INFO: Choosing an rdoResultset Cursortype

ID: Q149054

The information in this article applies to:

Microsoft Visual Basic Professional and Enterprise Editions for Windows, version 5.0
Microsoft Visual Basic Enterprise Edition, 32-bit only, for Windows, version 4.0

SUMMARY

This article describes the types of rdoResultset cursors in RDO and when to use them.

NOTE: The following text comes directly from the Visual Basic online Help. Because there are no hot-links to the online Help, you must search for information explicitly. Go into Help, click on the Search button, click on the Find tab, type in Cursors, and then select Choosing a cursor type.

MORE INFORMATION

Choosing the right cursor for an application impacts performance and resource management. Your choice of cursor depends on how many rows you intend to access, how you need to navigate through the result set, how membership is determined, and how you intend to update the data.

In many cases, use of the forward-only type result set is the best choice as it exposes only one row of the result set at a time and is far easier for RDO to create. However, it is not a cursor and does not permit access to more than one row at a time.

Server-Side Cursor Support

An important aspect of keyset or dynamic cursors is where the keyset is created. If the server supports server-side cursors, as with Microsoft SQL Server 6.0 and above, you can specify that the cursor keyset is created and maintained on the server.

Selecting a Cursor Type

To select a specific type of rdoResultset cursor, set the RemoteData control's ResultsetType property or the type argument of the OpenResultset method to:


   Resultset type  Constant
   -------------------------------------------
   Forward-only    (Default) rdOpenForwardOnly
   Static          rdOpenStatic
   Keyset          rdOpenKeyset
   Dynamic         rdOpenDynamic

Available Cursor Types

The following table summarizes the four types of rdoResultset cursors:
```
   Attribute          Forward-only  Static     Keyset    Dynamic
   -------------------------------------------------------------
   Updatable          Yes (SS)      No (SS)    Yes       Yes
                      No (CL)       Yes (CL)
   Membership         Fixed         Fixed      Fixed     Dynamic
   Visibility         One row       Cursor     Cursor    Cursor
   Move current row   Forward       Anywhere   Anywhere  Anywhere
   Result of a join   Yes           Yes        Yes       Yes
 
```
NOTE: CL indicates that support for this cursor is provided by the ODBC cursor library. SS indicates support by Microsoft SQL Server.

Choose the type of rdoResultset object to create by using the type argument of the OpenResultset method or the ResultsetType property of the RemoteData control. If a type is not specified, the RemoteData control creates a keyset-type rdoResultset. When using RDO to create rdoResultset objects, the default type is forward-only.

Supported Cursor Types

Not all data sources support every type of cursor. The following table summarizes which type of cursor is supported on several typical data sources and on the RemoteData control:


   Data source          Forward-only   Static   Keyset  Dynamic
   ------------------  ------------   -------  ------  -------
   SQL Server 4.2      Yes            Yes/CL    No       No
   SQL Server 6.0
   and above           Yes            Yes       Yes      Yes
   Oracle 7.1          Yes            Yes/CL    No       No
   RemoteData control  No             es        Yes/DD   No

NOTE: CL indicates that support for this cursor is provided by the ODBC cursor library. DD indicates support is provided subject to support by the ODBC driver.

Cursors and the RemoteData Control

Creating an rdoResultset and setting the Resultset property with this new object sets the ResultsetType property of the RemoteData control to the Type property of the new rdoResultset.

NOTE: When using forward-only, read-only result sets, the rdoConnection is held open until the last row of data is accessed. While this can provide performance improvements over other cursors, it can also tie up connection resources.

REFERENCES

Visual Basic online Help
Building Client/Server Applications with Visual Basic

Hitchhiker's Guide to Visual Basic and SQL Server, Microsoft Press.
ISBN: 1-55615-906-4.

Additional query words: kbVBp400 kbVBp500 kbdse kbDSupport kbVBp

Keywords : kbGrpVBDB
Version : WINDOWS:4.0,5.0
Platform : WINDOWS
Issue type : kbhowto