C#连接数据库_使用读取配置文件的方式

 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();
             }
         }
     }
 }

然后再App.config文件中写连接语句

 <?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>