Working with COM Objects from within T-SQL

December 12, 2000


Introduction
General concepts
OLE Automation Stored Procedures
  • sp_OACreate
  • sp_OADestroy
  • sp_OAGetProperty
  • sp_OASetProperty
  • sp_OAMethod
  • sp_OAGetErrorInfo
  • sp_OAStop
  • Example: generate script
    Literature

    Introduction

    In this article I want to tell you about how you can work with COM objects from within Transact SQL. You can use OLE Automation Stored Procedures (extended stored procedures with sp_OA prefix) to create a COM object in T-SQL and use that object's methods and properties.


    General concepts

    The OLE Automation Stored Procedures, in other words, sp_OA procedures (where OA stands for OLE Automation), allow a connection, through T-SQL commands, to create and use Component Object Model (COM) based objects. These procedures are built into SQL Server as an extended stored procedure.

    Each OLE Automation stored procedure returns an integer code that is the HRESULT returned by the underlying OLE Automation operation. If HRESULT is equal to 0, then all is okay, a nonzero HRESULT indicates OLE error (in hexadecimal format).

    You can use the sp_displayoaerrorinfo stored procedure to display OLE Automation error information (error description, not only hexadecimal code), when error occurs. This very useful procedure is not installed by default, so you can create it manually from SQL Server Books Online.

    See this link for more information (here you can find sp_displayoaerrorinfo stored procedure) "OLE Automation Return Codes and Error Information":
    http://msdn.microsoft.com/library/psdk/sql/8_qd_12_25.htm


    OLE Automation Stored Procedures

    SQL Server supports seven OLE Automation Stored Procedures:

  • sp_OACreate
  • sp_OADestroy
  • sp_OAGetProperty
  • sp_OASetProperty
  • sp_OAMethod
  • sp_OAGetErrorInfo
  • sp_OAStop
  • You can find the description of these stored procedures below.


    sp_OACreate

    First of all, you should call sp_OACreate stored procedure to create an instance of the OLE object. You should pass two parameters into sp_OACreate stored procedure: program ID or class ID and variable. The variable will be a reference to the OLE object for the further using by other sp_OA stored procedures.

    This is the example (for SQL Server 7.0):

    DECLARE @object int
    DECLARE @hr int
    
    -- Create an object that points to the SQL Server
    EXEC @hr = sp_OACreate 'SQLDMO.SQLServer', @object OUT
    IF @hr <> 0
    BEGIN
      EXEC sp_displayoaerrorinfo @object, @hr
      RETURN
    END
    

    NOTE: If you use SQL Server 6.5, you must write 'SQLOLE.SQLServer' instead 'SQLDMO.SQLServer'.

    See this link for more information
    "sp_OACreate (T-SQL)": http://msdn.microsoft.com/library/psdk/sql/sp_oa-oz.htm


    sp_OADestroy

    This stored procedure can be used to destroy a created OLE object. If you don't call sp_OADestroy, the created OLE object will be destroyed automatically when the batch completes execution.

    This is the example:

    -- Destroy the previously created SQL Server object
    EXEC @hr = sp_OADestroy @object
    IF @hr <> 0
    BEGIN
      EXEC sp_displayoaerrorinfo @object, @hr
      RETURN
    END
    

    See this link for more information
    "sp_OADestroy (T-SQL)": http://msdn.microsoft.com/library/psdk/sql/sp_oa-oz_1.htm


    sp_OAGetProperty

    You can use sp_OAGetProperty stored procedure to get a property value of an OLE object.

    See this link for more information
    "sp_OAGetProperty (T-SQL)": http://msdn.microsoft.com/library/psdk/sql/sp_oa-oz_3.htm


    sp_OASetProperty

    You can use sp_OASetProperty stored procedure to set a property of an OLE object to a new value.

    See this link for more information
    "sp_OASetProperty (T-SQL)": http://msdn.microsoft.com/library/psdk/sql/sp_oa-oz_5.htm


    sp_OAMethod

    You can use sp_OAMethod stored procedure to call a method of an OLE object.

