static string conString = "Data Source=.\\SQLEXPRESS;AttachDbFilename="+ System.IO.Directory.GetCurrentDirectory() + "\\ManageSystem.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True";

string commend = "select * from UserInfo where UserId=2";
SqlDataReader sqlDr = Utils.getDataReader(commend);
try
{
if (sqlDr.Read())  //返回json数据，根据字段查找自己需要的信息
{
string userididenity1 = (String)sqlDr["UserIdentity"];
string password = (String)sqlDr["UserPwd"];
}
else
{
MessageBox.Show("用户名不存在");
}
sqlDr.Close();
}
catch
{
MessageBox.Show("数据库连接异常，请重新检查连接，检查你的SQL服务是否为SQLEXPRESS");
}

string str = "insert bookInfo(bookId,bookName,bookAuthor,bookPub,bookContent,bookQuantity) values(" + textBox1.Text + ",‘" + textBox2.Text + "‘,‘" + textBox3.Text + "‘,‘" + textBox4.Text + "‘,‘" + textBox5.Text+" ‘,‘"  + Quantity.Text + "‘)";
                if (Utils.ExecuteNoQuery(str) != -1)
                {
                    MessageBox.Show("添加成功");
                }

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data.SqlClient;
using System.Data;

namespace ManageSystem
{
    static class Utils
    {
        //static string conString ;
        //static SqlConnection sqlcon;
        /*连接mdf*/

         static string conString = "Data Source=.\\SQLEXPRESS;AttachDbFilename="+ System.IO.Directory.GetCurrentDirectory() + "\\ManageSystem.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True";

        static SqlConnection sqlcon = new SqlConnection(conString);



        public static SqlConnection getSqlCon()
        {

            if (sqlcon.State != System.Data.ConnectionState.Open)
            {
                 string dataDir = AppDomain.CurrentDomain.BaseDirectory;


                sqlcon.Open();
                //if (sqlCon.State == System.Data.ConnectionState.Open)
                //    return true;
                //else
                //    return false;

                return sqlcon;
            }
            return sqlcon;


        }

        public static void CreateConnection()
        {

            if (sqlcon.State != System.Data.ConnectionState.Open)
            {
                sqlcon.Open();
            }
            else
            {
                CloseConnection();
                sqlcon.Open();
            }
        }

        public static void CloseConnection()
        {
            sqlcon.Close();
        }

        public static SqlCommand Querry(string strsql)
        {
            try
            {
                CreateConnection();
                SqlCommand sqlcmd = new SqlCommand(strsql, sqlcon);
                sqlcmd.CommandText = strsql;
                return sqlcmd;
            }
            catch
            {
                return null;
            }
        }

        public static SqlDataReader getDataReader(string strsql)
        {
            try
            {
                CreateConnection();
                SqlCommand sqlcmd = new SqlCommand(strsql, sqlcon);
                sqlcmd.CommandText = strsql;
                SqlDataReader sqlDr = sqlcmd.ExecuteReader();
                return sqlDr;
            }
            catch
            {
                return null;
            }
        }
        //执行Insert/update/delete，不带参数
        public static int ExecuteNoQuery(string strsql)
        {
            int i;
            try
            {
                CreateConnection();
                SqlCommand sqlcmd = new SqlCommand(strsql, sqlcon);
                i = sqlcmd.ExecuteNonQuery();
                sqlcon.Close();
                return i;
            }
            catch
            {
                return -1;
            }
        }
        //执行Insert/update/delete，带参数
        public static int ExecuteNoQuery(string strsql, params SqlParameter[] param)
        {
            int i;
            try
            {
                CreateConnection();
                SqlCommand sqlcmd = new SqlCommand(strsql, sqlcon);
                //sqlcmd.Parameters.Add(param);
                foreach (SqlParameter par in param)   //遍历数组将参数对象添加到操作命令中
                {
                    sqlcmd.Parameters.Add(par);
                }
                i = sqlcmd.ExecuteNonQuery();
                return i;
            }
            catch
            {
                return -1;
            }
        }
        public static DataSet GetDataSet(string strsql)
        {
            CreateConnection();
            SqlDataAdapter sda = new SqlDataAdapter(strsql, sqlcon);
            DataSet ds = new DataSet();
            try
            {
                sda.Fill(ds);
                return ds;
            }
            catch
            {
                return null;
            }
        }
        public static DataSet GetDataSet(string strsql, params SqlParameter[] param)
        {
            CreateConnection();
            SqlDataAdapter sda = new SqlDataAdapter(strsql, sqlcon);
            DataSet ds = new DataSet();
            foreach (SqlParameter par in param)
            {
                sda.SelectCommand.Parameters.Add(par);
            }
            try
            {
                sda.Fill(ds);
                return ds;
            }
            catch
            {
                return null;
            }
        }
        public static DataTable GetTable(string strsql)
        {
            try
            {
                CreateConnection();
                SqlDataAdapter sda = new SqlDataAdapter(strsql, sqlcon);
                DataSet ds = new DataSet();
                sda.Fill(ds, "temp");
                sqlcon.Close();
                return ds.Tables["temp"];
            }
            catch
            {
                return null;
            }
        }
        public static DataTable GetTable(string strsql, params SqlParameter[] param)
        {
            try
            {
                CreateConnection();
                string str = strsql;
                SqlDataAdapter sda = new SqlDataAdapter(strsql, sqlcon);
                foreach (SqlParameter par in param)
                {
                    sda.SelectCommand.Parameters.Add(par);
                }
                DataSet ds = new DataSet();
                sda.Fill(ds, "temp");
                sqlcon.Close();
                return ds.Tables["temp"];
            }
            catch
            {
                return null;
            }
        }
    }
}