从一个舆论调查的制作谈面向对象的编程思路（二）

首先，我们要来定义一个数据库表，以保存舆论调查的想关数据，看下面这个表：
/*新闻调查表*/
if exists(select * from sysobjects where id = object_id('Survey'))
drop table Survey
go

create table Survey
(
ID int identity Primary key not null ,
SurveyID varchar(20) default "" not null ,
Kind tinyint default 0 not null ,
Title nvarchar(100) default "" not null ,
Description nvarchar(255) default "" not null ,
Amount int default 0 not null ,
BeginTime datetime default getdate() not null ,
EndTime datetime default getdate() not null ,
Active bit default 0 not null
)
go

好了，数据库建好了，我可以从上面的survey基类中继承出具体的子类，比如说我现在要做一个同足球相

关的调查，那就做这么一个类：

namespace Football
{
using System;
using MyClass.Util ;
using System.Data.SQL ;
using System.Collections ;
/// <summary>
/// 足球舆论调查
/// </summary>
/// <remarks>
/// 从MyClass.Util.Survey类继承而来
/// </remarks>
public class FootballSurvey : MyClass.Util.Survey
{

public FootballSurvey()
{
}

/// <summary>
/// 重载父类虚函数
/// </summary>
/// <param name="a_intID">该调查的数据库id </param>
public override void LoadFromDatabase(string a_strID)
{
MyClass.Util.MyConnection myConn = new MyConnection() ;
SQLCommand myCommand = new SQLCommand() ;
myCommand.CommandText = "up_GetSurvey" ;
myCommand.CommandType = System.Data.CommandType.StoredProcedure ;

try
{
myConn.Open() ;
myCommand.ActiveConnection = myConn ;
myCommand.Parameters.Add(new SQLParameter("@a_strsurveyid" ,

SQLDataType.VarChar , 20)) ;
myCommand.Parameters["@a_strsurveyid"].Value = a_strID ;
SQLDataReader myReader ;
myCommand.Execute(out myReader) ;

//先取调查
if (myReader.Read())
{
this.m_strTitle = myReader["title"].ToString() ;
this.m_intHits = (int)myReader["amount"] ;
this.m_strID = a_strID ;
this.m_datBeginTime =

(DateTime)myReader["begintime"] ;
this.m_datEndTime = (DateTime)myReader["endtime"] ;
}
else
{
throw(new Exception("数据库中无此调查的纪录")) ;
}

//清空调查项
m_arrItems.Clear() ;

//取调查项
if (myReader.HasMoreRows)
{
while(myReader.Read())
{
SurveyItem item = new SurveyItem() ;
item.Text = myReader["title"].ToString() ;
item.ID = (int)myReader["id"] ;
item.Count = (int)myReader["amount"] ;
item.Description =

myReader["Description"].ToString() ;
AddItem(item) ;
}
}
else
{
throw(new Exception("数据库中没有该调查相关的调查项

")) ;
}

//清场
myReader.Close() ;
myConn.Close() ;
}
catch(Exception e)
{
throw(new Exception("从数据库中读取调查失败：" +

e.ToString())) ;
}
}

/// <summary>
/// 将调查保存到数据库
/// </summary>
/// <param name="m_strSurveyID">调查编号 </param>
/// <remarks>
/// 如果m_strSurveyID不为空，则删除原纪录，用当前调查编号保存新的调查，
/// 否则就生成一个新的调查编号
/// </remarks>
public override void SaveToDatabase(string m_strSurveyID)
{
//如果没有标题或调查项则抛出异常
if (this.m_arrItems.Count == 0 || this.m_strTitle == "")
{
throw(new Exception("没有调查标题或标题项")) ;
}

MyClass.Util.MyConnection myConn = new MyConnection() ;
SQLCommand myCommand = new SQLCommand() ;
myCommand.CommandType = System.Data.CommandType.Text ;

try
{
myConn.Open() ;
myCommand.ActiveConnection = myConn ;

//如果没有surveyid则生成surveyid
string strSurveyID ;
if(m_strSurveyID == "")
{
strSurveyID = DateTime.Now.Year.ToString()
+

DateTime.Now.Month.ToString()
+

DateTime.Now.Hour.ToString()
+

DateTime.Now.Minute.ToString()
+

DateTime.Now.Second.ToString()
+

DateTime.Now.Millisecond.ToString() ;
}
else //如果已有，则删除该条纪录
{
strSurveyID = m_strSurveyID ;
//删除原有纪录
myCommand.CommandText = "delete from survey where

surveyid='" + strSurveyID + "'" ;
myCommand.ExecuteNonQuery() ;
}

string strSql = "insert into survey(surveyid , kind , title)

values ('"
+ strSurveyID +"', 0 , '" +

m_strTitle + "')/r/n" ;
for (int i = 0 ; i < m_arrItems.Count ; i ++)
{
strSql += "insert into survey(surveyid , kind ,

title) values('"
+ strSurveyID + "' , 1 , '"
+ ((SurveyItem)m_arrItems[i]).Text +

"')/r/n" ;
}
//插库
myCommand.CommandText = strSql ;
myCommand.ExecuteNonQuery() ;

//清场
myConn.Close() ;
}
catch(Exception e)
{
throw(new Exception("保存调查时出错：" + e.ToString())) ;
}

}

/// <summary>
/// 投票
/// </summary>
/// <param name="a_intID"> </param>
public override void Vote(int a_intID)
{
//该项计数加一
((SurveyItem)m_arrItems[a_intID]).Count += 1 ;

//数据库中改变
MyConnection myConn = new MyConnection() ;
SQLCommand myCommand = new SQLCommand() ;
myCommand.CommandText = "update survey set amount=amount+1 where

id="
+

((SurveyItem)m_arrItems[a_intID]).ID.ToString() ;

myCommand.CommandType = System.Data.CommandType.Text ;

try
{
myConn.Open() ;
myCommand.ActiveConnection = myConn ;
myCommand.ExecuteNonQuery() ;
myConn.Close() ;
}
catch(Exception e)
{
throw(new Exception("更新调查项失败:" + e.ToString())) ;
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