    This example calls the VerifyConnection method of the previously created SQL Server object:

    -- Verify the connection
    EXEC @hr = sp_OAMethod @object, 'VerifyConnection', @return OUT
    IF @hr <> 0
    BEGIN
      EXEC sp_displayoaerrorinfo @object, @hr
      RETURN
    END
    

    See this link for more information
    "sp_OAMethod (T-SQL)": http://msdn.microsoft.com/library/psdk/sql/sp_oa-oz_4.htm


    sp_OAGetErrorInfo

    This stored procedure can be used to display OLE Automation error information, when error occurs, as sp_displayoaerrorinfo stored procedure.

    However, easier to use sp_displayoaerrorinfo stored procedure instead of sp_OAGetErrorInfo, because sp_displayoaerrorinfo is a wrapped stored procedure for sp_OAGetErrorInfo.

    See this link for more information
    "sp_OAGetErrorInfo (T-SQL)": http://msdn.microsoft.com/library/psdk/sql/sp_oa-oz_2.htm


    sp_OAStop

    This stored procedure can be used to stop the OLE Automation Stored Procedures execution environment.

    The execution environment will automatically restart the next time you call sp_OACreate stored procedure.

    See this link for more information
    "sp_OAStop (T-SQL)": http://msdn.microsoft.com/library/psdk/sql/sp_oa-oz_6.htm


    Example: generate script

    This script will generate script for all tables and all dependent objects for the given database.

    You can pass the server name, user name, user password, database name and file name into sp_GenerateScript stored procedure, as in the example below:

    EXEC sp_GenerateScript @server = 'Server_Name',
                           @uname = 'User_Name',
                           @pwd = 'Password',
                           @dbname = 'Database_Name',
                           @filename = 'c:\File_Name.sql'
    
    You can specify different number of parameters (from zero to five parameters).

  • If you not specify server name, then the current server will be used;
  • If you not specify database name, then the current database will be used;
  • If you use Windows NT Authentication mode, then you should not specify username and password;
  • If you not specify user name, but specify password, then the current user name will be used;
  • If you not specify password, then password will not be used (for example: username = 'sa' and empty password, you can pass only username in this case);
  • If you not specify file name, then script will be placed into file script.sql on the drive 'c:'.

    This stored procedure can be used for learning some general SQL Server features (how to work with OLE objects from the SQL Server, how to use some system functions, how to work with cursors and so on).

    if object_id('sp_GenerateScript') is not null drop proc sp_GenerateScript
    GO
    
    CREATE PROC sp_GenerateScript (
      @server varchar(30) = null,
      @uname varchar(30) = null,
      @pwd varchar(30) = null,
      @dbname varchar(30) = null,
      @filename varchar(200) = 'c:\script.sql'
    )
    AS
    
    DECLARE @object int
    DECLARE @hr int
    DECLARE @return varchar(200)
    DECLARE @exec_str varchar(200)
    DECLARE @tbname varchar(30)
    
    SET NOCOUNT ON
    
    -- Set the server to the local server
    IF @server is NULL
      SELECT @server = @@servername
    
    -- Set the database to the current database
    IF @dbname is NULL
      SELECT @dbname = db_name()
    
    -- Create an object that points to the SQL Server
    EXEC @hr = sp_OACreate 'SQLDMO.SQLServer', @object OUT
    IF @hr <> 0
    BEGIN
      EXEC sp_displayoaerrorinfo @object, @hr
      RETURN
    END
    
