标签：
第20课-数据库开发及ado.net
可空值类型,资料管理器,多条件查询,Case
SqlHelper
using System;
using System.Collections.Generic;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.Text;
namespace _02省市联动
{
public static class SqlHelper
{
//常量 无法修改
private const string A = "aaa";
//readonly 是一个只读的变量,只能在声明或构造函数中修改
//只读变量只能在构造函数或者是一开始声明变量的时候赋值，不允许在其它地方为变量赋值。
//连接字符串
private static readonly string conStr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
/// <summary>
/// 封装一个ExecuteNonQuery方法,执行insert、delete、updata
/// </summary>
/// <param name="sql"></param>
/// <param name="pms"></param>
/// <returns></returns>
public static int ExecuteQuery(string sql,params SqlParameter[] pms)
{
using (SqlConnection con=new SqlConnection (conStr))
{
using (SqlCommand com=new SqlCommand (sql,con))
{
if (pms!=null)
{
com.Parameters.AddRange(pms);
}
con.Open();
return com.ExecuteNonQuery();
}
}
}
/// <summary>
/// 封装返回一个单个值的方法
/// </summary>
/// <returns></returns>
public static object ExecuteScalar(string sql,params SqlParameter[] pms)
{
using (SqlConnection con = new SqlConnection(conStr))
{
using (SqlCommand com=new SqlCommand (sql,con))
{
if (pms!=null)
{
com.Parameters.AddRange(pms);
}
con.Open();
return com.ExecuteScalar();
}
}
}
/// <summary>
/// 封装一个返回SqlDataReader的方法
/// </summary>
/// <returns></returns>
public static SqlDataReader ExecuteReader(string sql,params SqlParameter[] pms)
{
SqlConnection con=new SqlConnection (conStr);
using (SqlCommand com=new SqlCommand (sql,con))
{
if (pms!=null)
{
com.Parameters.AddRange(pms);
}
try
{
con.Open();
return com.ExecuteReader(System.Data.CommandBehavior.CloseConnection);
}
catch (Exception)
{
con.Close();
con.Dispose();
throw;
}
}
}
public static DataTable ExecuteDataTable(string sql,params SqlParameter[] pms)
{
DataTable dt = new DataTable();
using (SqlDataAdapter adapter=new SqlDataAdapter (sql,conStr ))
{
//如何添加参数
adapter.Fill(dt);
}
return dt;
}
}
}
省市联动
using System;
using System.Collections.Generic;
using System.Text;
namespace _02省市联动
{
public class ProvinceItem
{
public int AreaId {get ;set;}
public string AreaName{get ;set;}
public int AreaPid{get ;set;}
public override string ToString()
{
return this.AreaName;
}
}
}
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
namespace _02省市联动
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
//加载省份信息到第一个ComboBox
LoadProvince();
//设置俩个下拉菜单的默认值为“请选择”
comboBox1.SelectedIndex = 0;
comboBox2.SelectedIndex = 0;
}
private void LoadProvince()
{
string sql = "select * from TblArea where AreaPId =0";
using (SqlDataReader reader=SqlHelper .ExecuteReader(sql))
{
{
if (reader .HasRows)
while(reader .Read())
{
ProvinceItem item = new ProvinceItem();
item.AreaId = reader.GetInt32(0);
item.AreaName = reader.GetString(1);
item.AreaPid = reader.GetInt32(2);
comboBox1.Items.Add(item);
}
}
}
//为ComboBox 增加一个“请选择”
ProvinceItem itemDefault = new ProvinceItem();
itemDefault.AreaId = -1;
itemDefault.AreaName = "请选择";
comboBox1.Items.Insert(0, itemDefault);
}
/// <summary>
/// 下拉菜单的选择项改变事件
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void comboBox1_SelectedValueChanged(object sender, EventArgs e)
{
//获取当前用户选择的项
if (comboBox1.SelectedIndex > 0)
{
//加载第二个下来菜单，数据来源：根据第一个下拉菜单用户选项的AeraId来查询该项的所有子项
//获取当前选中项的ID
ProvinceItem item=comboBox1.SelectedItem as ProvinceItem;
int areaId = item.AreaId;
LoadCity(areaId);
}
}
private void LoadCity(int areaId)
{
comboBox2.Items.Clear();
string sql = "select * from TblArea where AreaPId=@aid";
using (SqlDataReader reader = SqlHelper.ExecuteReader(sql, new SqlParameter("@aid", areaId)))
{
if (reader .HasRows )
{
while (reader.Read())
{
ProvinceItem item = new ProvinceItem();
item.AreaId = reader.GetInt32(0);
item.AreaName = reader.GetString(1);
item.AreaPid = reader.GetInt32(2);
comboBox2.Items.Add(item);
}
}
}
//也添加一个“请选择”
ProvinceItem itemDefault = new ProvinceItem();
itemDefault.AreaId = -1;
itemDefault.AreaName = "请选择";
comboBox2.Items.Insert(0, itemDefault);
comboBox2.SelectedIndex = 0;
}
}
}
第20课-数据库开发及ado.net 可空值类型,资料管理器,多条件查询,Case
标签：
原文地址：http://www.cnblogs.com/Time_1990/p/5862305.html
