OK, you're ready to write some VB code. Prior to Access 2000, there was a single code library for working with data via recordsets, bookmarks, and so forth: the Data Access Objects (DAO) library. With Access 2000, however, Microsoft introduced a new code library: ActiveX Data Objects (ADO). Whereas DAO was designed specifically for Access's Jet database engine—and may actually offer some performance advantages with data in MDB files—ADO is intended to work with a wider variety of data sources, including any Object Linking and Embedding (OLE) DB sources.
Does this mean that you can now forget about DAO and just work with ADO? Unfortunately, no. For example, the default recordsets that Access uses for bound forms are DAO objects. If you want to work with them, you must use DAO. In general, when you're working strictly inside MDB files (as opposed to using Access as a frontend to another Database Management System [DBMS], such as SQL Server), you may want to use DAO exclusively to avoid confusion. If you need to use a mix of DAO and ADO code, remember to be explicit about which library you are using. When you declare objects such as recordsets or connections, you must be sure to specify which type you mean, like this:
Dim rst1 As DAO.Recordset Dim rst2 As ADODB.Recordset
Whichever library or libraries you use, make sure your database has references to them. In the VB Editor, click Tools → References and make sure Microsoft DAO Object Library and/or Microsoft ActiveX Data Objects Library are checked—use the latest versions. If you plan to use DAO or ADO only, uncheck the reference to the library you won't use to avoid confusion. Note that new databases created in Access 2003 include references to both libraries, while those created in Access 2002 and 2000 include only an ADO reference.
Learn more about this topic from Fixing Access Annoyances.
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