    -- Connect to the SQL Server
    IF (@uname is NULL) AND (@pwd is NULL)
      BEGIN
        -- Windows NT Authentication mode is used
        EXEC @hr = sp_OAMethod @object, 'Connect', NULL,  @server
        IF @hr <> 0
          BEGIN
            EXEC sp_displayoaerrorinfo @object, @hr
            RETURN
          END
      END
    ELSE
    IF (@uname is NULL)
      BEGIN
        -- Set the username to the current user name
        SELECT @uname = SYSTEM_USER
        EXEC @hr = sp_OAMethod @object,'Connect',NULL,@server,@uname,@pwd
        IF @hr <> 0
          BEGIN
            EXEC sp_displayoaerrorinfo @object, @hr
            RETURN
          END
      END
    ELSE
    IF (@pwd is NULL)
      BEGIN
        EXEC @hr = sp_OAMethod @object, 'Connect', NULL,  @server, @uname
        IF @hr <> 0
          BEGIN
            EXEC sp_displayoaerrorinfo @object, @hr
            RETURN
          END
      END
    ELSE
      BEGIN
        EXEC @hr = sp_OAMethod @object,'Connect',NULL,@server,@uname,@pwd
        IF @hr <> 0
          BEGIN
            EXEC sp_displayoaerrorinfo @object, @hr
            RETURN
          END
      END
    
    -- Verify the connection
    EXEC @hr = sp_OAMethod @object, 'VerifyConnection', @return OUT
    IF @hr <> 0
    BEGIN
      EXEC sp_displayoaerrorinfo @object, @hr
      RETURN
    END
    
    SET @exec_str = "DECLARE script_cursor CURSOR FOR SELECT name FROM "
                  + @dbname + "..sysobjects WHERE type = 'U' ORDER BY Name"
    EXEC (@exec_str)
    
    OPEN script_cursor
    FETCH NEXT FROM script_cursor INTO @tbname
    WHILE (@@fetch_status <> -1)
    BEGIN
      SET @exec_str = 'Databases("'+ @dbname +'").Tables("'
                      + RTRIM(UPPER(@tbname))+'").Script(74077,"'
                      + @filename +'")'
      EXEC @hr = sp_OAMethod @object, @exec_str, @return OUT
      IF @hr <> 0
        BEGIN
          EXEC sp_displayoaerrorinfo @object, @hr
          RETURN
        END
      FETCH NEXT FROM script_cursor INTO @tbname
    END
    CLOSE script_cursor
    DEALLOCATE script_cursor
    
    -- Destroy the object
    EXEC @hr = sp_OADestroy @object
    IF @hr <> 0
    BEGIN
      EXEC sp_displayoaerrorinfo @object, @hr
      RETURN
    END
    GO
    


    Literature

    1. SQL Server Books Online

    2. Learning About OLE Automation Stored Procedures
    http://www.sqlmag.com/Articles/Index.cfm?ArticleID=7910

    3. OLE Automation Return Codes and Error Information
    http://msdn.microsoft.com/library/psdk/sql/8_qd_12_25.htm

    4. INF: Protocol Error in TDS Stream Causes Function Sequence Error from OLE Automation SPs
    http://support.microsoft.com/support/kb/articles/Q243/8/99.ASP

    5. OLE Automation Sample Script
    http://msdn.microsoft.com/library/psdk/sql/8_qd_12_28.htm

    6. BUG: Sp_OA Procedures May Produce "Bad Variable Type" or "Type Mismatch" Error
    http://support.microsoft.com/support/kb/articles/Q173/8/48.ASP

    7. PRB: How to Use sp_displayoaerrorinfo in the sp_OA Samples
    http://support.microsoft.com/support/kb/articles/Q151/6/02.asp

    8. INF: Examples of Sp_OA Procedure Use and SQLOLE.Transfer Object
    http://support.microsoft.com/support/kb/articles/Q152/8/01.asp

    9. INF: How Sp_OA Procedures Extension to SQL Server Is Implemented
    http://support.microsoft.com/support/kb/articles/Q180/7/80.ASP

    10.INF: Enabling DLL-Based COM Object Execution Outside SQL Server
    http://support.microsoft.com/support/kb/articles/Q198/8/91.ASP


    » See All Articles by Columnist Alexander Chigrik









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