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$Date: 18-Jul-2005 $
$Revision: 0.03 $
$Author: Frank Naudé $
What is VB and what is it used for?
Visual Basic (VB) is an extremely popular and easy to use programming language
provided by Microsoft Corporation. VB is mainly used to develop Windows based
applications with.
DAO - Data Access Objects (1-tier)
Allow VB applications to talk to a database (the JET Engine) via ODBC.
DAO was Microsoft's first object oriented solution for the manipulation of
databases using the Jet Database Engine. The JET engine duplicates the
functionalities of ODBC, and thus does not add much value. As the JET engine
is generic, many of Oracle's features would not be accessible. Microsoft is
phasing out this method.
RDO - Remote Data Objects (2-tier)
Allow VB applications to talk to a relational database (various Relational DBMSs) via ODBC.
RDO is an interface to remote RDBMS via OBDC. One needs the Enterprise Edition of Visual Basic to use RDO.
Microsoft is encouraging developers to migrate their RDO programs to ADO and OLE-DB.
ADO - ActiveX Data Objects (1 to n-tier)
Allow VB/Other Web Tools (Browsers) to interface with different kinds of data sources.
ADO is a more recent Microsoft Data Access technology designed to replace DAO and RDO.
ADO is designed to be simpler to use and more powerful than DAO/RDO.
Serves an interface to Microsoft's new OLE-DB technology (thinner than ODBC).
Can be used to access all sorts of "non traditional data" (e.g., web pages/documents, etc.).
OLE DB data provider
OLE DB is Microsoft's successor to ODBC that utilizes a set of COM interfaces for
accessing and manipulating of data. Oracle implemented OLE DB as part of their
"Oracle Provider for OLE DB" client software.
It provides interface for both data-consuming applications and database providers.
OLE DB is considered a thin middle layer which provides better data access
performance.
Summary
RDO and DAO still works in VB for backwards compatibility. However, it is best
to convert to ADO or OLE-DB.
' DAO Example (Data Access Objects)
Dim wstemp As Workspace
Dim dbtemp As Database
Dim rstemp As Recordset
Set wstemp = DBEngine.Workspaces(0)
Set dbtemp = wstemp.OpenDatabase("", False, False, "ODBC;DSN=Oracle;USR=scott;PWD=tiger")
Set rstemp = dbtemp.OpenRecordset(myquery.Text, dbOpenDynaset, dbSQLPassThrough)
howmany = 0
Combo1.Clear
Do Until rstemp.EOF
msgbox rstemp(0)
rstemp.MoveNext
howmany = howmany + 1
Loop
' RDO Example (Remote Data Objects)
Dim contemp As New rdoConnection
Dim rstemp As rdoResultset
Dim envtemp As rdoEnvironment
Set envtemp = rdoEngine.rdoEnvironments(0)
envtemp.CursorDriver = rdUseServer
' or rdUseOdbc, rdUseNone, rdUseIfNeeded, rdUseClientBatch
With contemp
.Connect = "ODBC;DSN=Oracle;USR=scott;PWD=tiger"
.EstablishConnection rdDriverNoPrompt, false, rdoForwardOnly
' or rdoStatic, rdoKeyset, rdoDynamic
End With
Set rstemp = contemp.OpenResultset("select ...") ' Your SQL here
howmany = 0
With rstemp
Do Until .EOF Or howmany > 2000
msgbox .rdoColumns(0) ' Popup a message box showing the 1st column
.MoveNext
howmany = howmany + 1
Loop
ADO Example
Option Explicit
Public m_adoCnn As New ADODB.Connection
Public m_adoRst As New ADODB.Recordset
Public Sub Command1_Click()
m_adoCnn.ConnectionString = "Provider=MSDAORA;Password=tiger;User ID=scott;Data Source=database"
m_adoCnn.Open
End Sub
Private Sub Form_Unload(Cancel As Integer)
m_adoCnn.Close
End Sub
OO4O Example
Option Explicit
Dim m_oraSession As Object
Dim m_oraDatabase As Object
Private Sub Command1_Click()
Set m_oraSession = CreateObject("OracleInProcServer.XOraSession")
Set m_oraDatabase = m_oraSession.DBOpenDatabase("Database", "user/password", 0&)
MsgBox "Connected to " & m_oraDatabase.Connect & "@" & m_oraDatabase.DatabaseName
End Sub
Private Sub Form_Unload(Cancel As Integer)
Set m_oraDatabase = Nothing
Set m_oraSession = Nothing
End Sub
Dim rs As Recordset rs.MoveLast TxtNumRows.Text = rs.RecordCount
NOTE: Don't forget to do a rs.MoveFirst to get back to the first record again.
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