public int Modificacion(Pago p)
        {
            int res = -1;

            using (SqlConnection connection = new SqlConnection(connectionString))
            {
                string sql = $"UPDATE Pagos SET Monto={p.Monto} , Pagado={p.Pagado}, Fecha='{p.Fecha}', NroPago={p.NroPago}, IdContrato={p.IdContrato} " +
                             $"WHERE IdPago = {p.IdPago} ;";
                using (SqlCommand command = new SqlCommand(sql, connection))
                {
                    command.CommandType = CommandType.Text;
                    connection.Open();
                    res = command.ExecuteNonQuery();
                    connection.Close();
                }
            }
            return(res);
        }
        public int Alta(Pago p)
        {
            int res = -1;

            using (SqlConnection connection = new SqlConnection(connectionString))
            {
                string sql = $"INSERT INTO Pagos (Monto, Pagado, Fecha, NroPago, EstadoPago, IdContrato) " +
                             $"VALUES ({p.Monto}, {p.Pagado}, '{p.Fecha}', {p.NroPago}, 1,  {p.IdContrato}) ;";
                using (SqlCommand command = new SqlCommand(sql, connection))
                {
                    command.CommandType = CommandType.Text;
                    connection.Open();
                    res = command.ExecuteNonQuery();
                    command.CommandText = "SELECT SCOPE_IDENTITY()";
                    var id = command.ExecuteScalar();
                    p.IdPago = Convert.ToInt32(id);
                    connection.Close();
                }
            }
            return(res);
        }