PRB: RDOErrors Collection Always Empty When Using EXE Server

• Microsoft Visual Basic Standard and Enterprise Editions for Windows, version 5.0

SYMPTOMS

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.

CAUSE

You are obtaining the RDOErrors collection from your application's RDOEngine object rather than from the server method,

RESOLUTION

Provide a method or property on the server object from which to retrieve the RDOErrors collection.

STATUS

This behavior is by design.

MORE INFORMATION

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:

1. Create a new project with a MultiUse class module (named MyConnect) with the following code:

         Public Function Connect () As rdoConnection
           Set Connect = rdoEngine(0).OpenConnection("MyDSN",
                         rdDriverComplete, "uid=sa;pwd=;database=pubs")
         End Function
      
         Public Function Errors () As Variant
           Set Errors = rdoErrors
         End Function
   
   

2. Add a module with the following code:

         Sub Main ()
         End Sub
      
   

1. Add a reference to Microsoft Remote Data Object.

2. Set Sub Main to be the Project Startup Form.

3. 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.

4. Change the project type to ActiveX DLL, name to DLLConnect, compile to a DLL, and save.

5. Change the project type to ActiveX EXE, name to EXEConnect, compile to an EXE, and save.

1. Create a new project with a form and three CommandButtons.

2. 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.

3. 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
   
   

4. 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.