Proyecto de base de datos Firebird VB

CREATE TABLE universitario(
	id varchar(8) primary key,
	nombre varchar(60),
	mail varchar(60)
);

Imports FirebirdSql.Data.FirebirdClient

Public Class DBData

    Dim Conexion As New FbConnection
    Dim fb_string As FbConnectionStringBuilder = New FbConnectionStringBuilder

    Public Sub conectar()
        ' Se forma la cadena de conexion
        fb_string.ServerType = FbServerType.Default
        fb_string.UserID = "sysdba"
        fb_string.Password = "masterkey"
        fb_string.Dialect = 3
        'ubicacion de la base de datos de firebird
        fb_string.Database = "e:\firebird_db\dbuniv.fdb"
        fb_string.Pooling = False
        ' se realiza la conexion
        Try
            Conexion.ConnectionString = fb_string.ToString
            Conexion.Open()
            If Conexion.State = ConnectionState.Open Then
                Console.WriteLine("Conexión a [" & fb_string.Database & "] establecida")
            End If
        Catch err As FbException
            Console.WriteLine("Error: No se pudo realizar la conexión a [" & fb_string.Database & "]")
            Console.WriteLine(err.Message)
        End Try

    End Sub

    Public Sub Desconectar()
        'si existe conexion abierta, la cierra
        If (ConnectionState.Open) Then
            Conexion.Close()
            Console.WriteLine("Conexión a [" & fb_string.Database & "] cerrada")
        End If
    End Sub

    'realiza una consulta a la base de datos y llena los datos obtenidos en el DataTable
    Public Sub load_data(ByVal dt As DataTable)
        Dim sql As String = "SELECT id,nombre, mail FROM universitario"
        Dim cmd As New FbCommand(sql, Conexion)
        Dim fbdatareader As FbDataReader = cmd.ExecuteReader
        While (fbdatareader.Read)
            Dim s(2) As String
            s(0) = fbdatareader.GetString(0) ' dni
            s(1) = fbdatareader.GetString(1) ' nombre
            s(2) = fbdatareader.GetString(2) 'mail
            dt.Rows.Add(s)
        End While
    End Sub

    'Ejecuta la instruccion INSERT 
    Public Sub insert(ByVal dni As String, ByVal nombre As String, ByVal mail As String)
        Try
            Dim sql As String = "INSERT INTO universitario(id,nombre,mail) " & _
                                "VALUES('" & dni & "','" & nombre & "','" & mail & "')"
            Dim cmd As New FbCommand(sql, Conexion)
            cmd.ExecuteNonQuery()
            cmd = Nothing
        Catch ex As Exception
            Console.WriteLine("Error no se puede ejecutar la instruccion INSERT.")
        End Try

    End Sub

    'Ejecuta la instruccion UPDATE
    Public Sub update(ByVal dni As String, ByVal nombre As String, ByVal mail As String)
        Dim sql As String = "UPDATE universitario SET nombre ='" & nombre & "' , mail='" & mail & "'" & _
                            " WHERE id='" & dni & "' "
        Dim cmd As New FbCommand(sql, Conexion)
        cmd.ExecuteNonQuery()
        cmd = Nothing
    End Sub

    'Ejecuta la instruccion DELETE
    Public Sub delete(ByVal value As String)
        Dim sql As String = "DELETE FROM universitario WHERE id = '" & value & "' "
        Dim cmd As New FbCommand(sql, Conexion)
        cmd.ExecuteNonQuery()
        cmd = Nothing
    End Sub
End Class

Public Class Interfaz

    Dim data As New DBData
    Dim Tabla As New DataTable

    Public Sub New()
        ' This call is required by the Windows Form Designer.
        InitializeComponent()
        'inicia conexion a la base de datos
        data.conectar()
        ' se inicia tabla y datos
        Tabla.Columns.Add("DNI", System.Type.GetType("System.String"))
        Tabla.Columns.Add("Nombre Completo", System.Type.GetType("System.String"))
        Tabla.Columns.Add("Correo Electronico", System.Type.GetType("System.String"))
        'se cargan los datos 
        Actualizar_Tabla()
    End Sub

    Private Sub cmdRegistrar_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdRegistrar.Click
        data.insert(txtDNI.Text, txtNombre.Text, txtMail.Text)
        Actualizar_Tabla()
    End Sub

    Private Sub cmdDelete_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdDelete.Click
        ' cantidad de filas seleccionadas
        Dim selectedRowCount As Integer = DGUniv.Rows.GetRowCount(DataGridViewElementStates.Selected)
        If selectedRowCount > 0 Then
            For i = 0 To selectedRowCount - 1
                'obtiene ubicacion de la fila seleccionada
                Dim index As Integer = DGUniv.SelectedRows(i).Index
                'obtiene el contenido de la fila y celda seleccionda
                Dim selectedDNI As String = DGUniv.Rows(index).Cells(0).Value
                data.delete(selectedDNI)
                Console.WriteLine("Registro eliminado: " & selectedDNI)
            Next
        End If
        Actualizar_Tabla()
    End Sub

    Private Sub Actualizar_Tabla()
        Tabla.Clear()
        data.load_data(Tabla)
        DGUniv.DataSource = Tabla
        DGUniv.Columns(0).Width = 70
        DGUniv.Columns(1).Width = 180
        DGUniv.Columns(2).Width = 180
    End Sub

    Private Sub cmdUpdate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdUpdate.Click
        ' cantidad de filas seleccionadas
        Dim selectedRowCount As Integer = DGUniv.Rows.GetRowCount(DataGridViewElementStates.Selected)
        If selectedRowCount = 1 Then
            'obtiene ubicacion de la fila seleccionada
            Dim index As Integer = DGUniv.SelectedRows(0).Index
            'obtiene el contenido de la fila y celda seleccionda
            Dim selectedDNI As String = DGUniv.Rows(index).Cells(0).Value
            data.update(txtDNI.Text, txtNombre.Text, txtMail.Text)
            Console.WriteLine("Actualizar registro: " & selectedDNI)
        End If
        Actualizar_Tabla()
    End Sub

    Private Sub DGUniv_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles DGUniv.Click
        Dim selectedRowCount As Integer = DGUniv.Rows.GetRowCount(DataGridViewElementStates.Selected)
        If selectedRowCount = 1 Then
            'obtiene ubicacion de la fila seleccionada
            Dim index As Integer = DGUniv.SelectedRows(0).Index
            'Console.WriteLine("registro: " & index)
            'asigna los valores de la fila a los textbox
            txtDNI.Text = DGUniv.Rows(index).Cells(0).Value.ToString
            txtNombre.Text = DGUniv.Rows(index).Cells(1).Value.ToString
            txtMail.Text = DGUniv.Rows(index).Cells(2).Value.ToString
        End If
    End Sub

    Private Sub cmdSalir_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdSalir.Click
        data.Desconectar()
        Application.Exit()
    End Sub
End Class