Some SQL, some .NET, and whatever else


Refreshing changed .NET SQL CLR assemblies after patching/updates

After applying some Windows updates to one of my servers, I started getting the following error when I ran a customer .NET SQL-CLR stored proc:

Server: Msg 6522, Level 16, State 2, Line 1
A .NET Framework error occurred during execution of user defined routine or aggregate 'somemethodyourecalling':

System.IO.FileLoadException: Could not load file or assembly 'System.Drawing, Version=, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. Assembly in host store has a different signature than assembly in GAC. (Exception from HRESULT: 0x80131050)

I'd imported some additional assemblies into SQL Server for use in SQL CLR mapped stored procedures, and the Windows updates had included a service pack for .NET, which changed some of the assemblies. Now the version I'd linked to SQL Server no longer existed on disk, and SQL couldn't load it - that made sense, and is documented pretty clearly in this MS Support article:

However, I had dozens of servers with SQL CLR components enabled, and hundreds of different assemblies loaded across them all, and not always the same in each server, so a standard update script wouldn't work to refresh all the changed assemblies (the MS Support link provides a list of the standard ones that cause that error, but if you've got custom assemblies loaded, or you've loaded an assembly that's not specifically cleared for SQL CLR, then it's not on the list either). To deal with this, I wrote a script that fetches the assembly list for a database and attempts to refresh every one of them from their disk location. If they haven't changed, the update attempt will fail with a specific error message about the MVID, and there's no change for that assembly.

Also, I've commented out the line that restricts it to just framework assemblies (System.* and Microsoft.*), but you can uncomment that line if you'd like to restrict the refresh from attempting to reload your custom assemblies as well.

DECLARE @AssemblyName VARCHAR(255),
	    @AssemblyLocation VARCHAR(255),
	    @AlterAssemblyCommand NVARCHAR(1024),
	    @DotNetFolder VARCHAR(100)

   SET @DotNetFolder = 'C:\Windows\Microsoft.NET\Framework\v2.0.50727'

		AssemblyName VARCHAR(255),
		AssemblyLocation VARCHAR(255),
		AlterAssemblyCommand NVARCHAR(1024),
		Results VARCHAR(1024)

select as AssemblyName, as Assemblylocation,
		case when charindex('', = 0
			then 'ALTER ASSEMBLY [' + + '] FROM ''' + @DotNetFolder
			else 'ALTER ASSEMBLY [' + + '] FROM '''
		end + + (case right(, 4) when '.dll' then '' else '.dll' end) + ''''
		as AlterAssemblyCommand
INTO #Refresh
from sys.assemblies sa
join sys.assembly_files saf
  on sa.assembly_id = saf.assembly_id
where <> ('Microsoft.SqlServer.Types')
  --and ( like 'System.%' or like 'microsoft.%')

SELECT AssemblyName,
  FROM #Refresh

OPEN Commands

INTO @AssemblyName,


		exec sp_executesql @AlterAssemblyCommand

		insert into #Results
		SELECT @AssemblyName,
				'Assembly refreshed successfully'


		insert into #Results
		SELECT @AssemblyName,
					WHEN 6285 THEN 'No update necessary (MVID match)'
					WHEN 6501 THEN 'Physical assembly not found at specified location (SQL Error 6501)'
					ELSE ERROR_MESSAGE() + ' (SQL Error ' + convert(varchar(10), ERROR_NUMBER()) + ')'


	INTO @AssemblyName,


CLOSE Commands

SELECT * FROM #Results

drop table #refresh
drop table #Results

While troubleshooting the error, I came across this as well - I don't have a SQL 2012 server handy to check with, it looks like this problem might be resolved with a reboot in SQL 2012:

I'm not sure if that's the case, but it would make things easier. Also, it would be nice if there was some kind of "ALTER ASSEMBLY [SomeAssembly] REFRESH" command to address this problem, but maybe in a future version.

Additionally, this error can be caused if the signing of an assembly has changed, but not necessarily the signature, but just reloading it from disk won't work because the method that SQL Server uses to determine if there's been a change is the MVID, and that doesn't change unless there's been a code change of some kind (see the Connect bug here). In those cases, you'll actually need to drop and recreate the assembly, including any supporting objects that rely on that assembly.


Accessing System.DirectoryServices from SQL Server 2005

SQL Server 2005 allows for the integration of .NET assemblies into the databases so that they can be accessed from inside stored procedures and other database functions. Although this is a great new feature, I got hung up on a particularly cryptic error message when I tried to build an assembly and import it.

Since SQL Server makes it difficult to query active directory, and I wanted to build an AD-based authentication module for my database application, the best way to do that seemed to be to use this new feature. My assembly depended on System.DirectoryServices in order to access Active Directory, but that wouldn't be a problem, since the .NET 2.0 framework is available from inside SQL Server 2005 (, provided you've enabled the feature), right? Well, sort of. As it turns out, SQL Server was rushed to RTM too quickly for all of the .NET 2.0 assemblies to be cleared as SAFE, so the ones that weren't fully tested aren't included by default. Fair enough - so it's just a matter of importing System.DirectoryServices, and then importing my assembly that relies on it, right? Again, sort of.

System.DirectoryServices can be imported into SQL Server, but only as an UNSAFE assembly. This has all sorts of other security implications (which is a little ironic, since I was using it to verify user security), but I decided to use it anyway, since I figured that the UNSAFE tag was more of a formality than a real danger, and the assembly would be SAFE once more testing had been done. I imported System.DirectoryServices:

USE master

CREATE ASYMMETRIC KEY asmKey_DirectoryServices
FROM EXECUTABLE FILE = 'c:\Windows\Microsoft.NET\Framework\v2.0.50727\System.DirectoryServices.dll'

CREATE LOGIN asmLogin_DirectoryServices
FROM ASYMMETRIC KEY asmKey_DirectoryServices

GRANT unsafe ASSEMBLY TO asmLogin_DirectoryServices

That imports the System.DirectoryServices assembly as UNSAFE. Next, I imported my assembly as SAFE, since it was signed. The only problem was that when I called my assembly, which reached into System.DirectoryServices, I got an error (I'm calling clrIsMemberOfGroup in my assembly, SqlHelper):

After 4 hours in the phone troubleshooting the issue with Microsoft, it turned out that it was VERY simple, and evenĀ vaguely alluded to in a knowledgebase document. In order to reach into the UNSAFE System.DirectoryServices assembly, I had to make my assembly UNSAFE as well. Since the UNSAFE assembly was running outside the bounds of what .NET considers "SAFE", it could potentially return suspect results, and so anything that relies directly on those results couldn't be considered "SAFE", and had to be tagged as "UNSAFE". It seems like I should be able to implement proper sanitizing code in my assembly so that I don't inherently trust the results from my "UNSAFE" assembly, but SQL Server would have none of it. In order to reach into an UNSAFE assembly, I needed to flag my assembly as UNSAFE - simply placing my assembly import into a "Create key, create login, import assembly" setup like the one I used for System.DirectoryServices fixed the problem.

I suppose the question is really "Did that fix anything?" since all I really did was disable security on those assemblies. It's really hard to throw a security assembly when you don't do any sort of security checks. Well, at least I alleviated the symptoms, and now I'll just wait for SP1 to (hopefully) add System.DirectoryServices (among other missing framework assemblies) to the assemblies accessible from inside the CLR access in SQL Server 2005. I suppose we'll have to wait and see...