SQL 对数据库连接的整理分类

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Common;
using System.Data.SqlClient;
using System.Data;
using System.Configuration;

namespace classdb
{
    public class dbclass
    {
        SqlConnection conn;
        ///<summary>
        /// 数据库连接
        ///</summary>
        private void ConnectionDb()
        {
            conn = new SqlConnection(ConfigurationManager.AppSettings["ConnectionString "]);
            conn.Open();
        }

        public DataTable PageLoad()
        {
             //方法1的连接方式 不通过 webconfig 获取连接字符
            //创建数据库连接
            //SqlConnection sqlconn = new SqlConnection();
            //填充连接字符串
            //sqlconn.ConnectionString = "server=。;uid=sa;pwd=sasavcv;database=testDB";

            //方法2调用现有的连接方法进行连接
            ConnectionDb();

            //指定sql字符串
            string sql = "select top(10)* from tb1 order by id desc";
            //声明填充Daaset
            DataSet ds = new DataSet();
            //调用适配器
            SqlDataAdapter sa = new SqlDataAdapter(sql, conn);
            //填充表数据
            sa.Fill(ds);
            //返回数据
            return ds.Tables[0];
        }



        ///<summary>
        /// 数据库查询
        ///</summary>
        ///<returns>返回查询字符串</returns>
        private string SelectCommand()
        {
            var strCmd = "select ...";
            try
            {
                SqlCommand sqlComm = new SqlCommand();
                sqlComm.Connection = conn;
                sqlComm.CommandText = strCmd;
                var abc = sqlComm.ExecuteNonQuery();
                if (abc != -1)
                {
                    return "";
                }

                SqlDataReader dataReader = sqlComm.ExecuteReader();
                while (dataReader.Read())
                {
                    return  dataReader["name"] + "\t" + dataReader["time"];
                }
                return "not data!";
            }
            catch (Exception ex)
            {
                return ex.Message;
            }
        }
        ///<summary>
        /// 单个处理的数据库修改
        ///</summary>
        ///<returns></returns>
        private bool UpdateCommand()
        {
            string strCmd = "update ...";
            try
            {
                SqlCommand sqlComm = new SqlCommand();
                sqlComm.Connection = conn;
                sqlComm.CommandText = strCmd;
                sqlComm.ExecuteNonQuery();
                return true;
            }
            catch (Exception ex)
            {
                return false;
            }
        }
        ///<summary>
        /// 综合 修改数据库语句 包含添、删、改
        ///</summary>
        ///<param name="sqlStr"></param>
        ///<returns></returns>
        private int UpdateSql(string sqlStr)
        {
            try
            {
                SqlCommand sqlComm = new SqlCommand();
                sqlComm.Connection = conn;
                sqlComm.CommandText = sqlStr;
               return sqlComm.ExecuteNonQuery();
            }
            catch (Exception ex)
            {
                return -1;
            }
        }
    }
}