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How to debug CLR database objects

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Applies to: SQL Server

SQL Server provides support for debugging Transact-SQL and common language runtime (CLR) objects in the database. The key aspects of debugging in SQL Server are the ease of setup and use, and the integration of the SQL Server debugger with the Microsoft Visual Studio debugger. Furthermore, debugging works across languages. Users can step seamlessly into CLR objects from Transact-SQL, and vice versa.

The Transact-SQL debugger in SQL Server Management Studio can't be used to debug managed database objects, but you can debug the objects by using the debuggers in Visual Studio. Managed database object debugging in Visual Studio supports all common debugging features, such as step into and step over statements within routines executing on the server. Debuggers can set breakpoints, inspect the call stack, inspect variables, and modify variable values while debugging.

Debug permissions and restrictions

Debugging is a highly privileged operation, and therefore only members of the sysadmin fixed server role are allowed to do so in SQL Server.

The following restrictions apply while debugging:

  • Debugging CLR routines is restricted to one debugger instance at a time. This limitation applies because all CLR code execution freezes when a break point is hit, and execution doesn't continue until the debugger advances from the break point. However, you can continue debugging Transact-SQL in other connections. Although Transact-SQL debugging doesn't freeze other executions on the server, it can cause other connections to wait by holding a lock.

  • Existing connections can't be debugged, only new connections, as SQL Server requires information about the client and debugger environment before the connection can be made.

We recommend therefore that Transact-SQL and CLR code is debugged on a test server, and not on a production server.

Overview

Debugging in SQL Server follows a per-connection model. A debugger can detect and debug activities only on the client connection it attaches to. Because the functionality of the debugger isn't limited by the type of connection, both tabular data stream (TDS) and HTTP connections can be debugged. However, SQL Server doesn't allow debugging existing connections. Debugging supports all common debugging features within routines executing on the server. The interaction between a debugger and SQL Server happens through distributed Component Object Model (COM).

For more information and scenarios about debugging managed stored procedures, functions, triggers, user-defined types, and aggregates, see SQL Server CLR Integration Database Debugging in the Visual Studio documentation.

The TCP/IP network protocol must be enabled on the SQL Server instance in order to use Visual Studio for remote development, debugging, and development. For more information about enabling TCP/IP protocol on the server, see Configure Client Protocols.

Debug steps

Use the following steps to debug a CLR database object in Microsoft Visual Studio:

  1. Open Microsoft Visual Studio, and create a new SQL Server project. You can use the SQL LocalDB instance that comes with Visual Studio.

  2. Create a new SQL CLR type (C#):

    1. In Solution Explorer, right-click the project, and select Add, New Item....
    2. From the Add New Item window, select SQL CLR C# Stored Procedure, SQL CLR C# User-Defined Function, SQL CLR C# User-Defined Type, SQL CLR C# Trigger, SQL CLR C# Aggregate, or Class.
    3. Specify a name for the source file of the new type, and then select Add.

  3. Add code for the new type to the text editor. For sample code for an example stored procedure, see the following Example section in this article.

  4. Add a script that tests the type:

    1. In Solution Explorer, right-click on the project node and select Add, Script....
    2. In the Add New Item window, select Script (Not in build), and specify a name, such as Test.sql. Select the Add button.
    3. In Solution Explorer, double-click the Test.sql node to open the default test script source file.
    4. Add the test script (one that invokes the code to be debugged) to the text editor. See the example in the next section for a sample script.

  5. Place one or more breakpoints in the source code. Right-click on a line of code in the text editor on the function or routine that you want to debug. Select Breakpoint, Insert Breakpoint. The breakpoint is added, highlighting the line of code in red.

  6. In the Debug menu, select Start Debugging to compile, deploy, and test the project. The test script in Test.sql is run, and the managed database object is invoked.

  7. When the yellow arrow (designating the instruction pointer) appears at the breakpoint, code execution pauses. You can then debug your managed database object:

    1. Use Step Over from the Debug menu to advance the instruction pointer to the next line of code.
    2. Use the Locals window to observe the state of the objects currently highlighted by the instruction pointer.
    3. Add variables to the Watch window. You can observe the state of watched variables throughout the debugging session, even when the variable isn't at the line of code currently highlighted by the instruction pointer.
    4. Select Continue from the Debug menu to advance the instruction pointer to the next breakpoint or to complete execution of the routine if there are no more breakpoints.

Example code

The following C# example returns the SQL Server version to the caller.

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

public class StoredProcedures
{
    [Microsoft.SqlServer.Server.SqlProcedure]
    public static void GetVersion()
    {
        using (var connection = new SqlConnection("context connection=true"))
        {
            connection.Open();
            var command = new SqlCommand("select @@version", connection);
            SqlContext.Pipe.ExecuteAndSend(command);
        }
    }
}

Example test script

The following test script shows how to invoke the GetVersion stored procedure defined in the previous example.

EXECUTE GetVersion;

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