我想在不使用網格的情況下將 postgres 數據庫中的數據檢索到 C# 中的文本框中。這是我嘗試過使用網格運行成功的代碼：connection.Open();NpgsqlCommand cmd = new NpgsqlCommand();cmd.Connection = connection;cmd.CommandText = "SELECT * FROM student_folio";cmd.CommandType = CommandType.Text;NpgsqlDataAdapter da = new NpgsqlDataAdapter(cmd);DataTable dt = new DataTable();da.Fill(dt);cmd.Dispose();connection.Close();GridView1.DataSource = dt;GridView1.DataBind();當我想將其檢索到文本框中時，構建時出現錯誤：“無法將 [] 索引應用到‘NpgsqlDataAdapter’類型的表達式”這是我的代碼塊：connection.Open();NpgsqlCommand cmd = new NpgsqlCommand();cmd.Connection = connection;cmd.CommandText = ("SELECT f_name FROM student_folio WHERE id = 1");cmd.CommandType = CommandType.Text;NpgsqlDataAdapter da = new NpgsqlDataAdapter(cmd);txtFname.Text = da["f_name"].ToString();cmd.ExecuteNonQuery();cmd.Dispose();connection.Close();