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Q170163: INFO: VB 6.0 Readme Part 2: Data Access/Databinding Issues

Article: Q170163
Product(s): Microsoft Visual Basic for Windows
Version(s): 6.0
Operating System(s): 
Keyword(s): kbreadme kbwizard kbtophit kbADO kbAppSetup kbDAOsearch kbDatabase kbDataBinding kbMDAC
Last Modified: 11-JAN-2001

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The information in this article applies to:

- Microsoft Visual Basic Learning Edition for Windows, version 6.0 
- 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 information below includes the documentation and workarounds for Visual
Basic 6.0. This information can also be found in the README.htm file that ships
with Visual Basic 6.0 on the Visual Basic 6.0 CD-ROM. Please see the REFERENCES
section of this article for a list of the Microsoft Knowledge Base articles
relating to the Visual Basic 6.0 readme.

Following is a list of all parts of the readme file:

Part 1. Important Issues - Please Read First!
Part 2. Data Access Issues and DataBinding Tips
Part 3. Control Issues
Part 4. Language Issues
Part 5. Samples Issues
Part 6. Wizard Issues
Part 7. Error Message Issues
Part 8. WebClass Designer Issues
Part 9. DHTML Page Designer Issues
Part 10. Extensibility issues
Part 11. Miscellaneous Issues
Part 12. Microsoft Transaction Server (MTS) Issues
Part 13. Dictionary Object
Part 14. Visual Component Manager
Part 15. Application Performance Manager

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

Error in Data Environment Designer Code Example
-----------------------------------------------

In the topic, "Programmatically Accessing Objects in Your Data Environment
Designer," the example under "Executing a Command Object with Multiple
Parameters" erroneously uses the Open method:

     MyDE.Commands("InsertCustomer").Parameters("ID").value = "34"
     MyDE.Commands("InsertCustomer").Parameters("Name").value = "Fred"
     MyDE.Commands("InsertCustomer").Open

There is no Open method for the Commands object. You must use the Execute method
instead.

Incompatibilities with Data-bound Controls
------------------------------------------

Due to changes in Visual Basic 6.0, not all data-bound controls are compatible
with all data sources. This incompatibility is due to a difference in the
internal binding mechanisms of ADO versus DAO/RDO. Controls that were created
specifically to work with DAO/RDO can't be bound to an ADO Data control;
controls created for use with ADO can't be bound to the standard Data control or
the Remote Data Control.

This incompatibility primarily applies to complex-bound controls such as grids or
lists that bind to multiple fields in a data source; simple-bound controls such
as text boxes or labels that bind to a single field will work with either type
of data source. Some examples are as follows:

- The Microsoft Data Bound Grid control (Dbgrid32.ocx) can be bound to the DAO
  or RDO Data controls; it can't be bound to the ADO Data control.

- The Microsoft DataGrid control (Msdatgrd.ocx) can be bound to the ADO Data
  control; it can't be bound to the DAO or RDO Data controls.

- The Microsoft Masked Edit Control (Msmask32.ocx) can be bound to any of the
  Data controls.

- The intrinsic controls (TextBox, PictureBox, Label, and so on) can be bound
  to any of the Data controls.

- Third-party controls and Visual Basic-authored User controls should be tested
  on a case-by-case basis.

When attempting to bind a control to a data source at design-time, you may
encounter a "No compatible data source" error message. In this case, you will
need to substitute another control that is compatible with your data source.

Binding to Properties of Objects May Yield Unexpected Results
-------------------------------------------------------------

While it is possible to bind any object to any other object, the results may not
always be what you expect. Some properties are read-only bindable and will not
update their bound source.

For example, if you were to bind the Caption property of a Frame control to a
field named Foo in an ADO Recordset object, the Caption would change to reflect
the value of Foo as you scrolled through the Recordset. If, however, you changed
the Caption property programmatically (Frame1.Caption = "Bar"), the value of Foo
would not be updated. Because the Caption property of the Frame is read-only
bindable, it doesn't provide notification that its data has changed.

This isn't a problem for Visual Basic-authored objects, since you can call the
PropertyChanged method in your object's code. For other objects, you can
determine if a property is update bindable by checking the DataBindings
collection. If a property is enumerated in the DataBindings collection, it is
update bindable and the data source will receive updates to data; if it isn't
enumerated, the property is read-only bindable.

Complex Binding to an ADO Recordset Requires CursorType
-------------------------------------------------------

When binding an ADO Recordset object to a complex-bound control (such as a Grid
control), it is necessary to explicitly set the CursorType property to either
adOpenStatic or adOpenKeyset. If you don't set this property, no data will be
displayed. The following code shows the use of the CursorType property:

    Private Sub DataClass_Initialize()
       Set cn = New ADODB.Connection
       Set rs = New ADODB.Recordset
       rs.CursorType = adOpenStatic
       cn.Open "northwind"
       rs.Open "customers", cn
    End Sub

Binding to a simple-bound control (such as a TextBox) doesn't require a specific
CursorType.

Creating Visual Basic Data Sources: Type the Fields as adVarChar

for SQL Server and Access Databases Instead of adBSTR
-----------------------------------------------------

When appending fields to an ADO Recordset object for use with a SQL Server or
Access database, type the fields as adVarChar instead of adBSTR (as shown in
some sample code). When reading data out of either SQL Server or Access
databases, ADO will use the adVarChar type.

