Access Cookbook - Ken Getz [294]
Figure 14-12 shows the properties sheet for a pass-through query to the pubs sample database in SQL Server.
Figure 14-12. Pass-through query properties
The most versatile way to set these properties is to write a procedure that sets them at runtime by using a DAO QueryDef object. You'll then need to set parameter values to the procedure for connection information, the SQL string that comprises the pass-through query, and whether or not the query returns records.
To modify a pass-through query at runtime, follow these general steps:
Open a new module and set a reference to the DAO object library.
Create a new public procedure. Here is the complete code listing:
Public Sub acbPassThrough( _
ByVal QueryName As String, _
ByVal SQLStatement As String, _
Optional ConnectStr As Variant, _
Optional ReturnsRecords As Boolean = True)
Dim qdf As DAO.QueryDef
Dim strConnect As String
Set qdf = CurrentDb.QueryDefs(QueryName)
' If no connection information is supplied,
' connection information from the query is used.
If IsMissing(ConnectStr) Then
strConnect = qdf.Connect
Else
strConnect = CStr(ConnectStr)
End If
' Set query properties to parameter values.
qdf.Connect = strConnect
qdf.ReturnsRecords = ReturnsRecords
qdf.SQL = SQLStatement
ExitHere:
Set qdf = Nothing
Exit Sub
HandleErr:
MsgBox Err & ": " & Err.Description, , "Error in acbPassThrough"
Resume ExitHere
End Sub
To test the procedure, create a new query and choose Query SQL-Specific Pass-through from the menu.
Save the query, naming it qryPassThrough.
Create a form with text boxes and optionally a combo box to test the procedure. The sample form in 14-05.MDB uses the byroyalty stored procedure from the pubs sample database. It takes an input parameter for the royalty percentage. You can change the values on the form shown in Figure 14-13 to adjust any of the arguments needed to call the acbPassThrough procedure.
Figure 14-13. The sample form used to test the acbPassThrough procedure
Write the following code in the Click event of the command button to pass the parameters to acbPassThrough:
Private Sub cmdExecute_Click( )
Dim strQuery As String
Dim strSQL As String
Dim strConnect As String
Dim fReturnsRecs As Boolean
strQuery = Me.lblQuery.Caption
strConnect = Me.lblConnection.Caption
fReturnsRecs = CBool(Me.ckReturnsRecords)
strSQL = "EXEC byroyalty " & Me.cboParameter
Call acbPassThrough(strQuery, strSQL, strConnect, fReturnsRecs)
Me.RecordSource = strQuery
Me.txtAuID.Visible = True
End Sub
Test the procedure by clicking the "Execute byroyalty" command button on the form.
Discussion
The acbPassThrough procedure can modify any saved pass-through query by using the DAO QueryDef object:
Dim qdf As DAO.QueryDef
Dim strConnect As String
Set qdf = CurrentDb.QueryDefs(QueryName)
There is an optional parameter for the ConnectStr argument. If a connection string is not supplied, the one saved with the QueryDef object is used:
If IsMissing(ConnectStr) Then
strConnect = qdf.Connect
Else
strConnect = CStr(ConnectStr)
End If
The properties for the query are then set to the values passed into the procedure:
qdf.Connect = strConnect
qdf.ReturnsRecords = ReturnsRecords
qdf.SQL = SQLStatement
This actually permanently saves changes to the query—if you open the query in design view after executing the procedure, you'll see the last properties that were set.
The values on the form are simply collected from the relevant text boxes and combo boxes, and passed to the procedure. Then the form is requeried and the new results of the pass-through query are loaded as the record source of the form.
Access lets you create ad hoc queries by using the CreateQueryDef syntax and specifying an empty string for the parameter name. However, using a previously saved query eliminates the overhead of creating a new object from scratch and then discarding it.
TIP
The result set returned from a pass-through query is always read-only.
14.6. Pass Parameters to Stored Procedures from