DOCUMENT:Q193866 01-MAR-2002 [vbwin]
TITLE :HOWTO: Use the VB 6.0 DataEnvironment with Parameterized Queries
PRODUCT :Microsoft Visual Basic for Windows
PROD/VER::6.0
OPER/SYS:
KEYWORDS:kbGrpDSVBDB
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The information in this article applies to:
- Microsoft Visual Basic Professional Edition for Windows, version 6.0
- Microsoft Visual Basic Enterprise Edition for Windows, version 6.0
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SUMMARY
=======
The Visual Basic 6.0 DataEnvironment simplifies the process of building
parameterized queries. However, using these queries with bound controls may not
behave the way you would expect. This article is designed to explain how these
queries interact with the bound controls and to help ensure that you can utilize
these queries in your application.
NOTE: This article assumes that you are working with a SQL Server database. The
DataEnvironment makes a number of OLE DB API calls at design-time in order to
retrieve data about the parameters in your query. Not all OLE DB providers or
ODBC drivers return information about the name, data type and direction for the
query's parameters. As a result, using parameterized queries with the
DataEnvironment is not supported for all drivers and providers. This
functionality is supported for the SQL Server and Oracle OLE DB providers and
ODBC drivers that are included with Microsoft Visual Basic 6.0.
MORE INFORMATION
================
If you are using a parameterized query in the DataEnvironment with bound
controls, you may notice that the controls appear empty when you run the form,
and that running the query via code does not populate your controls. This
behavior is by design.
When you display a form with a control bound to the DataEnvironment and you have
not yet run that query, the DataEnvironment will automatically run that query.
In the case of a parameterized query, the DataEnvironment may not have all of
the information necessary to run the query. The attempt to run the query fails
and no data is returned. Thus, the control does not contain data.
If you then run the query via code, the DataEnvironment will retrieve the results
of the query. This data will not appear in the bound control until it is
re-bound.
Steps to Reproduce Behavior
---------------------------
1. Create a Standard EXE project in Visual Basic. Form1 is created by default.
2. Add a DataEnvironment to the project. Connection1 is created by default.
3. Set Connection1 to use the SQLOLEDB provider to connect to the your server's
Pubs database.
4. Add a command to Connection1 based on the following query, and name the
command GetAnAuthor:
SELECT * FROM Authors WHERE Au_ID = ?
5. Right-click and drag the command onto Form1 and choose "Data Grid."
6. Add a textbox to Form1 from the toolbox and name it txtParameter.
7. Add a CommandButton to Form1 from the toolbox and name it cmdRunQuery. Set
its Caption property to "Run Query."
8. Add the following code to the cmdRunQuery_Click event:
With DataEnvironment1
If .rsGetAnAuthor.State = adStateOpen Then
.rsGetAnAuthor.Close
End If
.GetAnAuthor txtParameter.Text
If .rsGetAnAuthor.RecordCount > 0 Then
MsgBox "Found " & .rsGetAnAuthor.Fields("Au_LName").Value
Else
MsgBox "No author found"
End If
End With
The If block closes the recordset if it was previously open before running the
parameterized query.
9. Run the project, and place an author ID in the textbox. "172-32-1176" and
"213-46-8915" are the first two author ID values in the original table.
(Viewing the contents of the table via the DataView window may be helpful.)
Once you've entered an existing author ID in the textbox, click the command
button. A dialog box is displayed to tell you whether the query returned an
author. Note that even if the query did return an author, the record does not
appear in the grid.
10. Add the following line to the end of the cmdRunQuery_Click event:
Set DataGrid1.DataSource = DataEnvironment1
11. Run the project again. Place a valid author ID in the textbox and click on
the command button. If your query returned data, you will see that data in
the grid once you close the dialog box.
ADDITIONAL INFORMATION
----------------------
There are other ways to use parameterized queries with the DataEnvironment"
- Supply a value for the parameter at design-time. For example, in the sample
above, you could return to the GetAnAuthor command in the DataEnvironment,
click on the Parameters tab, and supply a value for the parameter in the
textbox marked Value. If you run this project with a value for the parameter
set at design-time, you'll see the results of that query using that parameter
when the form loads because the bound control forced an initial execution of
that query. If you re-run the command with a new value for the parameter, you
will not see the new data in the bound controls until you re-bind them as
shown above.
- Make sure that you explicitly execute the query prior to displaying the
controls bound to that query. For example, you can use one form to ask the
user for the value of the parameter. Then you can execute the query and
display a form that will show the results of the query. Keep in mind that if
you want to show that same form with the results of multiple executions of
the query, you will need to make sure the recordset object is closed prior to
executing the query, and then re-bind the controls (as shown above).
(c) Microsoft Corporation 1998. All Rights Reserved.
Contributions by David Sceppa, Microsoft Corporation
Additional query words: kbDSupport kbdse DataEnvironment Parameterized Bound kbVBp600 kbDataBinding kbDataEnv kbDatabase kbVBp kbVS600
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Keywords : kbGrpDSVBDB
Technology : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB600Search kbVB600
Version : :6.0
Issue type : kbhowto
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