Question

场景：使用＆＃34;而不是插入＆＃34;触发到另一个表（覆盖插入当前表）会引发截断错误。

尝试将数据插入TableA
而不是触发器设置为在TableA上运行
此触发器反而插入TableB
TableA未写入

问题：

TableA有nvarchar(10) desc列，TableB有nvarchar(200) desc列。在TableA上设置插入触发器，其中desc列的数据长度为50个字符。

如果SET ANSI_WARNINGS ON (为默认值），TableA会导致截断错误。
使用SET ANSI_WARNINGS OFF（危险），在TableB上忽略截断。因此，如果desc以400个字符输入，则会被截断为200个字符且没有错误。

设置

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

CREATE TABLE [dbo].[results]
(
    [id] [int] IDENTITY(1,1) NOT NULL,
    [causefailure] [nvarchar](5) NULL, 
    [type] [nvarchar](50) NOT NULL, 
    [description] [nvarchar](200) NULL,
    [rundate] [datetime] NOT NULL DEFAULT (getdate())
) ON [PRIMARY]
GO

CREATE TABLE [dbo].[test_table]
(
    [id] [int] IDENTITY(1,1) NOT NULL,
    [description] [nvarchar](10) NULL,
    [rundate] [datetime] NOT NULL DEFAULT (getdate())
) ON [PRIMARY]
GO


CREATE TRIGGER [dbo].[InsteadTrigger] 
ON [dbo].[test_table]
INSTEAD OF INSERT
AS
    SET NOCOUNT ON
    SET ANSI_WARNINGS ON
BEGIN
    INSERT INTO results([type], [description])
        SELECT 
            (CASE SUBSTRING([description], 1, 1)
                WHEN 'a' 
                   THEN 'causes failure or truncation'
                   ELSE ''
             END AS [causefailure],
             'Instead Of Trigger' AS [type],
             [description]
        FROM inserted
    END;
GO

ALTER TABLE [dbo].[test_table] ENABLE TRIGGER [InsteadTrigger]
GO

首次尝试：

SET ANSI_WARNINGS OFF

INSERT INTO [dbo].[test_table]([description])
    SELECT 'atest12345678910' AS [description]

第二次尝试：

SET ANSI_WARNINGS ON

INSERT INTO [dbo].[test_table]([description])
    SELECT 'btest12345678910' AS [description]
INSERT INTO [dbo].[test_table]([description])
    SELECT 'atest12345678910' AS [description]

但是当我运行第一个代码段时，causefailure会被截断。但没有错误。运行第二个代码段会在[results]中插入一条记录。但它在第二个引发了例外。

有没有办法忽略：约束，转换问题等，初始写入[test_table]的异常？但是在触发器中完成的任何工作都有例外（例如插入[结果]甚至是[test_tables]的实际工作）？

修改：我不想更改nvarchar(10) desc的列大小在TableA上。最终目标可能是＆＃34;而不是触发＆＃34; 无法在TableA上插入，它保存到TableB。或者它甚至可能会改变 desc的大小在触发器内动态失败并重试插入。

希望有帮助！

Answer 1

以下是如何解决上述问题的不完整的想法。有点回避。但有趣的是测试你可以在多大程度上重做数据库。

以下更改创建或更改表时的架构。在创建或更改表时，在重命名表后，它将被换出为索引视图。

ALTER TRIGGER trigger_CreateTable
    ON DATABASE
    AFTER CREATE_TABLE, ALTER_TABLE
AS
BEGIN
    --SELECT EVENTDATA()

    DECLARE @Prefix AS nvarchar(256) = N'PleaseUseView_'

    DECLARE @Event AS XML = EVENTDATA()
    DECLARE @SchemaName AS nvarchar(255) = (@Event.value('(/EVENT_INSTANCE/SchemaName)[1]',  'NVARCHAR(255)')) 
    DECLARE @TableName AS nvarchar(255) = (@Event.value('(/EVENT_INSTANCE/ObjectName)[1]',  'NVARCHAR(255)')) 
    DECLARE @ObjectType AS nvarchar(255) = (@Event.value('(/EVENT_INSTANCE/ObjectType)[1]',  'NVARCHAR(255)'))
    DECLARE @TableWithSchema AS nvarchar(512) = '[' + @SchemaName + '].[' + @TableName + ']'

    CREATE TABLE #SchemaBindingDependencies
    (
        [id] int NOT NULL IDENTITY,
        [schema] nvarchar(256) NOT NULL,
        [name] nvarchar(256) NOT NULL
    )

    INSERT INTO #SchemaBindingDependencies([schema], [name])
        SELECT DISTINCT s.name AS [schema], o.name
        FROM sys.objects AS o
            INNER JOIN sysdepends AS d
                ON d.id = o.[object_id]
            INNER JOIN sys.schemas AS s
                ON s.[schema_id] = o.[schema_id]
        WHERE     o.type ='V' AND d.depid = OBJECT_ID(@TableWithSchema)
              AND SUBSTRING(@TableName, LEN(@Prefix) + 1, 256) LIKE o.[name]

