using System;

 using System.Collections.Generic;

 using System.Configuration;

 using System.Data.SqlClient;

 using System.Linq;

 using System.Text;

 using System.Threading.Tasks;

 using System.Data;

 namespace Students.DAL

 {

     public class DBHelper

     {

         public static readonly string conn = ConfigurationManager.ConnectionStrings["ClassRoomConnectionString"].ToString();

         public static SqlConnection connection = new SqlConnection(DBHelper.conn);

         /// <summary>

         /// 增删改数据

         /// </summary>

         /// <param name="sql"></param>

         /// <returns></returns>

         public static int ExecuteNonQuery(string sql, SqlParameter[] par)

         {

             try

             {

                 connection.Open();   //打开数据库连接

                 SqlCommand comm = new SqlCommand(sql, connection);

                 //comm.CommandType = System.Data.CommandType.StoredProcedure;

                 comm.Parameters.AddRange(par);

                 return comm.ExecuteNonQuery();

             }

             catch

             {

                 throw;

             }

             finally

             {

                 connection.Close();

             }

         }

         /// <summary>

         /// 增删改数据

         /// </summary>

         /// <param name="sql"></param>

         /// <returns></returns>

         public static int ExecuteNonQuery(string sql, SqlParameter[] par, string sql2, SqlParameter[] par2)

         {

             connection.Open();   //打开数据库连接

             SqlTransaction tra = connection.BeginTransaction();

             try

             {

                 SqlCommand comm = new SqlCommand(sql, connection);

                 SqlCommand comm2 = new SqlCommand(sql2, connection);

                 comm.Parameters.AddRange(par);

                 comm2.Parameters.AddRange(par2);

                 comm.Transaction = tra;

                 comm2.Transaction = tra;

                 int num1 = comm.ExecuteNonQuery();

                 int num2 = comm2.ExecuteNonQuery();

                 int num = comm.ExecuteNonQuery() + comm2.ExecuteNonQuery();

                 tra.Commit();

                 return num;

             }

             catch

             {

                 tra.Rollback();

                 throw;

             }

             finally

             {

                 connection.Close();

             }

         }

         /// <summary>

         /// 查询数据

         /// </summary>

         /// <param name="sql"></param>

         /// <returns></returns>

         public static SqlDataReader ExecuteReader(string sql, SqlParameter[] par)

         {

             try

             {

                 connection.Open();   //打开数据库连接

                 SqlCommand comm = new SqlCommand(sql, connection);

                 //comm.CommandType = System.Data.CommandType.StoredProcedure;

                 comm.Parameters.AddRange(par);

                 return comm.ExecuteReader(CommandBehavior.CloseConnection);

             }

             catch

             {

                 throw;

             }

         }

         /// <summary>

         /// 查询数据

         /// </summary>

         /// <param name="sql"></param>

         /// <returns></returns>

         public static SqlDataReader ExecuteReader(string sql)

         {

             try

             {

                 connection.Open();   //打开数据库连接

                 SqlCommand comm = new SqlCommand(sql, connection);

                 return comm.ExecuteReader(CommandBehavior.CloseConnection);

             }

             catch

             {

                 throw;

             }

         }

         /// <summary>

         /// 返回单个值

         /// </summary>

         /// <param name="sql"></param>

         /// <returns></returns>

         public static object ExecuteScalar(string sql, SqlParameter[] par)

         {

             try

             {

                 connection.Open();   //打开数据库连接

                 SqlCommand comm = new SqlCommand(sql, connection);

                 //comm.CommandType = System.Data.CommandType.StoredProcedure;

                 comm.Parameters.AddRange(par);

                 return comm.ExecuteScalar();

             }

             catch

             {

                 throw;

             }

             finally

             {

                 connection.Close();

             }

         }

     }

 }

 <?xml version="1.0" encoding="utf-8" ?>

 <configuration>

     <startup>

         <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />

     </startup>

   <connectionStrings>

     <add name ="ClassRoomConnectionString"

            connectionString="Data Source=.;Initial Catalog=StudentDB;User ID=sa;Password=sa"

            providerName="System.Data.SqlClient"/>

   </connectionStrings>

 </configuration>