How To Open ADO Connection and Recordset Objects (168336)

MORE INFORMATION

There are several ways to open a Connection Object within ADO:

• By Setting the ConnectionString property to a valid Connect string and then calling the Open() method. This connection string is provider- dependent.
• By passing a valid Connect string to the first argument of the Open() method.
• By passing a valid Command object into the first argument of a Recordset's Open method.
• By passing the ODBC Data source name and optionally user-id and password to the Connection Object's Open() method.

There are three ways to open a Recordset Object within ADO:

• By opening the Recordset off the Connection.Execute() method.
• By opening the Recordset off the Command.Execute() method.
• By opening the Recordset object without a Connection or Command object, and passing an valid Connect string to the second argument of the Recordset.Open() method.

This code assumes that Nwind.mdb is installed with Visual Basic, and is located in the C:\Program Files\DevStudio\VB directory:

   Option Explicit

   Private Sub cmdOpen_Click()
       Dim Conn1 As New adodb.Connection
       Dim Cmd1 As New adodb.Command
       Dim Errs1 As Errors
       Dim Rs1 As New adodb.Recordset

       Dim i As Integer
       Dim AccessConnect As String

       ' Error Handling Variables
       Dim errLoop As Error
       Dim strTmp As String

       AccessConnect = "Driver={Microsoft Access Driver (*.mdb)};" & _
                     "Dbq=nwind.mdb;" & _
                     "DefaultDir=C:\program files\devstudio\vb;" & _
                     "Uid=Admin;Pwd=;"

       '---------------------------
       ' Connection Object Methods
       '---------------------------

       On Error GoTo AdoError  ' Full Error Handling which traverses
                               ' Connection object

       ' Connection Open method #1:  Open via ConnectionString Property
       Conn1.ConnectionString = AccessConnect
       Conn1.Open
       Conn1.Close
       Conn1.ConnectionString = ""

       ' Connection Open method #2:  Open("[ODBC Connect String]","","")
       Conn1.Open AccessConnect
       Conn1.Close

       ' Connection Open method #3:  Open("DSN","Uid","Pwd")
       Conn1.Open "Driver={Microsoft Access Driver (*.mdb)};" & _
                  "DBQ=nwind.mdb;" & _
                  "DefaultDir=C:\program files\devstudio\vb;" & _
                  "Uid=Admin;Pwd=;"
       Conn1.Close


       '--------------------------
       ' Recordset Object Methods
       '--------------------------

       ' Don't assume that we have a connection object.
       On Error GoTo AdoErrorLite

       ' Recordset Open Method #1:  Open via Connection.Execute(...)
       Conn1.Open AccessConnect
       Set Rs1 = Conn1.Execute("SELECT * FROM Employees")
       Rs1.Close
       Conn1.Close

       ' Recordset Open Method #2:  Open via Command.Execute(...)
       Conn1.ConnectionString = AccessConnect
       Conn1.Open
       Cmd1.ActiveConnection = Conn1
       Cmd1.CommandText = "SELECT * FROM Employees"
       Set Rs1 = Cmd1.Execute
       Rs1.Close
       Conn1.Close
       Conn1.ConnectionString = ""

       ' Recordset Open Method #3:  Open via Command.Execute(...)
       Conn1.ConnectionString = AccessConnect
       Conn1.Open
       Cmd1.ActiveConnection = Conn1
       Cmd1.CommandText = "SELECT * FROM Employees"
       Rs1.Open Cmd1
       Rs1.Close
       Conn1.Close
       Conn1.ConnectionString = ""

       ' Recordset Open Method #4:  Open w/o Connection & w/Connect String
       Rs1.Open "SELECT * FROM Employees", AccessConnect, adOpenForwardOnly
       Rs1.Close

   Done:
       Set Rs1 = Nothing

       Set Cmd1 = Nothing
       Set Conn1 = Nothing

       Exit Sub


   AdoError:
       i = 1
       On Error Resume Next

       ' Enumerate Errors collection and display properties of
       ' each Error object (if Errors Collection is filled out)
       Set Errs1 = Conn1.Errors
       For Each errLoop In Errs1
        With errLoop
           strTmp = strTmp & vbCrLf & "ADO Error # " & i & ":"
           strTmp = strTmp & vbCrLf & "   ADO Error   # " & .Number
           strTmp = strTmp & vbCrLf & "   Description   " & .Description
           strTmp = strTmp & vbCrLf & "   Source        " & .Source
           i = i + 1
        End With
       Next

   AdoErrorLite:
       ' Get VB Error Object's information
       strTmp = strTmp & vbCrLf & "VB Error # " & Str(Err.Number)
       strTmp = strTmp & vbCrLf & "   Generated by " & Err.Source
       strTmp = strTmp & vbCrLf & "   Description  " & Err.Description

       MsgBox strTmp

       ' Clean up gracefully without risking infinite loop in error handler
       On Error GoTo 0
       GoTo Done
   End Sub
				

ERROR NOTES

Only the ADO Connection object has an errors collection. The observant reader will notice that a lightweight error handler is in effect for the RecordSet.Open examples. In the event of an error opening a RecordSet object, ADO should return the most explicit error from the OLEDB provider. Some common errors that can be encountered with the preceding code follow.

If you omit (or there is an error in) the DefaultDir parameter in the connect string, you may receive the following error: If there is an error in the Dbq parameter in the connect string, you may receive the following error: The preceding errors also populate the Connection.Errors collection with the following errors: Note that for each error, the ADO Error number is the same, in this case translating to 0x80004005, which is the generic E_FAIL error message. The underlying Component did not have a specific error number for the condition encountered, but useful information was never-the-less raised to ADO.