Q170368: PRB: "Invalid Cursor Position" Using UserConnection to GetChunk

Article: Q170368
Product(s): Microsoft Visual Basic for Windows
Version(s): 
Operating System(s): 
Keyword(s): kbGrpDSVBDB
Last Modified: 09-JAN-2000

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The information in this article applies to:

- Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0 
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SYMPTOMS
========

When you use the UserConnection Designer to establish a connection and retrieve
an RDO result set, you will encounter the following error:

  "Run-Time error '40002'
  S1109:[Microsoft][ODBC SQL Server Driver] Invalid Cursor Position"

if the RDO result set includes a BLOB (Binary Large Object) column and you do not
change any default values.

This error occurs at the GetChunk method.

CAUSE
=====

Due to the ODBC limitation, GetChunk fails when you use a Forward only cursor
with Rowset Size > 1. Using UserConnection Designer, the default cursor is
Forward only, and Rowset Size is 500. This causes "Invalid Cursor Position"
error.

RESOLUTION
==========

To get BLOB data using a Forward-only cursor, you can:

- Set the Rowset Size to 1 on the Advanced tab of UserConnection Queryset
  object Properties page.

  -and-

- Set Cursor Library to "Use server-side cursors" or "Use None" on the
  Miscellaneous tab of UserConnection object Properties page.

You could also open a Keyset type resultset in code by setting the CursorType
property of your RdoQuery object before executing the query, such as the
following:

     Dim cn As New UserConnection1
     Dim rs as rdoResultset

     cn.EstablishConnection                            'establish connection
     cn.rdoQueries("Query1").CursorType = rdOpenKeyset 'define cursortype
     cn.Query1                                         'execute the query
     Set rs = cn.LastQueryResults

MORE INFORMATION
================

The following example uses pub_info table in Pubs database, because pub_info has
a TEXT column, pr_info.

Steps to Reproduce Behavior
---------------------------

Task One: Create the UserConnection

1. Start a new project in Visual Basic and choose "Standard EXE." Form1 is
  created by default.

2. On the Project menu, click Components, click the Designer tab, and then place
  a check next to Microsoft UserConnection.

3. On the Project menu, click Add ActiveX Designer, and then click Microsoft
  UserConnection. This will bring up a dialog titled UserConnection1
  Properties.

4. On the Connection tab, select either a DSN or DSN-less connection and fill in
  the appropriate information. If you select DSN-less, make sure you specify a
  database in the Other ODBC Attributes area with database=Pubs. On the
  Authentication tab, fill in your username and password, and place a check
  next to Save Connection Information for Design Time.

5. Click OK to save this information, and return to the Designer window.

6. Insert a new Query by right-clicking on UserConnection1 and choosing Insert
  Query or by clicking on the Insert Query toolbar icon.

7. From the Source of Query, choose Based on User-Defined SQL. Then type the
  following SQL into the TextBox:

  Select pub_id, pr_info From pub_info

8. Click OK to save this information.

Task Two: Build the Visual Basic Code

1. Add a CommandButton, Command1, to Form1.

2. Add a TextBox, Text1, to Form1. Set the MultiLine property to True;
  ScrollBars property to 3 - Both.

3. In the Command1_Click() event, paste the following code:

        Private Sub Command1_Click()
           Dim cn As New UserConnection1
           Dim rs As rdoResultset
           Dim ColSize As Long
           With cn
              .EstablishConnection       'Establish connection

      ' **** Un-comment the following line to change default cursor to Keyset
      '       .rdoQueries("Query1").CursorType = rdOpenKeyset
      ' ****
              .Query1
           End With

           Set rs = cn.LastQueryResults
           If rs!pr_Info.ChunkRequired Then
              ColSize = rs!pr_info.ColumnSize
              Text1.Text = rs!pr_info.GetChunk(ColSize)
           Else
              Text1.Text = rs!pr_info
           End If

           rs.Close
           cn.Close
        End Sub

4. Start the program or press the F5 key.

REFERENCES
==========

For additional information, please see the following articles in the Microsoft
Knowledge Base:

  Q166281 : HOWTO: Create and Implement a UserConnection

  Q153238 : HOWTO: Use GetChunk and AppendChunk Methods of RDO Object

(c) Microsoft Corporation 1997, All Rights Reserved.
Contributions by Adrian Chiang, Microsoft Corporation


Additional query words: kbVBp500 kbVBp600 kbVBp kbdse kbDSupport

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Keywords          : kbGrpDSVBDB 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVB500 kbVB600
Issue type        : kbprb

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