多表替代插入触发器

Question

多表替代插入触发器

5

为了一个日志系统，我想要以下的数据库架构：

CREATE TABLE [dbo].[Categories] (
    [Id]       INT            IDENTITY (1, 1) NOT NULL,
    [App]      NVARCHAR (30)  NULL,
    [Source]   NVARCHAR (30)  NULL,
    [LogLevel] NVARCHAR (5)   NULL,
    [Logger]   NVARCHAR (120) NULL,
    CONSTRAINT [PK_Categories] PRIMARY KEY NONCLUSTERED ([Id] ASC),
    CONSTRAINT [UK_Categories] UNIQUE NONCLUSTERED ([App] ASC, [Source] ASC, [LogLevel] ASC, [Logger] ASC)
);

CREATE TABLE [dbo].[Occurences] (
    [PointInTime] BIGINT NOT NULL,
    [CategoryId]  INT    NOT NULL,
    [Noise]       INT    NOT NULL,
    CONSTRAINT [PK_Occurences] PRIMARY KEY CLUSTERED ([PointInTime] ASC, [CategoryId] ASC, [Noise] ASC),
    CONSTRAINT [FK_Category] FOREIGN KEY ([CategoryId]) REFERENCES [Categories] ([Id])
);

设计目标是为了允许大量的日志数据，因为更昂贵的字符串被分解到一个单独的表中。从语义上讲，这两个表形成一个由此视图定义的单一逻辑表：

CREATE VIEW [dbo].[HistoricLogEntries]
    AS SELECT o.PointInTime, o.Noise, c.App, c.[Source], c.LogLevel, c.Logger
    FROM Occurences o
    JOIN Categories c ON o.CategoryId = c.Id;

我现在想在视图上定义一个替代插入触发器，这是我的问题所在。我尝试了以下内容：

CREATE TRIGGER InsteadTrigger on [dbo].[HistoricLogEntries]
INSTEAD OF INSERT
AS
BEGIN
    INSERT INTO Categories
    SELECT i.App, i.[Source], i.LogLevel, i.Logger
    FROM INSERTED i;

    INSERT INTO Occurences
    SELECT i.PointInTime, i.Noise, c.Id AS CategoryId
    FROM INSERTED i
    JOIN Categories c ON i.App = c.App AND i.[Source] = c.[Source] AND i.LogLevel = c.LogLevel AND i.Logger = c.Logger;
END

首先，第一个问题很明显，即第一个插入操作没有检查元组是否已在数据库中存在。如果是单个值插入，我知道如何处理，但在这里我必须考虑多行插入。

另一件我无法解释的事情是，即使第一个插入成功，触发器也不起作用。我会收到外键违规的提示，好像第一个插入实际上没有插入任何内容。

我认为这应该是一个常见的设置，因此可能有人有类似的示例代码吗？

- John

1个回答

网页内容由stack overflow 提供, 点击上面的

可以查看英文原文，
原文链接

- Bogdan Sahlean · Accepted Answer

对于SQL2008及以上版本，我建议使用MERGE语句来插入新的类别：

MERGE dbo.Categories WITH (HOLDLOCK) AS c
USING INSERTED AS i ON i.App = c.App
AND i.[Source] = c.[Source]
AND i.LogLevel = c.LogLevel
AND i.Logger = c.Logger
WHEN NOT MATCHED BY TARGET THEN
    INSERT (App, [Source], LogLevel, Logger)
    VALUES (i.App, i.[Source], i.LogLevel, i.Logger);

我使用了 HOLDLOCK 表提示来防止竞态条件：

[...] 为了避免并发会话使用相同的关键字插入数据，必须获取不兼容的锁以确保只有一个会话可以读取关键字（在此示例中是 UK_Categories 唯一索引），并且该锁必须保持到事务完成为止。[...]

为了避免出现外键错误：

The INSERT statement conflicted with the FOREIGN KEY constraint "FK_Category". The conflict occurred in database "Test", table "dbo.Categories", column 'Id'.

我会在第二个INSERT中添加每个列的名称，如下所示：

INSERT INTO Occurences (PointInTime, Noise, CategoryId)
SELECT i.PointInTime, i.Noise, c.Id AS CategoryId
FROM INSERTED i
JOIN Categories c ON i.App = c.App

这些FK错误的原因是列的顺序不一致：

1）CREATE TABLE中的列顺序为：

   [PointInTime] BIGINT NOT NULL,
    [CategoryId]  INT    NOT NULL,
    [Noise]       INT    NOT NULL,

但是

2）在第二个插入中，列的顺序不同（请参见CategoryId与Noise）：

INSERT INTO Occurences
-- or INSERT INTO Occurences (PointInTime, CategoryId, Noise)
SELECT i.PointInTime, i.Noise, c.Id AS CategoryId
FROM ...

这是我的解决方案：

ALTER TRIGGER InsteadTrigger on [dbo].[HistoricLogEntries]
INSTEAD OF INSERT
AS
BEGIN       
    MERGE dbo.Categories WITH (HOLDLOCK) AS c
    USING INSERTED AS i ON i.App = c.App
    WHEN NOT MATCHED BY TARGET THEN
        INSERT (App)
        VALUES (i.App);

    INSERT INTO Occurences (PointInTime, Noise, CategoryId)
    SELECT i.PointInTime, i.Noise, c.Id AS CategoryId
    FROM INSERTED i
    JOIN Categories c ON i.App = c.App
END
GO