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Adam Machanic

Adam Machanic, Boston-based independent database consultant, writer, and speaker, shares his experiences with programming, performance tuning, and optimizing SQL Server 2000, 2005, and 2008, in conjunction with related technologies such as .NET.

Using static properties in SQLCLR UDTs

I spoke at the Beantown .NET user group meeting tonight, on the topic of SQLCLR in SQL Server 2005.

One of the questions that came up during the UDT part of the talk was whether static properties are supported.  Unfortunately, I had no answer at the time--it's not something I'd yet thought to try.

The answer, as it turns out, is yes: they are supported.  But they must be defined as readonly, e.g.:
public static readonly int foo;
As it turns out, this means that they can also only be initialized from a static constructor:
static myType()
{
    foo = 1;
}
... which means that value will stick around from the time the type is first used, until the AppDomain is reset (for example, if SQL Server is restarted).

In my opinion, this greatly limits many use cases.  One might, I suppose, have some expensive, yet rarely-modified data to initialize the member with, and get that data on the first pass only. However, if the data does chang, I'm not sure that it would be easy to reset the AppDomain.  Do you really want to restart SQL Server in production environments to update static members?

Another use case I can think of is logging.  Perhaps there are situations in which you'd want to log the first time a type is used.  But that doesn't seem incredibly interesting.

If someone else reading has a more compelling use case, I'd be interested in hearing it!
Published Wednesday, July 12, 2006 10:48 PM by Adam Machanic
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Comments

 

Oleg said:

Hi,

I have function and I must have static member in it.

I do not see another way. Also, i detected interesting effect:

1. I have function in  one db

2. I call it, then I change connectin to another db

3. I call this function  again and I have result! but function exists only in the 1st db :-)

using System;

using System.Data;

using System.Data.SqlClient;

using System.Data.SqlTypes;

using Microsoft.SqlServer.Server;

using System.Text.RegularExpressions;

using nvg_net2;

public partial class UserDefinedFunctions

{

   static readonly SynonymFinder sp;

   static UserDefinedFunctions()

   {

       sp = new SynonymFinder();

   }

   [SqlFunction(DataAccess = DataAccessKind.Read)]

   public static SqlString SynonymFinderor(SqlString strInput)

   {

       using (SqlConnection m_connection = new SqlConnection("context connection=true"))

       {

           if (sp != null && !sp.IsInitialized())

           {

               if (m_connection != null && m_connection.State != ConnectionState.Open) m_connection.Open();

               sp.m_connection = m_connection;

               sp.InitObject();

           }

       }

       Regex rx = new Regex(@"\w+");

       string result = rx.Replace(strInput.ToString(), new MatchEvaluator(Synonym));

       return result;

   }

   private static string Synonym(Match m)

   {

       string x = m.ToString();

       string str = "";

       sp.correct(x, ref str);

       if (str == "") str = x;

       return str;

   }

};

November 24, 2008 7:54 AM
 

Firefight said:

I can't believe they implemented static members in SQLCLR this way. They should have made static variables unique to each session/connection. That's how Oracle implemented their package level variables in PL/SQL and static method in their embedded Java implementation, and it's what you want 99.9% of the time.

Now almost every 3rd party library is going to have to be marked as UNSAFE because of this. You almost never want pragmatic information passing accross connections like this, I don't know what they were thinking.

January 12, 2009 4:41 PM
 

Adam Machanic said:

I don't really see the point of having a static member scoped to the session, and this implementation certainly does not prevent you from being able to accomplish that without the use of UNSAFE.  All you need to do, in essence, is set up a keyed collection and use a GUID or something similar to uniquely identify the session.  Some kind of expiration logic would also be necessary, in case the session doesn't call back as planned...

January 13, 2009 10:03 AM

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About Adam Machanic

Adam Machanic is a Boston-based independent database consultant, writer, and speaker. He has been involved in dozens of SQL Server implementations for both high-availability OLTP and large-scale data warehouse applications, and has optimized data access layer performance for several data-intensive applications. Adam has written for numerous web sites and magazines, including SQLblog, Simple Talk, Search SQL Server, SQL Server Professional, CoDe, and VSJ. He has also contributed to several books on SQL Server, including "Expert SQL Server 2005 Development" (Apress, 2007) and "Inside SQL Server 2005: Query Tuning and Optimization" (Microsoft Press, 2007). Adam regularly speaks at user groups, community events, and conferences on a variety of SQL Server and .NET-related topics. He is a Microsoft Most Valuable Professional (MVP) for SQL Server, a Microsoft Certified IT Professional (MCITP), and a member of the INETA North American Speakers Bureau.

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