    IF (EXISTS(SELECT 1 FROM #SchemaBindingDependencies))
    BEGIN
        DECLARE @Index AS int = (SELECT MAX(id) FROM #SchemaBindingDependencies)
        WHILE (@Index > 0)
        BEGIN
            DECLARE @ViewName1 AS nvarchar(256) = (SELECT [name] FROM #SchemaBindingDependencies WHERE id = @Index)
            IF (@ViewName1 IS NOT NULL)
            BEGIN
                DECLARE @SchemaName1 AS nvarchar(256) = (SELECT [schema] FROM #SchemaBindingDependencies WHERE id = @Index)
                DECLARE @DropSchemaBoundViewQuery AS nvarchar(1000) = 'DROP VIEW [' + @SchemaName + '].[' + @ViewName1 + ']'

                EXEC(@DropSchemaBoundViewQuery)
            END

            SET @Index = @Index - 1
        END
    END

    IF (SUBSTRING(@TableName, 1, LEN(@Prefix)) <> @Prefix)
    BEGIN
        DECLARE @NewTableName AS nvarchar(512) = @Prefix + @TableName + ''
        DECLARE @NewTableWithSchema AS nvarchar(512) = '[' + @SchemaName + '].[' + @NewTableName + ']'

        EXEC sp_rename @TableWithSchema, @NewTableName

        SET @TableName = @NewTableName
        SET @TableWithSchema = '[' + @SchemaName + '].[' + @NewTableName + ']'
    END

    DECLARE @Columns AS nvarchar(max) = (STUFF((SELECT ',[' + x.[name] + ']' FROM (
        SELECT c.[name]
        FROM sys.columns AS c
            INNER JOIN sys.tables AS t
                ON t.[object_id] = c.[object_id]
            INNER JOIN sys.schemas AS s
                ON s.[schema_id] = t.[schema_id]
        WHERE t.[name] = @TableName AND s.[name] = @SchemaName) AS x FOR XML PATH('')), 1, 1, ''))

    DECLARE @ViewName AS nvarchar(256) = SUBSTRING(@TableName, LEN(@Prefix) + 1, 256)
    DECLARE @ViewWithSchema AS nvarchar(512) = '[' + @SchemaName + '].[' + @ViewName + ']'

    DECLARE @Query AS nvarchar(max) =
        N'CREATE VIEW ' + @ViewWithSchema + N' ' + CHAR(10) + CHAR(13) +
        N'WITH SCHEMABINDING ' + CHAR(10) + CHAR(13) +
        N'AS ' + CHAR(10) + CHAR(13) +
        N'  SELECT ' + @Columns + ' ' + CHAR(10) + CHAR(13) +
        N'  FROM ' + @TableWithSchema + N' '
    --SELECT @Query
    EXEC(@Query)

    SET @Query =
        N'CREATE UNIQUE CLUSTERED INDEX [CIX_' + @ViewName + N'] ' + CHAR(10) + CHAR(13) +
        N'ON ' + @ViewWithSchema + N'(' + @Columns + N')'
    EXEC(@Query)

    -- TODO: Use the below double commented to build a variable insert statement for the "Instead of TRIGGER"
    --
    ----DECLARE @tv_source TABLE (id int)
    ----declare @XML xml;
    ----set @XML = 
    ----  (
    ----  select top(0) *
    ----  from @tv_source
    ----  for XML RAW, ELEMENTS, XMLSCHEMA  
    ----  );
    ----SELECT T.c.query('.'), T.c.value('@name', 'nvarchar(256)')
    ----FROM @XML.nodes('/*/*/*/*/*') AS T(c)
    --
    --SET @Query =
    --  N'CREATE TRIGGER [Trigger_' + @ViewName + N'] ' + CHAR(10) + CHAR(13) +
    --  N'ON ' + @ViewWithSchema + N' ' + CHAR(10) + CHAR(13) +
    --  N'INSTEAD OF INSERT ' + CHAR(10) + CHAR(13) +
    --  N'AS BEGIN ' + CHAR(10) + CHAR(13) +
    --  N'BEGIN TRY ' + CHAR(10) + CHAR(13) +
    --  N' INSERT INTO ' + @TableWithSchema + N'(' + @Columns + N')'
    --  N'   SELECT ' + @Columns + 
    --EXEC(@Query)
END

理想情况下，您将为表使用不同的架构。并使用dbo或视图的默认值。

Instead of TRIGGER工作后，你可以在它周围包裹一个TRY / CATCH。在catch上，检查schema以进行截断。并根据需要扩展列大小。

不完整的解决方案。但这是我现在坚持的答案。如果有人有更好的答案或完整的解决方案，请添加它！

TL;博士

一个有趣的事情是以下查询

DECLARE @tv_source TABLE (id int)
declare @XML xml;
select top(0) *
from @tv_source
for XML RAW, ELEMENTS, XMLSCHEMA

您可以返回架构。上述XML的SOAP。或者JsonSchema或Avro如果使用SQL 2016+ Json版本来构建具有模式感知的Restful API。通过模式感知，应用程序网关可以将许多分散的Micro-Rest API自动抓取到一个看起来很大的Rest API中。

SQL Server - 而不是插入触发器 - 覆盖截断错误？

1 个答案: