//visszateriti a berlesek listajat
        public List<Loan> GetLoanList(string makerFilter, string categoryFilter)
        {
            string query = "SELECT * FROM Berlesek";
            string error = string.Empty;
            SqlDataReader rdr = dal.ExecuteReader(query, ref error);

            List<Loan> loanList = new List<Loan>();
            if (error == "OK")
            {
                while (rdr.Read())
                {
                    Loan v = new Loan();
                    v.LoanID = Convert.ToInt32(rdr[0]);
                    v.VehicleID = Convert.ToInt32(rdr[1]);
                    v.LoanerID = Convert.ToInt32(rdr[2]);
                    v.LoanStart = rdr[3].ToString();
                    v.LoanEnd = rdr[4].ToString();
                    v.Cost = Convert.ToInt32(rdr[5]);

                    loanList.Add(v);
                }
            }
            dal.CloseDataReader(rdr);

            return loanList;
        }
 //hozzaadja az adott autot a kivalasztott datumok kozott a berlesi listahoz
 //ha az mar foglalt valamely napokon a kivalasztott datumok kozott, akkor figyelmezteti a felhasznalot
 private void btnLoanListAdd_Click(object sender, EventArgs e)
 {
     Loan l = new Loan();
     l.LoanStart = dtpLoanStart.Value.ToString("yyyy-MM-dd");
     l.LoanEnd = dtpLoanEnd.Value.ToString("yyyy-MM-dd");
     l.VehicleID = Convert.ToInt32(dgvVehicles.SelectedRows[0].Cells[0].Value);
     if (loans.IsFree(l.VehicleID, l.LoanStart, l.LoanEnd) == 0)
     {
         loanList.Add(l);
         dgvLoanList.Rows.Add(dgvVehicles.SelectedRows[0].Cells[1].Value.ToString() + " " + dgvVehicles.SelectedRows[0].Cells[2].Value.ToString(), dtpLoanStart.Value.ToString("yyyy-MM-dd"), dtpLoanEnd.Value.ToString("yyyy-MM-dd"));
     }
     else
     {
         MessageBox.Show("A jármű foglalt.");
     }
 }