Open ADO connection and Recordset objects

This article introduces how to open ADO connection and Recordset objects.

Original product version:   SQL Server
Original KB number:   168336

Summary

ActiveX Data Objects (ADO) offers several ways to open both the Connection and Recordset objects. This article presents sample code for several common techniques for each object.

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 a 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:

ADO Error # -2147467259
Description [Microsoft][ODBC Microsoft Access 97 Driver] '(unknown)'
isn't a valid path. Make sure that the path name is
spelled correctly and that you are connected to the server
on which the file resides.
Source Microsoft OLE DB Provider for ODBC Drivers

If there is an error in the Dbq parameter in the connect string, you may receive the following error:

ADO Error # -2147467259 Description [Microsoft][ODBC Microsoft Access 97 Driver] Couldn't find file '(unknown)'.
Source Microsoft OLE DB Provider for ODBC Drivers

The preceding errors also populate the Connection errors collection with the following errors:

ADO Error # -2147467259
Description [Microsoft][ODBC Driver Manager] Driver's
SQLSetConnectAttr failed
Source Microsoft OLE DB Provider for ODBC Drivers

ADO Error # -2147467259
Description Login Failed
Source Microsoft OLE DB Provider for ODBC Drivers

Note

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.

References

For more information, see Microsoft ActiveX Data Objects (ADO).