ADO Overview
Access 2000 supports ADO version 2.1, which includes three ADO data access models: the ADODB library, the ADOX library, and the JRO library. By segmenting data access into three libraries, Access offers a smaller footprint for applications that do not require all three. Another major component of the Access 2000 data access strategy is reliance on OLE DB providers, which work with ADO to offer access to traditional data sources as well as new ones, such as e-mail directories. This vastly expands the power of database programming.
The ADODB library is a small, lightweight library that contains core objects and offers the basics for making connections, issuing commands, and retrieving recordsets, and it also enables recordset navigation. You can use it to perform basic maintenance tasks, such as modifying, adding, and deleting records. The nonhierarchical design of this library makes it easy for beginners.
The ADOX library supports data definition language and security issues. It offers objects that put you in touch with a database's overall schema. For example, it lets you create tables and relations. The model includes support for referential integrity and cascading updates and deletes, and it offers procedures and views as well as Users and Groups collections for user-level database security.
The JRO library enables Jet database replication. Access 2000 supports database replication with both Jet and SQL Server databases. Chapter 11 covers database replication in depth.
One major advantage that ADO offers is an event model. ODBCDirect permits asynchronous operations, but ADO provides events. This frees an application from polling an object and checking its StillExecuting property. Instead, you can simply create event handlers to respond to events whenever they happen. (Subsequent chapters will explain how to design event handlers.)
OLE DB providers help make ADO powerful. They offer a new way to access remote data that embraces and extends ODBC, and they provide access to both relational databases and nontraditional data sources with a consistent ADO interface. Access 2000 ships with a variety of OLE DB providers, including ones for Jet, SQL Server, Oracle, general ODBC data sources, and such nontraditional sources as Microsoft Active Directory Service and Microsoft Index Server. You can expect more of these providers over time.
Before you can use any of the ADO libraries, you must create a reference to at least one of them. You do this from the Visual Basic Editor (VBE) window using the Tools-References command. Figure 2-3 below shows the References dialog box with all three libraries selected. While it might be more convenient to select all three, you can conserve resources by selecting just the libraries that you need. Experiment with the selections for your applications and the machines that they run on to determine what makes sense for your environment. If you have a production application that runs on many different types of machines, you should conserve resources for other application requirements.
Figure 2-3. You use the References dialog box to add ADO libraries to an application.