网络方法失败

Question

我在 asmx 页面上有以下 webmethod，但无法连接到我的数据库。任何人都可以阐明我哪里出错了。

[WebMethod]
    public int[] getEmployeeIDs()
    {
        Connection conn = new Connection();
        Recordset rs = new Recordset();
        conn.ConnectionString = "Data Source=MyWebBasedServer;Initial Catalog=MyDatabase;Persist Security Info=False;User ID=MyLogin;Password=MyPassword";
        rs.Open("SELECT ID from MyTable", conn, CursorTypeEnum.adOpenStatic);

        int[] ID = new int[rs.RecordCount];
        int i = 0;
        while (!rs.EOF)
        {
            ID[i++] = rs.Fields["ID"].Value;
            rs.MoveNext();
        }
        rs.Close();
        conn.Close();
        return ID;
    }

我得到的错误信息是

连接不能用于执行此操作。它是 在这种情况下关闭或无效。 （指向“int[] ID = new int[rs.RecordCount];")

谢谢。

Answer 1

下面的代码显示了从 ADO.Net 中的 SELECT 语句中检索结果集的两种常用方法。

有一个名为 ConnectionStrings.com 的网站展示了连接到 SQL Server 的所有各种方式以及许多其他类型的数据库。

如果您是 C# 编程新手，using statement 是在处理实现 IDisposable 的对象时避免资源泄漏的好方法。

从WebMethod 返回复杂类型可能会导致错误。该方法的底层 XML 序列化程序可能不知道如何处理某些类型。在这种情况下，XmlIncludeAttribute 可用于提供显式类型信息。这是一个 MSDN thread 讨论如何去做。

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Web.Services;

namespace ConsoleApplication19
{
  public class Program
  {
    public static void Main(String[] args)
    {
      var connectionString = "Data Source=MyWebBasedServer;Initial Catalog=MyDatabase;Persist Security Info=False;User ID=MyLogin;Password=MyPassword;";
      var a = GetEmployeeIDs_Version1(connectionString);
      var b = GetEmployeeIDs_Version2(connectionString);
    }

    /* Version 1

       Use a "while" loop to fill a WebData list and return it as an array. */

    [WebMethod]
    private static WebData[] GetEmployeeIDs_Version1(String connectionString)
    {
      using (var connection = new SqlConnection(connectionString))
      {
        connection.Open();

        var commandText = "SELECT ID, SurName from MyTable";

        using (var command = new SqlCommand() { Connection = connection, CommandType = CommandType.Text, CommandText = commandText })
        {
          using (var reader = command.ExecuteReader(CommandBehavior.CloseConnection))
          {
            var result = new List<WebData>();

            while (reader.Read())
              result.Add(new WebData() { ID = Convert.ToInt32(reader["ID"]), Surname = reader["Surname"].ToString() });

            return result.ToArray();
          }
        }
      }
    }

    /* Version 2

       Fill a DataSet with the result set.

       Because there's only one SELECT statement, ADO.Net will
       populate a DataTable with that result set and put the
       DataTable in the dataset's Tables collection.

       Use LINQ to convert that table into a WebData array. */

    [WebMethod]
    private static WebData[] GetEmployeeIDs_Version2(String connectionString)
    {
      using (var connection = new SqlConnection(connectionString))
      {
        connection.Open();

        var commandText = "SELECT ID, SurName from MyTable";

        using (var command = new SqlCommand() { Connection = connection, CommandType = CommandType.Text, CommandText = commandText })
        {
          using (var adapter = new SqlDataAdapter())
          {
            var dataSet = new DataSet();
            adapter.SelectCommand = command;
            adapter.Fill(dataSet);

            return
              dataSet
              // There should only be one table in the dataSet's Table's collection.
              .Tables[0]
              .Rows
              // DataTable isn't LINQ-aware.  An explicit cast is needed
              // to allow the use of LINQ methods on the DataTable.Rows collection.
              .Cast<DataRow>()
              // The rows in a DataTable filled by an SqlDataAdapter
              // aren't strongly typed.  All of a row's columns are
              // just plain old System.Object.  Explicit casts are necessary.
              .Select(row => new WebData() { ID = Convert.ToInt32(row["ID"]), Surname = row["Surname"].ToString() })
              // Use LINQ to convert the IEnumerable<WebData> returned by
              // the .Select() method to an WebData[].
              .ToArray();
          }
        }
      }
    }
  }

  public class WebData
  {
    public Int32 ID { get; set; }
    public String Surname { get; set; }
  }
}