When to Use the New 3.0 DAO TypeLib in Visual Basic

 Last reviewed: November 27, 1995
Article ID: Q129857
The information in this article applies to:
  • Professional and Enterprise Editions of Microsoft Visual Basic, 16-bit and 32-bit, for Windows, version 4.0

SUMMARY

Visual Basic version 4.0 includes two TypeLibs for data access objects (DAO):

  • Microsoft DAO 2.5/3.0 Compatibility Library TypeLib
  • Microsoft DAO 3.0 Object Library

This article explains when and why you should upgrade to the newer 3.0 TypeLib.

MORE INFORMATION

The Microsoft DAO 2.5/3.0 Compatibility Library is provided for compatibility with older DAO methods. Objects and methods that have changed significantly or were replaced in the newer DAO 3.0 TypeLib are preserved in the DAO 2.5/3.0 TypeLib. These include such things as: DynaSets, SnapShots, and Tables as well as methods (CreateDynaset, CreateSnapshot, and so on) that are specific to these objects.

The DAO 2.5/3.0 also provides access to the new, recommended DAO 3.0 methods (OpenRecordset, and so on). This TypeLib is provided so that your Visual Basic version 3.0 code will port to Visual Basic version 4.0. But once this is completed, Microsoft recommends that you convert to the newer DAO 3.0 methods, which are available only in Visual Basic version 4.0.

The DAO 3.0 TypeLib is provided for speed and forward compatibility. The older DAO methods are not available in the DAO 3.0 TypeLib. It contains only the newer and more efficient methods. If your code runs with the DAO 3.0 TypeLib, it will run with future versions of of the Microsoft Jet database engine. Microsoft recommends that you update your Visual Basic projects so that they run with the DAO 3.0 TypeLib.

How to Change the Version of the DAO TypeLib

You can change the version of the TypeLib that you are using by choosing Tools References from the menu. This brings up a dialog with all of the available TypeLibs.

Note that if you choose to use the newer DAO 3.0 and continue to use obsolete DAO 2.5 methods and objects, you may see some unexpected errors. For example, under DAO 2.5, the following code is perfectly acceptable: 

   Dim DS As Dynaset
   Dim DB As Database
   Set DB = OpenDatabase("Biblio.MDB")
   Set DS = DB.CreateDynaset("Authors")
However, if you chose to use the DAO 3.0 Library, the references to Dynaset and CreateDynaset will generate this error: 

   User-defined type not defined
This is because the Dynaset object and CreateDynaset method do not exist in the DAO 3.0 Library. The code could be rewritten properly as: 

   Dim RS As RecordSet
   Dim DB As Database
   Set DB = DBEngine.Workspaces(0).OpenDatabase("Biblio.Mdb")
   Set RS = DB.OpenRecordSet("Authors", dbOpenDynaset)
Note that when you reload a Project that was saved with a particular TypeLib, Visual Basic detects this and loads the appropriate TypeLib.

Additional reference words: 4.00 vb4win vb4all
KBCategory: kbprg
KBSubcategory: APrgData

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Last reviewed: November 27, 1995
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