vb.net call the same function twice from button Event Click - vb.net

Question

This is my code on button event click function
Dim con As New Koneksi
DataGridView1.Rows.Add(con.getIdTambahBarang(cbBarang.Text), _
con.getNamaTambahBarang(cbBarang.Text), _
con.getHargaTambahBarang(cbBarang.Text), _
txtJumlah.Text)
This is my class Koneksi code :
Public Function getIdNamaHargaTambahBarang(ByVal namaBarang As String, ByVal params As String) As String
Dim id As String = ""
Dim nama As String = ""
Dim harga As String = ""
Try
bukaKoneksi()
cmd.Connection = con
cmd.CommandType = CommandType.Text
cmd.CommandText = "SELECT * FROM barang WHERE nama_barang like '" & namaBarang & "'"
reader = cmd.ExecuteReader
If (reader.Read()) Then
If params = "getNama" Then
nama = reader.GetString(1)
Return nama
End If
If params = "getHarga" Then
harga = reader.GetDouble(2).ToString
Return harga
End If
If params = "getId" Then
id = reader.GetString(0)
Return id
End If
End If
tutupKoneksi()
Catch ex As Exception
End Try
End Function
Public Function getIdTambahBarang(ByVal namaBarang As String) As String
Return getIdNamaHargaTambahBarang(namaBarang, "getId")
End Function
Public Function getNamaTambahBarang(ByVal namaBarang As String) As String
Return getIdNamaHargaTambahBarang(namaBarang, "getNama")
End Function
Public Function getHargaTambahBarang(ByVal namaBarang As String) As String
Return getIdNamaHargaTambahBarang(namaBarang, "getHarga")
End Function
Both of the code above, produces
'System.InvalidOperationException' occurred in System.Data.dll error.
When I debug it, the second call of con produces this error. It seems that in VB.NET, the instance class function only can called once at a time, any solution?

Answer 1

Consider refactoring your code. You're actually hitting the database 3 times, each with a LIKE clause, where you really only need to do this once.
Suggest something like this, which performs the same business logic that you've got, with only one call to your database. It's also got some SQL injection prevention.
Dim con As New Koneksi
Dim barang As Barang = Koneksi.GetBarang()
DataGridView1.Rows.Add(barang.id,
barang.nama, _
barang.harga, _
txtJumlah.Text)
Public Class Koneksi
Public Function GetBarang(nama_barang As String)
Dim barang As New Barang
bukaKoneksi()
cmd.Connection = con
cmd.CommandType = CommandType.Text
cmd.CommandText = "SELECT id,name,harga FROM barang WHERE nama_barang = #nama"
cmd.Parameters.AddWithValue("#nama", namaBarang)
reader = cmd.ExecuteReader
If (reader.Read()) Then
barang.id = reader.reader.GetString(0)
barang.nama = reader.GetString(1)
barang.harga = reader.GetDouble(2).ToString
End If
tutupKoneksi()
Return barang
End Function
End Class
You'll retrieve your barang object properties in one statement. All three properties are gathered from the DB at once. When you inevitably want to add another property to your DataGridView, you won't have to make any extra round-trips to your database, but rather only modify your SQL statement, and the .Rows.Add) call.
The database is now safe from SQL injection in this call.
the code is easier to read and understand for the next developer coming into read this code.
the database was previously using more resources due to being called 3x, and using a LIKE clause, where you really only needed an = name.