Question

我正在尝试转换回存储在CONTEXT_INFO中的nvarchar。

declare @LanguageCode nvarchar(6) = 'en';
declare @binvar varbinary(128);
set @binvar = cast(@LanguageCode as varbinary);
set context_info @binvar;

select A = len(@LanguageCode);
select B = len(convert(nvarchar(6),@LanguageCode));

select C = convert(nvarchar(6),context_info());
select D = cast(CONTEXT_INFO() as nvarchar(5));
select E = len(convert(nvarchar(6),CONTEXT_INFO()));
select F =len(cast(CONTEXT_INFO() as nvarchar(6)));

select G = convert(nvarchar,context_info());
select H = cast(CONTEXT_INFO() as nvarchar);
select I = len(convert(nvarchar,CONTEXT_INFO()));
select J = len(cast(CONTEXT_INFO() as nvarchar));

从将varbinary转换为nvarchar获得的nvarchar的长度为6，它包含\ 0。例如，语言'en'以'en \ 0 \ 0 \ 0 \ 0'的形式获得。这破坏了NHibernate上的密钥缓存。

有没有办法可以将varbinary中存储的nvarchar值转换回原始值？即'en'可以转换回'en'。

输出：

A
-----------
2

B
-----------
2

C
------
en    

D
-----
en   

E
-----------
6

F
-----------
6

G
------------------------------
en                            

H
------------------------------
en                            

I
-----------
30

J
-----------
30

CHOSEN ANSWER理由

我选择了HABO的答案，因为他的解决方案可直接嵌入到消费查询中：

declare @LanguageCode nvarchar(6) = 'en';
declare @binvar varbinary(128);
set @binvar = cast(datalength(@LanguageCode) as varbinary) + cast(@LanguageCode as varbinary);
set context_info @binvar;
select dump = @binvar;



-- directly embeddable
select  recoveredLanguage = convert(nvarchar, substring(context_info(), 5, convert(int, substring(context_info(), 1, 4)) )  ) 
        , theLength =  len ( convert(nvarchar, substring(context_info(), 5, convert(int, substring(context_info(), 1, 4)) )  ) )


declare @buffer varbinary(128) = context_info();
declare @RecoveredLanguageCode nvarchar(6) = cast(substring(@buffer, 5, cast(substring(@buffer, 1, 4) as int)) as nvarchar(6));
select recoveredLanguage = @RecoveredLanguageCode, theLength = len(@RecoveredLanguageCode);

输出：

dump
--------------------
0x0000000465006E00

(1 row(s) affected)

recoveredLanguage              theLength
------------------------------ -----------
en                             2

(1 row(s) affected)

recoveredLanguage theLength
----------------- -----------
en                2

(1 row(s) affected)

虽然souplex的答案是正确的，但我不确定SET ANSI_PADDING_OFF是全局影响还是仅局部影响一批语句。将所有铸件放在一个陈述中会产生副作用，恢复不起作用，每个铸件必须在单独的陈述中完成。无论如何，我赞成了汤米克斯的答案

DECLARE @LanguageCode NVARCHAR(6) = 'en';
DECLARE @binvar VARBINARY(128);
SET @binvar = CAST(@LanguageCode AS VARBINARY(128));
SET context_info @binvar;
select dump = @Binvar;




SET ANSI_PADDING OFF;
select recoveredLanguage = cast( cast( cast(context_info() as binary(128)) as varbinary(128) ) as nvarchar(6) )
        , theLength = len( cast( cast( cast(context_info() as binary(128)) as varbinary(128) ) as nvarchar(6) ) );


DECLARE @binvar1 BINARY(128) = context_info();
DECLARE @binvar2 VARBINARY(128) = CAST(@binvar1 AS VARBINARY(128));
declare @c nvarchar(6) = cast(@binvar2 as nvarchar(6))
select recoveredLanguage = @c, theLength = len(@c);

输出：

dump
----------
0x65006E00

(1 row(s) affected)

recoveredLanguage theLength
----------------- -----------
en                6

(1 row(s) affected)

recoveredLanguage theLength
----------------- -----------
en                2

(1 row(s) affected)

感谢HABO和souplex没有提出XML PATH或XML AUTO解决方案:-)谢谢！

Answer 1

在将字符串保存到CONTEXT_INFO：

之前，将字符串加上长度

declare @LanguageCode nvarchar(6) = 'en';
declare @binvar varbinary(128);
set @binvar = cast(datalength(@LanguageCode) as varbinary) + cast(@LanguageCode as varbinary);
set context_info @binvar;

declare @buffer varbinary(128) = context_info();
declare @RecoveredLanguageCode nvarchar(6) = cast(substring(@buffer, 5, cast(substring(@buffer, 1, 4) as int)) as nvarchar(6));
select @RecoveredLanguageCode, len(@RecoveredLanguageCode);

Answer 2

常规varbinary（128）将是完全可投射的。

DECLARE @LanguageCode NVARCHAR(6) = 'en';
DECLARE @binvar VARBINARY(128);
SET @binvar = CAST(@LanguageCode AS VARBINARY);
SELECT  CAST(@binvar AS NVARCHAR(6));

这会返回初始值'en'。

现在，当您设置上下文值并将其检索回来时，它似乎已变为二进制（128）值而不是varbinary（128）。

SET context_info @binvar;
SELECT  CAST(context_info() AS NVARCHAR(6));

现在你有char（0）个字符。

当您将context_info（）值转换为varbinary并将其强制转换为nvarchar时，当您明确将ansi padding设置为off时，问题就解决了。

SET ANSI_PADDING OFF;
--
DECLARE @LanguageCode NVARCHAR(6) = 'en';
DECLARE @binvar VARBINARY(128);
SET @binvar = CAST(@LanguageCode AS VARBINARY(128));
SET context_info @binvar;

SET ANSI_PADDING ON;
DECLARE @binvar1 BINARY(128) = context_info();
DECLARE @binvar2 VARBINARY(128) = CAST(@binvar1 AS VARBINARY(128));
--> having trailing char(0)
SELECT  CAST(@binvar2 AS NVARCHAR(6));

GO

DECLARE @LanguageCode NVARCHAR(6) = 'en';
DECLARE @binvar VARBINARY(128);
SET @binvar = CAST(@LanguageCode AS VARBINARY(128));
SET context_info @binvar;

SET ANSI_PADDING OFF;
DECLARE @binvar1 BINARY(128) = context_info();
DECLARE @binvar2 VARBINARY(128) = CAST(@binvar1 AS VARBINARY(128));
--> no more trailing char(0)
SELECT  CAST(@binvar2 AS NVARCHAR(6));

SQL Server转换保真度从nvarchar到varbinary，然后从varbinary到nvarchar

2 个答案: