Visual Basic Q&A

Symptoms
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.
Resolution
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 ExplicitPrivate Sub cmdOpen_Click()Dim Conn1 As New adodb.ConnectionDim Cmd1 As New adodb.CommandDim Errs1 As ErrorsDim Rs1 As New adodb.RecordsetDim i As IntegerDim AccessConnect As String’ Error Handling VariablesDim errLoop As ErrorDim strTmp As StringAccessConnect = “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 PropertyConn1.ConnectionString = AccessConnectConn1.OpenConn1.CloseConn1.ConnectionString = “”‘ Connection Open method #2:Open(“[ODBC Connect String]“,”",”")Conn1.Open AccessConnectConn1.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 AccessConnectSet Rs1 = Conn1.Execute(“SELECT * FROM Employees”)Rs1.CloseConn1.Close’ Recordset Open Method #2:Open via Command.Execute(…)Conn1.ConnectionString = AccessConnectConn1.OpenCmd1.ActiveConnection = Conn1Cmd1.CommandText = “SELECT * FROM Employees”Set Rs1 = Cmd1.ExecuteRs1.CloseConn1.CloseConn1.ConnectionString = “”‘ Recordset Open Method #3:Open via Command.Execute(…)Conn1.ConnectionString = AccessConnectConn1.OpenCmd1.ActiveConnection = Conn1Cmd1.CommandText = “SELECT * FROM Employees”Rs1.Open Cmd1Rs1.CloseConn1.CloseConn1.ConnectionString = “”‘ Recordset Open Method #4:Open w/o Connection & w/Connect StringRs1.Open “SELECT * FROM Employees”, AccessConnect, adOpenForwardOnlyRs1.CloseDone:Set Rs1 = NothingSet Cmd1 = NothingSet Conn1 = NothingExit SubAdoError:i = 1On Error Resume Next’ Enumerate Errors collection and display properties of’ each Error object (if Errors Collection is filled out)Set Errs1 = Conn1.ErrorsFor Each errLoop In Errs1With errLoopstrTmp = strTmp & vbCrLf & “ADO Error # ” & i & “:”strTmp = strTmp & vbCrLf & “ADO Error# ” & .NumberstrTmp = strTmp & vbCrLf & “Description” & .DescriptionstrTmp = strTmp & vbCrLf & “Source” & .Sourcei = i + 1End WithNextAdoErrorLite:’ Get VB Error Object’s informationstrTmp = strTmp & vbCrLf & “VB Error # ” & Str(Err.Number)strTmp = strTmp & vbCrLf & “Generated by ” & Err.SourcestrTmp = strTmp & vbCrLf & “Description” & Err.DescriptionMsgBox strTmp’ Clean up gracefully without risking infinite loop in error handlerOn Error GoTo 0GoTo DoneEnd 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 that for each error, the ADO Error number is the same, in this case translating to 0×80004005, 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.

Symptoms
When using Microsoft’s Remote Data Control 2.0 (RDC) without a User orSystem DSN in the ODBC Data Source Administrator, trying to set the RDC’sDataSourceName property generates a run-time error.
Resolution
Create a DSN under ODBC or upgrade from MSRDC20.ocx version 5.00.3714 (or5.01.4319), which is “Microsoft Remote Data Control 2.0,” to MSRDC20.ocxversion 6.00.816, which is “Microsoft Remote Data Control 6.0.”

Symptoms
This article demonstrates how to programmatically use Data Links feature of the Microsoft Data Access Components in order to generate a connection string at run-time.
Resolution
In version 2.0 of the Microsoft Data Access Components, Data Links were introduced. Data Link files are similar to ODBC DSN files, but allow you to select an OLE DB provider to connect to your database. With the OLE DB Provider for ODBC drivers, you can also connect to an ODBC data source.
Double-clicking on a Data Link file displays a set of property pages that allow you to build a connection string to connect to your database.
You can use this same functionality in your Visual Basic applications by following the steps listed below: Launch Visual Basic and open a new Standard Exe project. Form1 is created by default.Select References from the Project menu, and then select Microsoft OLE DB Service Component 1.0 Type Library from the list of available references.Add a CommandButton to your form.Add the following code to the Click event of your CommandButton:

Private Sub Command1_Click()Dim objDataLink As New DataLinksDim strConn As StringstrConn = objDataLink.PromptNewMsgBox “The connection string you created is:” & _vbCrLf & strConnEnd Sub Run the project. When you click the CommandButton, you will see the Data Links property pages. Once you have specified how you want to connect to your database and click the OK button, you’ll see the connection string in a dialog box.

