Microsoft KB Archive/173409
Article ID: 173409
Article Last Modified on 11/5/2003
- Microsoft Visual Basic 6.0 Learning Edition
- Microsoft Visual Basic 6.0 Professional Edition
- Microsoft Visual Basic 6.0 Enterprise Edition
This article was previously published under Q173409
When calling an Automation server that passes your client application RDO objects, the RDOErrors collection never contains error information if the server is compiled as an ActiveX Automation EXE. RDOErrors collection will contain error information if the server is compiled as an ActiveX Automation DLL.
You are obtaining the RDOErrors collection from your application's RDOEngine object rather than from the server method,
Provide a method or property on the server object from which to retrieve the RDOErrors collection.
This behavior is by design.
When you compile a server component as a DLL, it has access to the same global objects that the client does. Because of this, you can inadvertently engage in practices that break object design principles. When you compile the server to an ActiveX Automation EXE, it now has its own global objects that are separate from the client application and object encapsulation cannot be violated.
Steps to Reproduce Behavior
Create the server:
Create a new project with a MultiUse class module (named MyConnect) with the following code.
Note You must change UID <username> and PWD to the correct values before you run this code. Make sure that UID has the appropriate permissions to perform this operation on the database.
Public Function Connect () As rdoConnection Set Connect = rdoEngine(0).OpenConnection("MyDSN", rdDriverComplete, "uid=<username>;pwd=<strong password>;database=pubs") End Function Public Function Errors () As Variant Set Errors = rdoErrors End Function
Add a module with the following code:
Sub Main () End Sub
- Remove the default form.
- Add a reference to Microsoft Remote Data Object.
- Set Sub Main to be the Project Startup Form.
- In the Project Options dialog, in the Compatibility tab, set Version Compatibility to No Compatibility. This will enable steps 7 and 8 to generate distinct server GUIDs for the EXE and DLL servers.
- Change the project type to ActiveX DLL, name to DLLConnect, compile to a DLL, and save.
- Change the project type to ActiveX EXE, name to EXEConnect, compile to an EXE, and save.
Create the client:
- Create a new project with a form and three CommandButtons.
- Add a reference to Microsoft Remote Data Object, DLLConnect, and EXEConnect. You will have to add the last two by using the Browse feature of the References dialog.
Add the following code:
Private Sub Command1_Click() Dim Connector As DLLConnect.MyConnect Dim Conn As rdoConnection, rs As rdoResultset, E As rdoError rdoEngine.rdoErrors.Clear Set Connector = New DLLConnect.MyConnect Set Conn = Connector.Connect On Error Resume Next Set rs = Conn.OpenResultset("THIS IS BAD SQL") For Each E In rdoErrors MsgBox E.Description Next E Conn.Close End Sub Private Sub Command2_Click() Dim Connector As EXEConnect.MyConnect Dim Conn As rdoConnection Dim rs As rdoResultset Dim E As rdoError rdoEngine.rdoErrors.Clear ' required to prevent previous error ' from showing Set Connector = New EXEConnect.MyConnect Set Conn = Connector.Connect On Error Resume Next Set rs = Conn.OpenResultset("THIS IS BAD SQL") For Each E In rdoErrors MsgBox E.Description Next E Conn.Close End Sub Private Sub Command3_Click() Dim Connector As EXEConnect.MyConnect Dim Conn As rdoConnection Dim rs As rdoResultset Dim E As rdoError Dim Errors As Variant Set Connector = New EXEConnect.MyConnect Set Conn = Connector.Connect Set Errors = Connector.Errors Errors.Clear On Error Resume Next Set rs = Conn.OpenResultset("THIS IS BAD SQL") For Each E In Errors MsgBox E.Description Next E Conn.Close End Sub
- Run the program and press each of the CommandButtons in turn.
Command1 and Command2 both break object programming standards because they refer to the global rdoErrors collection. The code for Command1_Click works (displays errors) because it runs the server as an in-process component, whereas Command2 doesn't work because the server is an out-of-process component and uses a different instance of RDOEngine.
Command3 works with an out-of-process component because it follows object design principles and gets the errors collection from the Connector object and not from the RDOEngine global object.
- This problem can also affect ActiveX components that share DAO objects or other classes that have global objects.
- This problem can also affect Visual Basic 4 and other 32-bit VBA products.
Additional query words: kbRDO Remote OLE kbCOM kbdse kbDSupport kbVBp kbVBp500 kbVBp600
Keywords: kbprb KB173409