This article discusses what is necessary to take advantage of ActiveX Data Objects (ADO) with Visual Basic.
What is ADO?ActiveX Data Objects is a programming model, which means that it is not dependent upon any given back-end engine. Currently, however, the only engine supporting the ADO model is OLE-DB. There are many native OLE-DB Providers as well as an OLE-DB Provider for ODBC.
The ADO object model consists of six objects:
- Connection: Represents an open connection, in this case to an OLE-DB datasource that can be an ODBC data source, using MSDASQL (the Microsoft OLE-DB provider for ODBC).
- Error: Contains details about data access errors, refreshed for each time an error occurs in a single operation involving ADO.
- Command: Defines a specific command you wish to execute against data.
- Parameters: Optional collection off the command object for any parameters you wish to provide to the command.
- Recordset: Represents a set of records from a table, command object, or SQL Syntax. Can be created without any underlying Connection object.
- Field: Represents a single column of data in a recordset.
- Property: A collection of values raised by the provider for ADO.
- Stream: Provides the means to read or write binary information or text.
- Record: Can represent a row in a recordset or a directory or a file.
Installing ADO on your ComputerTo properly install ADO on your computer, you need to install MDAC. This installs both ADO and necessary underlying ADO components. OLE-DB also requires ODBC version 3.0 or later components.
MDAC is available free for download from the Web at the following URL:
Projects menu, choose References, and then select Microsoft ActiveX Data Objects Library.
The documentation for the ADO Error object indicates that the Errors Collection will be populated if any error occurs within ADO or its underlying provider. This is somewhat incorrect. Depending on the source of the error, ADO's errors collection may not be populated. You need to check both the Visual Basic Error object as well as the ADO Errors collection.
ADO vs. DAOIf you include references to both ADO and DAO in the same project, you may have some difficulty. Both use a Recordset object, so the following code is ambiguous:
You may receive the following error message:
Dim r as recordset
runtime error 13: datatype mismatchTo specify which object model you want to use, include a qualifier in front:
Dim s As ADODB.Recordset
Dim t As DAO.Recordset