C#、SQL server数据库的连接、增、删、改、查等操作的类

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;
using System.Data;
namespace vote
{
    public class DataBase
    {
        SqlConnection conn;
        //构造连接对象
        //string str = "server=HUZEWEI\\HUZEWEI;database=medicDB;uid=hzw;pwd=198211098";
        public DataBase()
        {
            string str = "server=HUZEWEI\\HUZEWEI;database=medicDB;uid=hzw;pwd=198211098";
            this.conn = new SqlConnection(str);
        }
        //打开连接
        public void open()
        {
            if (conn.State == ConnectionState.Closed)
            {
                conn.Open();
            }
        }
        //关闭当前连接
        public void close()
        {
            if (conn.State == ConnectionState.Open)
            {
                conn.Close();
            }
        }
        //数据表dt
        public DataTable query_dt(string sql)
        {
            close();
            SqlDataAdapter sda = new SqlDataAdapter(sql, conn);
            DataTable dt=new DataTable();
            sda.Fill(dt);
            return dt;
        }
        //设置数据集ds
        public DataSet query_ds(string sql)
        {
            close();
            SqlDataAdapter sda = new SqlDataAdapter(sql, conn);
            DataSet ds = new DataSet();
            sda.Fill(ds);
            return ds;
        }
        //受影响的行数
        public int update(string sql)
        {
            close();
            open();
            SqlCommand sc = new SqlCommand();
            sc.CommandText = sql;
            sc.CommandType = CommandType.Text;
            sc.Connection = conn;
            int x = sc.ExecuteNonQuery();
            close();
            return x;
        }
        //遍历表中的数据
        public SqlDataReader sdread(string sql)
        {
            close();
            SqlDataReader sdr;
            open();
            SqlCommand cmd = new SqlCommand();
            cmd.Connection = conn;
            cmd.CommandText = sql;
            cmd.CommandType = CommandType.Text;
            sdr = cmd.ExecuteReader();
            return sdr;
        }
        //统计表的总数
        public int sum(string sql)
        {
            close();
            open();
            SqlCommand cmd = new SqlCommand();
            cmd.Connection = conn;
            cmd.CommandText = sql;
            cmd.CommandType = CommandType.Text;
            int sum = Convert.ToInt32( cmd.ExecuteScalar());
            close();
            return sum;
        }
        //实例化sqldataadapter对象
        public SqlDataAdapter sqlda(string sql)
        {
            SqlDataAdapter sda = new SqlDataAdapter(sql, conn);
            return sda;
        }
        //更新数据的更改
        public void tbupdate(SqlDataAdapter sda, DataTable dt)
        {
            sda.Fill(dt);
            SqlCommandBuilder scb = new SqlCommandBuilder(sda);
            //执行更新
            sda.Update(dt.GetChanges());
            //使DataTable保存更新
            dt.AcceptChanges();
        }
        //登录密码加密
        public string adpwd(string pwd)
        {
            string s1 = null;
            for (int i = 0; i < pwd.Length; i++)
            {
                s1 += pwd[pwd.Length - i - 1];
            }
            return s1;
        }
    }
}