ADO.NET连接数据库DBHelper工具类

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

 using System.Configuration;
 using System.Data;
 using System.Data.SqlClient;

 namespace BookStoreDAL
 {
     public class DBHelper
     {
         private static string connstr = ConfigurationManager.ConnectionStrings["mssqlserver"].ConnectionString;

         //初始化Command对象  和 Connection对象
         public static SqlCommand PrepareCommand(string sql,CommandType cmdType,params SqlParameter[] parameters)
         {
             SqlCommand cmd = new SqlCommand();
             cmd.CommandText = sql;
             cmd.CommandType = cmdType;
             cmd.Connection = new SqlConnection(connstr);
             if (parameters != null)
             {
                 cmd.Parameters.AddRange(parameters);
             }
             cmd.Connection.Open();
             return cmd;
         }
         //通用 增、删、改 方法
         public static int ExecuteNonQuery(string sql,CommandType cmdType,params SqlParameter[] parameters)
         {
             SqlCommand cmd=PrepareCommand(sql,cmdType,parameters);
             int count = cmd.ExecuteNonQuery();
             cmd.Connection.Close();
             return count;
         }

         //查询返回单个值
         public static object ExecuteScalar(string sql, CommandType cmdType, params SqlParameter[] parameters)
         {
             SqlCommand cmd = PrepareCommand(sql, cmdType, parameters);
             object obj = cmd.ExecuteScalar();
             cmd.Connection.Close();
             return obj;
         }

         //查询返回多个值的方法
         public static SqlDataReader ExecuteReader(string sql, CommandType cmdType, params SqlParameter[] parameters)
         {
             SqlCommand cmd = PrepareCommand(sql, cmdType, parameters);
             SqlDataReader reader = cmd.ExecuteReader(CommandBehavior.CloseConnection);
             return reader;
         }
     }
 }