Search through the database using a combobox, if an item is in a database, prompt will appear - vb.net

Question

Good day everyone.
I'm making a POS and Inventory Management System and I'm having a problem with this particular module as of now.
When adding an item to purchase order list, if an item is already in the purchaseorder database, the system will prompt that there is already a pending order. I've done the prompt, but the adding to the database was kinda messed up. It doesn't do a thing at all. The code there is working when I remove the ds.hasrows and while dr.read conditions. This is my code:
Private Sub btnSave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSave.Click
Ceiling = CInt(txtCeiling.Text)
TotalQuantity = CurrentItemQuantity + CInt(txtPurchaseQty.Text)
If TotalQuantity > Ceiling Then
MsgBox("Exceeds Ceiling Point.")
Else
sqlString = "SELECT PRODUCT_ID FROM posinventory.purchaseorder WHERE purchaseorder.PRODUCT_ID = '" & cboProductID.Text & "'"
cmd = New MySqlCommand(sqlString, con)
dr = cmd.ExecuteReader
If dr.HasRows Then
While dr.Read
If CurrentItem = dr.Item("PRODUCT_ID") Then
MsgBox("Product has pending order.")
cboProductID.Focus()
Else
sqlString = "INSERT INTO posinventory.purchaseorder (PRODUCT_ID, PURCHASE_QUANTITY, DATE_PURCHASED, TIME_PURCHASED) VALUES (" & cboProductID.Text & ", '" & txtPurchaseQty.Text & "', '" & txtDate.Text & "', '" & txtTime.Text & "')"
Try
cmd = New MySqlCommand(sqlString, con)
dr = cmd.ExecuteReader
dr.Close()
Catch ex As Exception
MsgBox("Error saving to database. Error is: " & ex.Message)
Exit Sub
End Try
MsgBox("Transaction Complete.")
lvOrderList.Items.Clear()
sqlString = "SELECT posinventory.purchaseorder.TRANSACTION_ID, posinventory.products.PRODUCT_ID, posinventory.products.PRODUCT_NAME, posinventory.products.SUPPLIER_NAME, posinventory.purchaseorder.PURCHASE_QUANTITY, posinventory.purchaseorder.DATE_PURCHASED, posinventory.purchaseorder.TIME_PURCHASED FROM posinventory.purchaseorder, posinventory.products WHERE posinventory.purchaseorder.PRODUCT_ID = posinventory.products.PRODUCT_ID"
cmd = New MySqlCommand(sqlString, con)
da = New MySqlDataAdapter(cmd)
ds = New DataSet
da.Fill(ds, "Table")
Dim i As Integer = 0
Dim j As Integer = 0
For i = 0 To ds.Tables(0).Rows.Count - 1
For j = 0 To ds.Tables(0).Columns.Count - 1
itemcol(j) = ds.Tables(0).Rows(i)(j).ToString()
Next
Dim lvi As New ListViewItem(itemcol)
Me.lvOrderList.Items.Add(lvi)
Next
grpCreateOrder.Enabled = False
grpOrderList.Enabled = True
cboProductID.SelectedIndex = -1
txtPurchaseQty.Text = ""
txtDate.Text = ""
txtTime.Text = ""
txtProductName.Text = ""
txtSupplier.Text = ""
txtQty.Text = ""
txtCeiling.Text = ""
btnBack.Enabled = True
End If
End While
End If
dr.Close()
End If
End Sub

Answer 1

I think its because you are inside of a loop using a cmd and dr. While you are in there you are then defining a new cmd and dr.
Try using different names eg cmd2, dr2.