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Get started with CLR integration

  • Article

Applies to: SQL Server

This article provides an overview of the namespaces and libraries required to compile database objects using the SQL Server integration with the .NET Framework common language runtime (CLR). The article also shows you how to write, compile, and run a small CLR stored procedure written in C# and Visual Basic .NET.

Required namespaces

The components required to develop basic CLR database objects are installed with SQL Server. CLR integration functionality is exposed in an assembly called System.Data.dll, which is part of the .NET Framework. This assembly can be found in the Global Assembly Cache (GAC) and in the .NET Framework directory. Typically, a reference to this assembly is automatically added by both command line tools and Visual Studio, so there's no need to add it manually.

The System.Data.dll assembly contains the following namespaces, which are required for compiling CLR database objects:

  • System.Data
  • System.Data.Sql
  • Microsoft.SqlServer.Server
  • System.Data.SqlTypes

Tip

Loading CLR database objects on Linux is supported, but they must be built with the .NET Framework (SQL Server CLR integration doesn't support .NET Core, or .NET 5 and later versions). Also, CLR assemblies with the EXTERNAL_ACCESS or UNSAFE permission set aren't supported on Linux.

Write a "Hello World" stored procedure

Copy and paste the following C# or Visual Basic .NET code into a text editor, and save it in a file named helloworld.cs or helloworld.vb.

using System;
using System.Data;
using Microsoft.SqlServer.Server;
using System.Data.SqlTypes;

public class HelloWorldProc
{
    [Microsoft.SqlServer.Server.SqlProcedure]
    public static void HelloWorld(out string text)
    {
        SqlContext.Pipe.Send("Hello world!" + Environment.NewLine);
        text = "Hello world!";
    }
}

This program contains a single static method on a public class. This method uses two new classes, SqlContext and SqlPipe, for creating managed database objects to output a short text message. The method also assigns the string "Hello world!" as the value of an out parameter. This method can be declared as a stored procedure in SQL Server, and then run in the same manner as a Transact-SQL stored procedure.

Compile this program as a library, load it into SQL Server, and run it as a stored procedure.

Compile the "Hello World" stored procedure

SQL Server installs the .NET Framework redistribution files by default. These files include csc.exe and vbc.exe, the command-line compilers for C# and Visual Basic .NET programs. In order to compile our sample, you must modify your path variable to point to the directory containing csc.exe or vbc.exe. The following path is the default installation path of the .NET Framework.

C:\Windows\Microsoft.NET\Framework\(version)

Version contains the version number of the installed .NET Framework. For example:

C:\Windows\Microsoft.NET\Framework\v4.8.0

Once you add the .NET Framework directory to your path, you can compile the sample stored procedure into an assembly with the following command. The /target option allows you to compile it into an assembly.

For C# source files:

csc /target:library helloworld.cs

For Visual Basic .NET source files:

vbc /target:library helloworld.vb

These commands launch the C# or Visual Basic .NET compiler using the /target option to specify building a library DLL.

Load and run the "Hello World" stored procedure in SQL Server

Once the sample procedure compiles successfully, you can test it in SQL Server. To do this, open SQL Server Management Studio and create a new query, connecting to a suitable test database (for example, the AdventureWorks2022 sample database).

The ability to execute common language runtime (CLR) code is set to OFF by default in SQL Server. The CLR code can be enabled by using the sp_configure system stored procedure. For more information, see Enable CLR integration.

We need to create the assembly so we can access the stored procedure. For this example, we assume that you created the helloworld.dll assembly in the C:\ directory. Add the following Transact-SQL statement to your query.

CREATE ASSEMBLY helloworld from 'C:\helloworld.dll' WITH PERMISSION_SET = SAFE

Once the assembly is created, we can now access our HelloWorld method by using the CREATE PROCEDURE statement. We call our stored procedure hello:

CREATE PROCEDURE hello
(@i NCHAR (25) OUTPUT)
AS EXTERNAL NAME helloworld.HelloWorldProc.HelloWorld;

Note

In the previous example, if the HelloWorldProc class is inside a namespace (called MyNS), the last line in the create procedure statement would be EXTERNAL NAME helloworld.[MyNS.HelloWorldProc].HelloWorld;.

Once the procedure is created, it can be run just like a normal stored procedure written in Transact-SQL. Execute the following command:

DECLARE @J AS NCHAR (25);
EXECUTE hello @J OUTPUT;
PRINT @J;

Here's the expected output.

Hello world!
Hello world!

Remove the "Hello World" stored procedure sample

When you're finished running the sample stored procedure, you can remove the procedure and the assembly from your test database.

First, remove the procedure using the drop procedure command.

IF EXISTS (SELECT name
           FROM sysobjects
           WHERE name = 'hello')
    DROP PROCEDURE hello;

Once the procedure is dropped, you can remove the assembly containing your sample code.

IF EXISTS (SELECT name
           FROM sys.assemblies
           WHERE name = 'helloworld')
    DROP ASSEMBLY helloworld;

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