Question

c#报错：在没有任何数据时进行无效的读取尝试。

下面是连接数据库的代码：
using System.Data;
using System.Data.SqlClient;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ReportOrders
{
class Report
{
static void Main(string[] args)
{
SqlConnection dataConnection = new SqlConnection();
try
{
string username = "sa";
string password = "***";
string connString = String.Format("User ID={0};Password={1};Initial Catalog=ls;" + "Data Source=127.0.0.1", username, password);
dataConnection.ConnectionString = connString;
dataConnection.Open();
Console.Write("输入ID查询ls数据库的实验数据表(5 characters):");
string shiyanId = Console.ReadLine();
Console.WriteLine(shiyanId);
SqlCommand dataCommand = new SqlCommand();
dataCommand.Connection = dataConnection;
dataCommand.CommandType = CommandType.Text;
dataCommand.CommandText = "select ID,列1,列2 from 实验 where ID=@shiyanIdParam";
SqlParameter param = new SqlParameter("@shiyanIdParam", SqlDbType.Int,0);
param.Value = shiyanId;
dataCommand.Parameters.Add(param);
Console.WriteLine("shiyanId的值 {0}\n\n", shiyanId);
SqlDataReader dataReader = dataCommand.ExecuteReader();
string orderId = dataReader.GetString(0);
string lie1 = dataReader.GetString(1);
string lie2 = dataReader.GetString(2);
Console.WriteLine("orderId: {0}列1：{1}列2：{2}", orderId, lie1, lie2);
dataReader.Close();

}
catch (SqlException e)
{
Console.WriteLine("Error accessing the database: {0}", e.Message);
}
finally
{
dataConnection.Close();
}
}
}
}

调试报错：未经处理的异常: System.InvalidOperationException: 在没有任何数据时进行无效的读取尝试。
报错行是：string orderId = dataReader.GetString(0);
请问是怎么回事？
谢谢！！

Answer 1

先要调用dataReader.Read();方法才能对dataReader进行读取操作。
dataReader.Read();
string orderId = dataReader.GetString(0);

Answer 2

SqlDataReader dataReader = dataCommand.ExecuteReader();
while(dataReader.read())
{
string orderId = dataReader.GetString(0);
string lie1 = dataReader.GetString(1);
string lie2 = dataReader.GetString(2);
}
Console.WriteLine("orderId: {0}列1：{1}列2：{2}", orderId, lie1, lie2);
dataReader.Close();

Answer 3

主方法里写那么多代码，没注释