public List <Pago> ObtenerTodos(int id)
        {
            List <Pago> res = new List <Pago>();

            using (SqlConnection connection = new SqlConnection(connectionString))
            {
                string sql = $"SELECT IdPago, NroPago, Fecha, Importe, ContratoId, c.Monto, c.InquilinoId, c.InmuebleId " +
                             $" FROM Pagos p INNER JOIN Contratos c ON p.ContratoId = c.IdContrato" +
                             $" WHERE IdContrato = @idContrato";

                using (SqlCommand command = new SqlCommand(sql, connection))
                {
                    command.Parameters.Add("@idContrato", SqlDbType.Int).Value = id;
                    command.CommandType = CommandType.Text;
                    connection.Open();
                    var reader = command.ExecuteReader();
                    while (reader.Read())
                    {
                        Pago p = new Pago
                        {
                            IdPago     = reader.GetInt32(0),
                            NroPago    = reader.GetInt32(1),
                            Fecha      = reader.GetDateTime(2),
                            Importe    = reader.GetDecimal(3),
                            ContratoId = reader.GetInt32(4),
                            Alquiler   = new Contrato
                            {
                                IdContrato  = reader.GetInt32(4),
                                Monto       = reader.GetInt32(5),
                                InquilinoId = reader.GetInt32(6),
                                InmuebleId  = reader.GetInt32(7),
                            }
                        };
                        res.Add(p);
                    }
                    connection.Close();
                }
            }
            return(res);
        }
        public int Alta(Pago p)
        {
            int res = -1;

            using (SqlConnection connection = new SqlConnection(connectionString))
            {
                string sql = $"INSERT INTO Pagos (NroPago, Fecha, Importe, ContratoId) " +
                             $"VALUES (@pago, @fecha, @importe, @contratoId);" +
                             $"SELECT SCOPE_IDENTITY();";           //devuelve el id insertado (LAST_INSERT_ID para mysql)
                using (SqlCommand command = new SqlCommand(sql, connection))
                {
                    command.CommandType = CommandType.Text;
                    command.Parameters.AddWithValue("@pago", p.NroPago);
                    command.Parameters.AddWithValue("@fecha", p.Fecha);
                    command.Parameters.AddWithValue("@importe", p.Importe);
                    command.Parameters.AddWithValue("@contratoId", p.ContratoId);
                    connection.Open();
                    res      = Convert.ToInt32(command.ExecuteScalar());
                    p.IdPago = res;
                    connection.Close();
                }
            }
            return(res);
        }
        public int Modificacion(Pago p)
        {
            int res = -1;

            using (SqlConnection connection = new SqlConnection(connectionString))
            {
                string sql = "UPDATE Pagos SET " +
                             "NroPago=@pago, Fecha=@fecha, Importe=@importe, ContratoId=@contratoId " +
                             "WHERE IdPago=@id";
                using (SqlCommand command = new SqlCommand(sql, connection))
                {
                    command.Parameters.AddWithValue("@pago", p.NroPago);
                    command.Parameters.AddWithValue("@fecha", p.Fecha);
                    command.Parameters.AddWithValue("@importe", p.Importe);
                    command.Parameters.AddWithValue("@contratoId", p.ContratoId);
                    command.Parameters.AddWithValue("@id", p.IdPago);
                    command.CommandType = CommandType.Text;
                    connection.Open();
                    res = command.ExecuteNonQuery();
                    connection.Close();
                }
            }
            return(res);
        }