正在开发一个遗留应用程序,该应用程序正在扩展以在多租户配置中运行.基本体系结构采用旧应用程序,并StoreID为每个表添加一列.然后,每个租户通过一组过滤商店ID的视图来查看旧表,例如:

create view AcmeBatWings.data as 
select * from dbo.data d where d.StoreId = 99

它有点比较漂亮,但这简化了问题.

现在,我可以像这样创建一个触发器

create trigger tr_Tenant_fluff on AcmeBatWings
instead of insert
as
insert into AcmeBatWings (Name, StoreId)
select i.Name, 99 from inserted i

假设一个包含Name和StoreId列的简单表.

我的问题是我有100多个表,如果我要遵循这个模式,我将不得不为每个表制作一个专门的触发器,列出每个表的所有字段.短期内令人烦恼的不仅是维护噩梦,因为任何表格更改都需要包含触发器修改.

那么,对于任何具有StoreId的表,如何在每个插入或更新时写入一个触发器,将StoreId字段设置为99？

感谢您帮助SQL新手!

Answer 1

因此,您似乎使用多个模式来传达商店信息,同时保持对象名称一致,每个商店有一个模式,是吗？以及某种连接/用户魔术,以便查询正在查看正确的视图.

如果是这样,我提出了两个令人震惊的黑客和一个推荐的解决方案(所以你知道你的选择).

Egregious hack#1,假设商店视图包括除了 StoreId 之外的基表中的所有列,与基表位于相同的序号位置,并且没有其他列:

CREATE TRIGGER tr_Tenant_fluff ON AcmeBatWings.data
INSTEAD OF INSERT 
AS BEGIN 
  DECLARE @StoreId INT

  SELECT @StoreId = StoreId FROM dbo.StoreSchemas 
  WHERE StoreSchema = OBJECT_SCHEMA_NAME(@@PROCID)

  INSERT dbo.data SELECT *, @StoreId FROM inserted
END

如果您曾向基表添加列,则必须更新所有商店视图以包含该列,否则触发器将中断.

Egregious hack#2,假定与(1)相同,只是StoreId包含在商店视图中:

CREATE TRIGGER tr_Tenant_fluff ON AcmeBatWings.data
INSTEAD OF INSERT 
AS BEGIN 
  DECLARE @StoreId INT

  SELECT @StoreId = StoreId FROM dbo.StoreSchemas 
  WHERE StoreSchema = OBJECT_SCHEMA_NAME(@@PROCID)

  SELECT * INTO #inserted FROM inserted
  UPDATE #inserted SET StoreId = @StoreId

  INSERT dbo.data SELECT * FROM #inserted
END

hack#2优于hack#1的好处是您可以使用定义商店视图SELECT *,如果基表发生更改,您只需重新编译所有商店视图sp_refreshview.缺点是您正在将插入的数据从一个中间表复制到另一个中间表,并更新第二个表.这使得你的INSTEAD OF INSERT触发器的开销增加了两倍,这一开始已经相当昂贵了.即

• INSTEAD OF INSERT触发器的基本开销- >填充成本inserted- > x.
• 成本来填充#inserted从inserted- >约x.
• 更新成本#inserted- >关于x
• 恶劣黑客的总开销#2:大约3x

否则,最好的办法是将触发器编写出来.一旦您熟悉系统表,这是一个相当直接的过程,您可以根据需要调整触发器生成.就此而言,您也应该编写商店视图的脚本.

为了帮助您入门:

CREATE TABLE dbo.data (Name VARCHAR(10), StoreId INT)
GO
CREATE SCHEMA StoreA
GO
CREATE SCHEMA StoreB
GO
CREATE SCHEMA StoreC
GO
CREATE VIEW StoreA.data AS SELECT Name FROM dbo.data WHERE StoreId = 1
GO
CREATE VIEW StoreB.data AS SELECT Name FROM dbo.data WHERE StoreId = 2
GO
CREATE VIEW StoreC.data AS SELECT Name FROM dbo.data WHERE StoreId = 3
GO
CREATE TABLE dbo.StoreSchemas (StoreSchema SYSNAME UNIQUE, StoreId INT PRIMARY KEY)
GO
INSERT dbo.StoreSchemas VALUES ('StoreA', 1), ('StoreB', 2), ('StoreC', 3)
GO

DECLARE @crlf NCHAR(2) = NCHAR(13)+NCHAR(10)
SELECT
  N'CREATE TRIGGER tr_Tenent_fluff ON '+schema_name(v.schema_id)+N'.data'+@crlf
+ N'INSTEAD OF INSERT'+@crlf
+ N'AS BEGIN'+@crlf
+ N'  INSERT dbo.data ('
+ STUFF((
    SELECT @crlf+N'  , '+name FROM sys.columns tc 
    WHERE tc.object_id = t.object_id
      AND (tc.name IN (SELECT name FROM sys.columns vc WHERE vc.object_id = v.object_id)
        OR tc.name = N'StoreId')
    ORDER BY tc.column_id
    FOR XML PATH(''), TYPE).value('.','NVARCHAR(MAX)')
    ,5,1,N' ')+@crlf
+ N'  )'+@crlf
+ N'  SELECT'
+ STUFF((
    SELECT @crlf+N'  , '+name
      + CASE WHEN name = N'StoreId' THEN ' = '+(
          SELECT CONVERT(NVARCHAR,StoreId) FROM dbo.StoreSchemas s 
          WHERE s.StoreSchema = SCHEMA_NAME(v.schema_id)
          )
        ELSE '' END
    FROM sys.columns tc 
    WHERE tc.object_id = t.object_id
      AND (tc.name IN (SELECT name FROM sys.columns vc WHERE vc.object_id = v.object_id)
        OR tc.name = N'StoreId')
    ORDER BY tc.column_id
    FOR XML PATH(''), TYPE).value('.','NVARCHAR(MAX)')
    ,5,1,N' ')+@crlf
+ N'  FROM inserted'+@crlf
+ N'END'+@crlf
+ N'GO'+@crlf
FROM sys.tables t 
JOIN sys.views v 
  ON t.name = v.name 
 AND t.schema_id = SCHEMA_ID('dbo') 
 AND v.schema_id <> t.schema_id
WHERE t.name = 'data'
GO