Incorrect References for Creating OLE DB Providers
--------------------------------------------------

The documentation erroneously states that it is possible to set a class module's
DataSourceBehavior property to 2 - vbOLEDBProvider to create an OLE DB data
provider. The correct values for DataSourceBehavior are 0 - vbNone and 1 -
vbDataSource.

The documentation also erroneously refers to a non-existent event in class
modules called OnDataConnection.

Finally, in the topic "Creating the MyDataSource Class," the step-by-step example
incorrectly states that you should set DataSourceBehavior to 2 -
vbOLEDBProvider. Instead, you should set DataSourceBehavior to 1 -
vbDataSource.

To create OLE DB data providers using Visual Basic, use the Provider Writer
Toolkit included with the OLE DB SDK. For more information, see the OLE DB
Simple Provider Toolkit in the Platform SDK Documentation on MSDN.

Finding Help For ADO Objects
----------------------------

When using the ADO objects, (for example, Recordset, Connection, Command,
Parameter, ADOR, RDS, and RDS Server object), you cannot get context- sensitive
help on the object or its properties, events, or methods. That is, if you have a
reference to the object and you use one of its features, selecting the code and
pressing F1 does not result in a help topic. Instead, you will get either a
wrong topic or the "Keyword Not Found" topic.

However, you can get help on any of the object's properties, events, or methods
by using the online documentation Index:

1. If the MSDN documentation viewer is not open, on the Help menu, click
  Contents.

2. Click the Index tab.

3. Type the name of the property, event, or method including the word
  "collection", "property", "event", or "method" as appropriate.

4. From the list of available topics, select the topic that includes "ADO" in
  its title.

  NOTE: You can also find additional help on other ADO topics, such as the ADO
  object model, by looking in the MSDN Library Table of Contents: open Platform
  SDK and under Database and Messaging Services, go to Microsoft Data Access
  SDK.

SQL Server OLE DB Provider Requires New instcat.sql
---------------------------------------------------

Before using the SQL Server OLE DB data provider, you must run the version of
instcat.sql distributed with Microsoft Visual Basic 6.0 on SQL Server (version
6.5 and later). Instcat.sql is distributed with Visual Basic 6.0 and can be
found in the \winnt\system32 directory upon installation.

If Instcat.sql is not run on your SQL Server, the provider is unable to retrieve
metadata from the SQL Server, and thus will not be able to connect to that
server.

Setup for Data Access Applications May Fail on Windows 95/98
------------------------------------------------------------

When redistributing a Visual Basic 6.0 application that includes data access
components, setup will fail if DCOM for Windows 95 and Windows 98 isn't present
on Windows 9x client machines.

The file Mdac_typ.exe is added to your setup package by the Package and
Deployment Wizard if your project includes references to ADO, OLEDB, or ODBC
(you can check for this on the Included Files page of the wizard). This file
installs MDAC 2.0 files on the client computer. MDAC 2.0 requires DCOM for
Windows 95 and Windows 98 in order to function properly, however it does not
perform a check for this during setup. The setup will fail if DCOM for Windows
95 and Windows 98 isn't present on the client machine. Some of the older data
access components will be overwritten prior to the failure, possibly causing
older data access applications on the client to fail.

When distributing data access applications for Windows 9x, you need to make sure
that DCOM for Windows 95 and Windows 98 is installed on the client. DCOM98.EXE
is a self-extracting executable file that installs the updated DCOM components
for Windows 95 or Windows 98. It can be found in the DCOM98 directory of the
Visual Basic 6.0 CD. This file may be freely distributed with your Visual Basic
application.

REFERENCES
==========

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

  Q170164 : INFO: VB 6.0 Readme Part 1: Important Issues [ASCII 150] Read
  First!

  Q170162 : INFO: VB 6.0 Readme Part 3: Control Issues

  Q170161 : INFO: VB 6.0 Readme Part 4: Language Issues

  Q170160 : INFO: VB 6.0 Readme Part 5: Samples Issues

  Q190046 : INFO: VB 6.0 Readme Part 6: Wizard Issues

  Q170158 : INFO: VB 6.0 Readme Part 7: Error Message Issues

  Q189539 : INFO: VB 6.0 Readme Part 8: WebClass Designer Issues

  Q190249 : INFO: VB 6.0 Readme Part 9: DHTML Page Designer Issues

  Q170154 : INFO: VB 6.0 Readme Part 10: Extensibility Issues

  Q170157 : INFO: VB 6.0 Readme Part 11: Miscellaneous Issues

  Q170156 : INFO: VB 6.0 Readme Part 12: Transaction Server (MTS) Issues

  Q191792 : INFO: VB 6.0 Readme Part 13: Dictionary Object

  Q191791 : INFO: VB 6.0 Readme Part 14: Visual Component Manager

  Q191790 : INFO: VB 6.0 Readme Part 15: Application Performance Explorer

Additional query words:

======================================================================
Keywords          : kbreadme kbwizard kbtophit kbADO kbAppSetup kbDAOsearch kbDatabase kbDataBinding kbMDAC kbOLEDB kbVBp kbVBp600 kbVS600 kbDataEnv kbMDACNoSweep 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB600Search kbVBA600 kbVB600
Version           : :6.0
Issue type        : kbinfo

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