Symptoms
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.
Resolution
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 ExplicitPrivate Sub cmdOpen_Click()Dim Conn1 As New adodb.ConnectionDim Cmd1 As New adodb.CommandDim Errs1 As ErrorsDim Rs1 As New adodb.RecordsetDim i As IntegerDim AccessConnect As String’ Error Handling VariablesDim errLoop As ErrorDim strTmp As StringAccessConnect = “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 PropertyConn1.ConnectionString = AccessConnectConn1.OpenConn1.CloseConn1.ConnectionString = “”‘ Connection Open method #2:Open(“[ODBC Connect String]“,”",”")Conn1.Open AccessConnectConn1.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 AccessConnectSet Rs1 = Conn1.Execute(“SELECT * FROM Employees”)Rs1.CloseConn1.Close’ Recordset Open Method #2:Open via Command.Execute(…)Conn1.ConnectionString = AccessConnectConn1.OpenCmd1.ActiveConnection = Conn1Cmd1.CommandText = “SELECT * FROM Employees”Set Rs1 = Cmd1.ExecuteRs1.CloseConn1.CloseConn1.ConnectionString = “”‘ Recordset Open Method #3:Open via Command.Execute(…)Conn1.ConnectionString = AccessConnectConn1.OpenCmd1.ActiveConnection = Conn1Cmd1.CommandText = “SELECT * FROM Employees”Rs1.Open Cmd1Rs1.CloseConn1.CloseConn1.ConnectionString = “”‘ Recordset Open Method #4:Open w/o Connection & w/Connect StringRs1.Open “SELECT * FROM Employees”, AccessConnect, adOpenForwardOnlyRs1.CloseDone:Set Rs1 = NothingSet Cmd1 = NothingSet Conn1 = NothingExit SubAdoError:i = 1On Error Resume Next’ Enumerate Errors collection and display properties of’ each Error object (if Errors Collection is filled out)Set Errs1 = Conn1.ErrorsFor Each errLoop In Errs1With errLoopstrTmp = strTmp & vbCrLf & “ADO Error # ” & i & “:”strTmp = strTmp & vbCrLf & “ADO Error# ” & .NumberstrTmp = strTmp & vbCrLf & “Description” & .DescriptionstrTmp = strTmp & vbCrLf & “Source” & .Sourcei = i + 1End WithNextAdoErrorLite:’ Get VB Error Object’s informationstrTmp = strTmp & vbCrLf & “VB Error # ” & Str(Err.Number)strTmp = strTmp & vbCrLf & “Generated by ” & Err.SourcestrTmp = strTmp & vbCrLf & “Description” & Err.DescriptionMsgBox strTmp’ Clean up gracefully without risking infinite loop in error handlerOn Error GoTo 0GoTo DoneEnd 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 that for each error, the ADO Error number is the same, in this case translating to 0×80004005, 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.

Symptoms
A Visual Basic for Applications procedure that uses ODBCDirect to createand populate a table in another Microsoft Access database also createscorrupted unique indexes in that table. This behavior occurs if theprocedure performs the following steps in sequence:BeginTrans on the ODBCDirect workspaceExecute method on a connection to Create Table with Unique IndexesExecute method on the connection to Append records to that tableExecute method on the connection to Update the newly added recordsCommitTrans on the ODBCDirect workspaceIf you modify data in a field that is a unique index in the resulting tablebut is not a primary key, you receive the following error message when youtry to commit the record:

