.Net 6: C# で PostgreSQL の Update

プロジェクトの作成

mkdir Update01
cd Update01
dotnet new console
dotnet add package Npgsql --version 7.0.0-preview.6

フォルダー構造

$ tree -L 1
.
├── Program.cs
├── Update01.csproj
└── obj

Program.cs

// ----------------------------------------------------------------
/*
	Program.cs

					Aug/09/2022

*/
// ----------------------------------------------------------------
using System;
using System.Data;
using System.Text;
using Npgsql;

// ----------------------------------------------------------------
public static class postgres_update
{
// ----------------------------------------------------------------
static async Task Main (string[] args)
{
	Console.WriteLine ("*** 開始 ***");
	string	id_in = args[0];
	int	population_in = int.Parse (args[1]);

	string server="localhost";
	string str_db="city";

	string user="scott";
	string password="tiger123";

	string str_connect = "Host=" + server + ";Username="
		+ user + ";Password="
		+ password + ";Database=" + str_db + ";";

	await using var conn = new NpgsqlConnection(str_connect);
	await conn.OpenAsync();

	update_proc(conn,id_in,population_in);

	Console.WriteLine ("*** 終了 ***");
}

// ----------------------------------------------------------------
static void update_proc
	(NpgsqlConnection connection,string id_a,int population_a)
{
	DateTime dateNow = DateTime.Now;

	string str_date = dateNow.ToString("yyyy-MM-dd HH:mm:ss");
	Console.WriteLine (str_date);

	StringBuilder sb_sql = new StringBuilder
			("UPDATE cities SET population = "
			+ population_a + @" , date_mod = '" + str_date +
			@"' WHERE id = '" + id_a + "'");

	string str_sql = sb_sql.ToString ();

	Console.WriteLine (str_sql);

	NpgsqlCommand command = new NpgsqlCommand (str_sql,connection);
	int rowsAffected = command.ExecuteNonQuery ();
	Console.WriteLine ("rowsAffected = " + rowsAffected);
}

// ----------------------------------------------------------------
}
// ----------------------------------------------------------------

実行結果

$ dotnet run t3466 8932100
*** 開始 ***
2022-08-09 20:04:38
UPDATE cities SET population = 8932100 , date_mod = '2022-08-09 20:04:38' WHERE id = 't3466'
rowsAffected = 1
*** 終了 ***