C# 封装postSQL的添加，查询方法

private static string conns = "PORT=5432;DATABASE=postgres;HOST=localhost;PASSWORD=123456;USER ID=postgres;";
        public static NpgsqlConnection GetConn()
        {
            NpgsqlConnection conn = new NpgsqlConnection(conns);
            //若连接状态是关闭就打开
            Console.WriteLine(conn.State);
            if (conn.State == ConnectionState.Closed)
                conn.Open();
            Console.WriteLine(conn.State);

            return conn;
        }
        public static NpgsqlDataReader Query(string sql,params NpgsqlParameter[] parameters) 
        {
             NpgsqlConnection conn = new NpgsqlConnection(conns);
        conn.Open();

        NpgsqlCommand cmd = new NpgsqlCommand(sql, conn);
        if (parameters != null && parameters.Length > 0)
        {
            cmd.Parameters.AddRange(parameters);
        }

        NpgsqlDataReader reader = cmd.ExecuteReader();

        return reader;
        }
        public static int postSql(string sql) {
            NpgsqlConnection conn = null ;
            try {
                conn = GetConn();
                NpgsqlCommand cmd = new NpgsqlCommand(sql, conn);
                int retule= cmd.ExecuteNonQuery();
                return retule;
            } catch (Exception ex) 
            {
                MessageBox.Show("录入数据失败","警告",MessageBoxButtons.OK,MessageBoxIcon.Error);
                return -1;
            } finally {
                conn.Close();
            }
        }

        //将查询的NpgsqlReader转换为DataTable
        public static DataTable GetDataTable(NpgsqlDataReader reader)
        {
            DataTable table = new DataTable();

            // 添加列
            for (int i = 0; i < reader.FieldCount; i++)
            {
                table.Columns.Add(reader.GetName(i), reader.GetFieldType(i));
            }

            // 添加行
            while (reader.Read())
            {
                object[] values = new object[reader.FieldCount];
                for (int i = 0; i < reader.FieldCount; i++)
                {
                    values[i] = reader.GetValue(i);
                }
                table.Rows.Add(values);
            }

            return table;
        }