Reserved Error (-1601); there is no message for this error.You are able to make changes to data in other fields.
This behavior occurs when the ODBC data source is a Microsoft Access 97database or a Microsoft Access version 7.0 database.
This behavior also occurs if you use Remote Data Object (RDO) instead ofODBCDirect in the Enterprise Edition of Microsoft Visual Basic version 4.0.
This article assumes that you are familiar with Visual Basic forApplications and with creating Microsoft Access applications using theprogramming tools provided with Microsoft Access. For more informationabout Visual Basic for Applications, please refer to the “BuildingApplications with Microsoft Access 97″ manual.
Resolution
If you have already created the table and are unable to enter data becauseunique indexes are corrupted, press ESC to cancel the changes to therecord. Then compact the database. After you have compacted the database,you can make changes to the data in the unique index fields.
There are three methods to prevent the corruption from occurring.
Method 1The recommended resolution is to use a Microsoft Jet workspace rather thanan ODBCDirect workspace to create and modify the table. When you use anODBCDirect workspace to modify a Microsoft Jet database, data accessobjects (DAO) loads the Microsoft Jet ODBC driver, which in turn loadsMicrosoft Jet. A procedure in which DAO creates and modifies the tabledirectly without going through ODBC is more efficient.
Method 2Commit the transaction after you have created the table but before youappend the records, or after you have appended the records but before youmodify them.
Method 3If you must create the table, append the records and modify the recordswithin a single transaction, create the unique indexes by executing an SQLstatement that is separate from the SQL statement that creates the table.Note that you can create a primary key in the same SQL statement thatcreates the table; although other unique indexes become corrupted, aprimary index does not become corrupted.
The following example contains a procedure that creates the table, appendsthe records, and modifies the records within a single transaction.Create a blank database in Microsoft Access version 7.0 or 97.Create an ODBC DSN whose data source is the database created in Step 1, and name it “TestRDO97″ (without the quotation marks).Create a blank database in Microsoft Access 97.Create a module and type the following line in the Declarationssection if it is not already there:

Option Explicit Type the following procedure:

Sub CreateIndexTrans (strTableName as string, strDSN as string)Dim Connection1 As Connection, ws As WorkspaceOn Error GoTo ErrorhandlerSet ws = DBEngine.CreateWorkspace _(“TransAct”, “Admin”, “”, dbUseODBC)Set Connection1 = ws.OpenConnection(“Con1″, _dbDriverCompleteRequired, , “ODBC;DSN=” & strDSN)ws.BeginTransConnection1.Execute “CREATE TABLE ” & strTableName & _” (ID INTEGER constraint ID PRIMARY KEY, ” & _”LastName Text (50), FirstName Text (50), keyCode ” & _”Text (10), SSN Text (20))”‘———– Create Indexes ——————Connection1.Execute “CREATE INDEX ” & _”idxLastName ON ” & strTableName & ” (LastName)”Connection1.Execute “CREATE UNIQUE INDEX ” & _”idxKeyCode ON ” & strTableName & ” (KeyCode)”Connection1.Execute “CREATE UNIQUE INDEX ” & _”idxSSN ON ” & strTableName & ” (SSN)”‘———————————————Connection1.Execute “INSERT INTO ” & strTableName & _” (ID, FirstName, LastName, KeyCode, SSN) ” & _”Values (1, ‘Bob’, ‘Wire’, ‘ABC’,'012-34-5678′)”Connection1.Execute “UPDATE ” & strTableName & _” SET FirstName = ‘Robert’, LastName=’Wires’, ” & _”KeyCode=’A1B1C1′, SSN=’987-65-4321′ WHERE ID = 1″ws.CommitTransConnection1.CloseMsgBox strTableName & ” created in other database.”Exit_CreateIndexProblem:Exit SubErrorhandler:MsgBox CStr(Err) & ” ” & Err.DescriptionResume Exit_CreateIndexProblemEnd Sub To run this subroutine, type the following line in the Debug window,and then press ENTER:
CreateIndexTrans “tblIndexTrans”, “TestRDO97″Open the database you created in Step 1.Open tblIndexTrans.Change the data in the keyCode field or in the SSN field. Note that you can successfully commit the record.