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>