public static ObservableCollection <Let> VratiLetove()
        {
            SqlConnection cnn     = Konekcija.KreirajKoekciju();
            SqlCommand    komanda = new SqlCommand("SELECT * FROM Let WHERE Deleted = 0", cnn);

            ObservableCollection <Let> letovi = new ObservableCollection <Let>();

            try
            {
                cnn.Open();
                SqlDataReader dr = komanda.ExecuteReader();

                while (dr.Read())
                {
                    Let l = new Let();
                    l.Id              = (int)dr["LetId"];
                    l.Sifra           = dr["Sifra"].ToString();
                    l.Pilot           = dr["Pilot"].ToString();
                    l.vremePolaska    = DateTime.Parse(dr["VremePolaska"].ToString());
                    l.vremeDolaska    = DateTime.Parse(dr["VremeDolaska"].ToString());
                    l.PolazniAerodrom = AerodromDAO.vratiAerodrom((int)dr["PolazniAerodrom"]);
                    l.DolazniAerodrom = AerodromDAO.vratiAerodrom((int)dr["DolazniAerodrom"]);
                    l.Avion           = AvionDAO.vratiAvion((int)dr["AvionId"]);
                    l.Cena            = (decimal)dr["Cena"];
                    l.Deleted         = Convert.ToBoolean(dr["Deleted"]);

                    if (l.DolazniAerodrom.Deleted || l.DolazniAerodrom.Naziv == null)
                    {
                        IzbrisiLet(l);
                    }
                    else if (l.PolazniAerodrom.Deleted || l.PolazniAerodrom.Naziv == null)
                    {
                        IzbrisiLet(l);
                    }
                    else if (l.Avion.Deleted || l.Avion == null)
                    {
                        IzbrisiLet(l);
                    }
                    else
                    {
                        letovi.Add(l);
                    }
                }

                cnn.Close();
            }
            catch (Exception xcp)
            {
                if (cnn.State == ConnectionState.Open)
                {
                    cnn.Close();
                }
                MessageBox.Show(xcp.Message);
                return(null);
            }


            return(letovi);
        }
        public static Let vratiLetPrekoSifre(string sifra)
        {
            SqlConnection cnn     = Konekcija.KreirajKoekciju();
            SqlCommand    komanda = new SqlCommand("SELECT * FROM Let WHERE Sifra = @Sifra AND Deleted = 0", cnn);

            komanda.Parameters.AddWithValue("@Sifra", sifra.ToString());
            Let l = new Let();

            try
            {
                cnn.Open();
                SqlDataReader dr = komanda.ExecuteReader();

                while (dr.Read())
                {
                    l.Id              = (int)dr["LetId"];
                    l.Sifra           = dr["Sifra"].ToString();
                    l.Pilot           = dr["Pilot"].ToString();
                    l.vremePolaska    = DateTime.Parse(dr["VremePolaska"].ToString());
                    l.vremeDolaska    = DateTime.Parse(dr["VremeDolaska"].ToString());
                    l.PolazniAerodrom = AerodromDAO.vratiAerodrom((int)dr["PolazniAerodrom"]);
                    l.DolazniAerodrom = AerodromDAO.vratiAerodrom((int)dr["DolazniAerodrom"]);
                    l.Avion           = AvionDAO.vratiAvion((int)dr["AvionId"]);
                    l.Cena            = (decimal)dr["Cena"];
                    l.Deleted         = Convert.ToBoolean(dr["Deleted"]);
                }

                cnn.Close();
            }
            catch (Exception xcp)
            {
                if (cnn.State == ConnectionState.Open)
                {
                    cnn.Close();
                }
                MessageBox.Show(xcp.Message);
                return(null);
            }

            if (l.Id != 0)
            {
                return(l);
            }
            return(null);
        }
        public static ObservableCollection <Let> VratiPovratneLetove(Let let)
        {
            SqlConnection cnn = Konekcija.KreirajKoekciju();
            StringBuilder sb  = new StringBuilder();

            sb.AppendLine("SELECT Let.LetId, Let.Sifra, Let.Pilot,Let.VremePolaska,Let.VremeDolaska, ");
            sb.AppendLine("Let.PolazniAerodrom,Let.DolazniAerodrom,Let.AvionId,Let.Cena,Let.Deleted FROM Let ");
            sb.AppendLine("INNER JOIN Avion ON let.AvionId = Avion.AvionId WHERE ");
            sb.AppendLine("Avion.AvioKompanijaId = @AvioKompanijaId AND Let.PolazniAerodrom = @PolazniAerodrom ");
            sb.AppendLine("AND Let.DolazniAerodrom = @DolazniAerodrom AND Let.Deleted = 0;");

            SqlCommand komanda = new SqlCommand(sb.ToString(), cnn);

            komanda.Parameters.AddWithValue("@AvioKompanijaId", let.Avion.AvioKompanija.Id);
            komanda.Parameters.AddWithValue("@PolazniAerodrom", let.DolazniAerodrom.Id);
            komanda.Parameters.AddWithValue("@DolazniAerodrom", let.PolazniAerodrom.Id);

            ObservableCollection <Let> letovi = new ObservableCollection <Let>();

            try
            {
                cnn.Open();
                SqlDataReader dr = komanda.ExecuteReader();

                while (dr.Read())
                {
                    Let l = new Let();
                    l.Id              = (int)dr["LetId"];
                    l.Sifra           = dr["Sifra"].ToString();
                    l.Pilot           = dr["Pilot"].ToString();
                    l.vremePolaska    = DateTime.Parse(dr["VremePolaska"].ToString());
                    l.vremeDolaska    = DateTime.Parse(dr["VremeDolaska"].ToString());
                    l.PolazniAerodrom = AerodromDAO.vratiAerodrom((int)dr["PolazniAerodrom"]);
                    l.DolazniAerodrom = AerodromDAO.vratiAerodrom((int)dr["DolazniAerodrom"]);
                    l.Avion           = AvionDAO.vratiAvion((int)dr["AvionId"]);
                    l.Cena            = (decimal)dr["Cena"];
                    l.Deleted         = Convert.ToBoolean(dr["Deleted"]);

                    if (l.DolazniAerodrom.Deleted || l.DolazniAerodrom.Naziv == null)
                    {
                        IzbrisiLet(l);
                    }
                    else if (l.PolazniAerodrom.Deleted || l.PolazniAerodrom.Naziv == null)
                    {
                        IzbrisiLet(l);
                    }
                    else if (l.Avion.Deleted || l.Avion == null)
                    {
                        IzbrisiLet(l);
                    }
                    else
                    {
                        letovi.Add(l);
                    }
                }

                cnn.Close();
            }
            catch (Exception xcp)
            {
                if (cnn.State == ConnectionState.Open)
                {
                    cnn.Close();
                }
                MessageBox.Show(xcp.Message);
                return(null);
            }


            return(letovi);
        }