c#連接sqlserver

using System;
using System.Collections.Generic;
using System.Web;
using System.Data.OleDb;
using System.Data;
using System.Data.SqlClient;

namespace httpClient.script
{
   public class SqlConnDB
    {
        SqlConnection conn = null; //連接數據庫的對象
                                   /// <summary>
                                   /// 構造函數,連接數據庫，數據庫連接字符在web.Config文件的AppSettings下的conStr
                                   /// </summary>
        public SqlConnDB()
        {
            if (conn == null)
            {
                //判斷連接是否為空
                string conString = "server=(local);database=demo;Trusted_Connection=SSPI";//連接數據庫的字符串
                //string conString = System.Configuration.ConfigurationManager.AppSettings["conStr"];//連接數據庫的字符串
                conn = new SqlConnection(conString);
                if (conn.State == ConnectionState.Closed)
                {
                    conn.Open();//打開數據庫連接
                }
            }
        }
        /// <summary>
        /// 從數據庫中查詢數據的,返回為DataSet
        /// </summary>
        /// <param name="sql"></param>
        /// <returns></returns>
        public DataSet query(string sql)
        {
            DataSet ds = new DataSet();//DataSet是表的集合
            SqlDataAdapter da = new SqlDataAdapter(sql, conn);//從數據庫中查詢
            da.Fill(ds);//將數據填充到DataSet
            connClose();//關閉連接
            return ds;//返回結果
        }
        /// <summary>
        /// 更新數據庫
        /// </summary>
        /// <param name="sql"></param>
        /// <returns></returns>
        public int update(string sql)
        {
            if (conn == null) { return -1; }
            if (conn.State == ConnectionState.Closed)
            {
                conn.Open();//打開數據庫連接
            }
            SqlCommand oc = new SqlCommand();//表示要對數據源執行的SQL語句或存儲過程
            oc.CommandText = sql;//設置命令的文本
            oc.CommandType = CommandType.Text;//設置命令的類型
            oc.Connection = conn;//設置命令的連接
            int x = oc.ExecuteNonQuery();//執行SQL語句
            connClose();//關閉連接
            return x;  //返回一個影響行數
        }
        /// <summary>
        /// 關閉數據庫連接
        /// </summary>
        public void connClose()
        {
            if (conn.State == ConnectionState.Open)
            {
                //判斷數據庫的連接狀態，如果狀態是打開的話就將它關閉
                conn.Close();
            }
        }
    }
}