Trying to display a warning message on a btnsubmit_click function in vb.net when the invoice is in use - sql

Question

The sql script is validating the use of the invoice type and invoice. I need to add the check and message in the If (Me.txtMasterId.Text <> "0") method..
Protected Sub btnsubmit_Click(sender As Object, e As EventArgs) Handles btnsubmit.Click
If (Not DataForm.ValidateForm) Then
TransRepo.ModifyStatusName(gUser.CompanyId, Me.txtMasterId.Text, Me.txtStatusName.Text, chkIsPmtPlanFee.Checked, chkIsAttorneyFee.Checked, Me.cboStatus.SelectedValue, Me.txtId.Text, ParseDec(Me.txtExpenseLimit.Text), chkUserSpecPayTo.Checked)
ShowPanel(Me.pnlItemList, Me.Form)
ListOptions(Me.txtMasterId.Text)
SetPageHeader("List Status Name")
If (Me.txtId.Text = "0") Then
ShowConfirmation(Me.lblItemFrmMsg, "New name Added")
If (Me.txtMasterId.Text <> "0") Then
ShowConfirmation(Me.lblItemFrmMsg, "Status Name Saved")
Else
DataForm.DisplayError(Me.lblFrmErr)
End If
End If
End If
End Sub
Dim cn As MySqlConnection
Dim rdr As MySqlDataReader
Try
Dim Sql = "SELECT invoice_type.id
FROM invoice_type_fee
INNER JOIN invoice_name ON invoice_type.id = invoice_type_fee.`id`
WHERE invoice_name.`is_active` = 1
AND invoice_type_fee.`is_active` = 1
AND (invoice_type_fee.`fee_invoice_id` = #invoiceTyID
OR invoice_type_fee.`fee_late_invoicetype_id` = #invoiceTypeID LIMIT 1"
rdr.Read()
If (rdr.HasRows) Then
Dim message As String = "....."
Status.Visible = False
ClientScript.RegisterStartupScript(Me.GetType(), "alert", "alert('" & message & "');", True)
'If (invoicetype = "1") Then
End If
Catch ex As Exception
Throw
End Try
End Sub

Answer 1

There is no reader. You never call ExecuteReader so there's no reader to read. You seem to think that it is Read that executes the SQL but it is not. ExecuteReader executes the SQL and then Read is used to get the data from the result set. I just realised that there isn't even a command in your case. You need to create a command to execute, execute it, then read the results
There's no point getting any data though, because all you care about is whether there is data, not what it is. That means that HasRows is all you need in that case, e.g.
Using connection As New MySqlConnection("connection string here"),
command As New MySqlCommand(sql, connection)
connection.Open()
Using reader = command.ExecuteReader()
If reader.HasRows Then
'The query produced a non-empty result set.
End If
End Using
End Using
A better option would be to add a COUNT to your SQL, call ExecuteScalar and then check whether the result is zero or not.
Dim Sql = "SELECT COUNT(invoice_type.id)
FROM invoice_type_fee
INNER JOIN invoice_name ON invoice_type.id = invoice_type_fee.`id`
WHERE invoice_name.`is_active` = 1
AND invoice_type_fee.`is_active` = 1
AND (invoice_type_fee.`fee_invoice_id` = #invoiceTyID
OR invoice_type_fee.`fee_late_invoicetype_id` = #invoiceTypeID LIMIT 1"
Using connection As New MySqlConnection("connection string here"),
command As New MySqlCommand(sql, connection)
connection.Open()
If CInt(command.ExecuteScalar()) > 0 Then
'There are matching records.
End If
End Using