ADO1

Jag scemo :p

//classe
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data;
using System.Data.OleDb;

namespace StudentiVoti
{
    class DAL
    {
        private OleDbConnection _conn;

        public DAL()
        {

            string cns = GetConnectionString();
            _conn = new OleDbConnection(cns);
            _conn.Open();
        }

        private string GetConnectionString()
        {
            string dbDirPath = Environment.GetFolderPath(Environment.SpecialFolder.Desktop);
            string cns = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\M_inf3.Quarta\Desktop\StudentiVoti.accdb";
            return cns;
        }

        public DataTable StudentiElenco(string CognomeFiltro)
        {
            DataTable tbl = new DataTable();
            string qry = "SELECT * FROM Studenti WHERE Cognome=?";
            OleDbCommand cmd = new OleDbCommand(qry, _conn);
            cmd.Parameters.AddWithValue("?", CognomeFiltro);
            OleDbDataAdapter dad = new OleDbDataAdapter(cmd);
            dad.Fill(tbl);
            _conn.Close();
            return tbl;
        }

        public DataTable VotiElenco(string IDStudente)
        {
            DataTable tbl = new DataTable();
            string qry = "SELECT * FROM Voti WHERE IDStudente=?";
            OleDbCommand cmd = new OleDbCommand(qry, _conn);
            cmd.Parameters.AddWithValue("?", IDStudente);
            OleDbDataAdapter dad = new OleDbDataAdapter(cmd);
            dad.Fill(tbl);
            _conn.Close();
            return tbl;
        }
    }
}

//classe form

using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace StudentiVoti
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

        }

        private void button1_Click(object sender, EventArgs e)
        {
            DAL c = new DAL();
            dgb1.DataSource = c.VotiElenco(comboBox1.Text);
        }

        private void button2_Click(object sender, EventArgs e)
        {
            DAL c = new DAL();
            dgb2.DataSource = c.StudentiElenco(txtCognome.Text);
        }
    }
}