HOWTO: Work w/ Microsoft Access QueryDef Parameter Using VB

ID: Q181782

The information in this article applies to:

ActiveX Data Objects (ADO), versions 1.5, 2.0

SUMMARY

This article contains examples that illustrate how to call a Microsoft Access 97 parameterized QueryDef and return an ADO recordset using Visual Basic version 6.0. Examples are given for both text and numeric input parameters.

MORE INFORMATION

The following examples illustrate ways to return an ADO recordset from a Microsoft Access QueryDef, which expects a parameter in order to return a recordset of one or more rows. The sample application contains three procedures that use Microsoft Access 97 QueryDefs that use parameters.

The first procedure shows an example of passing a numeric parameter while the second procedure shows an example of passing a text parameter. The first two procedures show how to create an ADO parameter collection and define all the parameter properties to have an ADO recordset returned. The third procedure shows how to use the ADO Parameters.Refresh method to return the properties of a parameter.

NOTE: You need to acquire and install the Microsoft Data Access Components (MDAC) version 2.0 for the sample in this article.

The first requirement is to create the Microsoft Access 97 QueryDefs. This article assumes the reader is familiar with creating new QueryDefs in Microsoft Access 97. The following Visual Basic code expects two new QueryDefs in the sample Nwind.mdb included with Visual Basic. Create the new QueryDefs with the following properties:


   Query Name    Table     Criteria      On Field      Datatype
   ------------------------------------------------------------

   ProductsByID  Products  [ProductID]   ProductID     Integer
   CustomerByID  Customers [CustomerID]  CustomerID    Text

Make sure you also set the parameter name and datatype in Microsoft Access 97 by selecting Query, and then choose Parameters.

After the Microsoft Access 97 QueryDef's are created, open a new Visual Basic Project. Form1 is created by default. From the Project menu, choose References then select Microsoft ActiveX Data Objects 1.5 Library.

Follow these steps:

Add three Command buttons to the new form with these settings:


      Button      Name           Caption
      ---------------------------------------------------------

      Command1    cmdNumeric     Numeric Parameter

      Command2    cmdText        Text Parameter

      Command3    cmdParameters  Determine Parameter Properties

Paste the following code into the General Declarations section of Form1:


   Dim Conn As New ADODB.Connection
      Dim Cmd As New ADODB.Command
      Dim Cmd1 As New ADODB.Command
      Dim Cmd2 As New ADODB.Command
      Dim Rs As New ADODB.Recordset

        Private Sub Form_Load()
          Dim strConn As String

          'Change the DSN to match your settings.
            strConn = "DSN=Access97;"
            With Conn
                .CursorLocation = adUseClient
                .ConnectionString = strConn
                .Open
            End With

        End Sub

        Private Sub cmdNumeric_Click()
         'Passes a Numeric parameter to a Microsoft  Access 97 QueryDef
         'that is based on the Products table. The parameter is on the
         'ProductID field.

         With Cmd
           Set .ActiveConnection = Conn
            .CommandText = "Productsbyid"
            .CommandType = adCmdStoredProc

            'ADO Numeric Datatypes are very particular
            .Parameters.Append .CreateParameter("paramProdID", _
                                               adSmallInt, _
                                               adParamInput, _
                                               2) 'Works without a Size
         End With

         Cmd.Parameters("paramProdID") = 3
           'OR
         'Cmd.Parameters(0) = 3
         Rs.Open Cmd, , adOpenStatic, adLockReadOnly

         Debug.Print Rs(0), Rs(1), Rs(2)
         Rs.Close
      End Sub

      Private Sub cmdText_Click()
       'Passes a Text parameter to a Microsoft Access 97 QueryDef that
       'is based on the Customers table. The parameter is on the
       'CustomerID field.

         With Cmd1
           Set .ActiveConnection = Conn
           .CommandText = "Customerbyid"
           .CommandType = adCmdStoredProc

           'Can use either adVarChar or adChar dataType
           .Parameters.Append .CreateParameter("paramCustID", _
                                                adVarChar, _
                                                adParamInput, _
                                                5) 'needs Size to work
         End With

         Cmd1.Parameters("paramCustID") = "COMMI"
         Rs.Open Cmd1, , adOpenStatic, adLockReadOnly

          Debug.Print Rs(0), Rs(1), Rs(2)
          Rs.Close
      End Sub

      Private Sub cmdParameters_Click()
       'The purpose of this procedure is to determine the
       'properties of a parameter.
       '
       With Cmd2
           Set .ActiveConnection = Conn
           .CommandText = "ProductsbyID"
           .CommandType = adCmdStoredProc
       End With
       Cmd2.Parameters.Refresh

       Debug.Print "The parameter properties for ProductsbyID are: " _
        & vbCrLf _
        & "Name: " & Cmd2.Parameters(0).Name & vbCrLf _
        & "Type: " & Cmd2.Parameters(0).Type & vbCrLf _
        & "Direction: " & Cmd2.Parameters(0).Direction & vbCrLf _
        & "Size: " & Cmd2.Parameters(0).Size

        Debug.Print "-------------"

       With Cmd2
           Set .ActiveConnection = Conn
           .CommandText = "CustomerbyID"
           .CommandType = adCmdStoredProc
       End With
       Cmd2.Parameters.Refresh

       Debug.Print "The parameter properties for CustomerbyID are: " _
        & vbCrLf _
        & "Name: " & Cmd2.Parameters(0).Name & vbCrLf _
        & "Type: " & Cmd2.Parameters(0).Type & vbCrLf _
        & "Direction: " & Cmd2.Parameters(0).Direction & vbCrLf _
        & "Size: " & Cmd2.Parameters(0).Size

      End Sub

Run the project, noting the results of each button click.

You may have noticed that another way to get a recordset back from a Microsoft Access QueryDef is to use the Parameter.Refresh method rather than defining the parameter properties in a parameter collection. This actually works although an extra round trip is necessary to the server. However, when passing a text parameter an error occurs because the correct size of a text parameter is not returned by invoking the Parameter.Refresh method. A size property is required when passing a text parameter. This property can be set before creating the ADO recordset to avoid the error.

REFERENCES

For additional information on MDAC 1.5, please see the following article in the Microsoft Knowledge Base:

Q175018 HOWTO: Acquire and Install the Microsoft Oracle ODBC Driver

Additional query words: vbwin kbdse

Keywords : kbAccess kbADO kbADO150 kbADO200 kbVBp
Version : WINDOWS:1.5,2.0
Platform : WINDOWS
Issue type : kbhowto