vb6-ado-late-binding

ADO Late Binding — VB6

ADO is accessed via late binding to avoid version-locking the MDAC stack on client machines. No reference to "Microsoft ActiveX Data Objects x.x Library" is added to the project. Both Microsoft SQL Server and PostgreSQL are supported through the same ADO surface, with small naming differences in parameter handling.

1. Declaration and instantiation

' Declarations — always As Object
Private mobjCnn As Object
Private mrsCustomers As Object

' Instantiation — always CreateObject
Set mobjCnn = CreateObject("ADODB.Connection")
Set objRs = CreateObject("ADODB.Recordset")
Set objCmd = CreateObject("ADODB.Command")

Never:

• Dim cnn As ADODB.Connection
• Dim rs As ADODB.Recordset
• Set rs = New ADODB.Recordset
• Adding a reference to the ADO type library

Rationale: different Windows versions ship different MDAC versions. Early binding to a specific type library version causes "ActiveX component can't create object" or "type mismatch" errors when the client has a different version installed. Late binding works against whatever ADO is present.

2. ADO constants — defined locally

Because the type library is not referenced, ADO constants must be defined as local constants or used as literals. The recommended approach for new code is to declare them at the top of any module that uses ADO, or in a shared modADOConstants.bas.

Option Explicit

' Command types
Private Const adCmdText         As Long = 1
Private Const adCmdTable        As Long = 2
Private Const adCmdStoredProc   As Long = 4

' Parameter directions
Private Const adParamInput      As Long = 1
Private Const adParamOutput     As Long = 2
Private Const adParamInputOutput As Long = 3
Private Const adParamReturnValue As Long = 4

' Cursor types
Private Const adOpenForwardOnly As Long = 0
Private Const adOpenKeyset      As Long = 1
Private Const adOpenDynamic     As Long = 2
Private Const adOpenStatic      As Long = 3

' Lock types
Private Const adLockReadOnly    As Long = 1
Private Const adLockPessimistic As Long = 2
Private Const adLockOptimistic  As Long = 3

' Cursor locations
Private Const adUseServer       As Long = 2
Private Const adUseClient       As Long = 3

' Connection states
Private Const adStateClosed     As Long = 0
Private Const adStateOpen       As Long = 1

' Data types (common subset)
Private Const adInteger         As Long = 3
Private Const adBigInt          As Long = 20
Private Const adVarChar         As Long = 200
Private Const adLongVarChar     As Long = 201
Private Const adVarWChar        As Long = 202
Private Const adLongVarWChar    As Long = 203
Private Const adBoolean         As Long = 11
Private Const adCurrency        As Long = 6
Private Const adDouble          As Long = 5
Private Const adDate            As Long = 7
Private Const adDBTimeStamp     As Long = 135
Private Const adGUID            As Long = 72
Private Const adBinary          As Long = 128