尝试从 asp.net Web 服务中的 sql 数据库中读取数据

Question

我一直在尝试从 asp.net Web 服务 .asmx 页面中的本地数据库获取数据，但我只得到一个元素，甚至没有第一个元素。当我尝试另一个索引时，我得到的索引超出了数组异常的范围，但我知道这不是因为我的数据库比我尝试的任何索引都大。

这是我当前的 .asmx 代码

    <%@ WebService Language="C#" Class="PostWebService" %>

using System;
using System.Web;
using System.Web.Services;
using System.Web.Services.Protocols;
using System.Data;
using System.Data.SqlClient;

[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
// To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 
// [System.Web.Script.Services.ScriptService]

public class PostWebService  : System.Web.Services.WebService {
    int result;
    [WebMethod]
    public int GetRates() {
        //try
        //{
            SqlConnection connection = new SqlConnection(@"Data Source = (local); Initial Catalog =  RatesDB; Integrated Security=True");
            SqlCommand cmd = new SqlCommand(" select HeartRate from Rates order by HeartRate DESC", connection);
            connection.Open();
            SqlDataReader dr = cmd.ExecuteReader();
            int i = 0;
            while (dr.Read())
            {
                result = Convert.ToInt32(dr[i++]);
                Console.WriteLine(result);
            }
            dr.Close();
            connection.Close();
        //}
        //finally
        //{ 

        //}
        return result;
    }
}

我一直在使用代码来尝试获得不同的结果，但我不断收到错误：

System.IndexOutOfRangeException: Index was outside the bounds of the array.
   at System.Data.SqlClient.SqlDataReader.CheckDataIsReady(Int32 columnIndex, Boolean allowPartiallyReadColumn, Boolean permitAsync, String methodName)
   at System.Data.SqlClient.SqlDataReader.TryReadColumn(Int32 i, Boolean setTimeout, Boolean allowPartiallyReadColumn)
   at System.Data.SqlClient.SqlDataReader.GetValueInternal(Int32 i)
   at System.Data.SqlClient.SqlDataReader.GetValue(Int32 i)
   at System.Data.SqlClient.SqlDataReader.get_Item(Int32 i)
   at PostWebService.GetRates() in C:\Users\Rommel\Desktop\Website\Website\Website\PostWebService.asmx:line 28

如果我使用 0 作为 dr[0] 的索引，那么我可以读取一个值，但它甚至不是第一个值，所以我不明白为什么它读取我的数据库不正确。任何正确方向的提示，甚至我的代码中的更正都将不胜感激。

Answer 1

获取单个结果（由排序决定）：

public int GetRate()
{
    int i = -1; // an impossible value
    try
    {
        using (SqlConnection connection = new SqlConnection(@"Data Source=(local);Initial Catalog=RatesDB;Integrated Security=True"))
        using (SqlCommand cmd = new SqlCommand(@"select top(1) HeartRate 
                   from Rates 
                   order by HeartRate DESC", connection))
        {
            connection.Open();
            i = Convert.ToInt32(cmd.ExecuteScalar());
            connection.Close();
        }
    }
    catch
    { }
    return result;
}

从一列中获取多个值：

public List<int> GetRates()
{
    var result = new List<int>();
    try
    {
        using (SqlConnection connection = new SqlConnection(@"Data Source=(local);Initial Catalog=RatesDB;Integrated Security=True"))
        using (SqlCommand cmd = new SqlCommand(@"select HeartRate 
                   from Rates 
                   order by HeartRate DESC", connection))
        {
            connection.Open();
            var rdr = cmd.ExecuteReader();
            while (rdr.Read())
            {
                result.Add((int)rdr[0]);
            }
            connection.Close();
        }
    }
    catch
    { }
    return result;
}