[整理]用三层实现ADO.NET的写法（二）

 1.分析功能设计数据库

 2.搭建三层框架
  1).表示层 UI
  2).业务逻辑层 BLL
  3).数据访问层 DAL
  4).实体类库 Models

 3.代码顺序
  1).根据数据库将数据库中的每张表封装成对应的实体类
  2).在UI中添加应用程序配置文件，将数据库连接字符串写在配置文件中
  3).在DAL中写DBHelper类

   using System;using System.Collections.Generic;using System.Text;using System.Data;using System.Data.SqlClient;using System.Configuration;namespace ...DAL{class DBHelper{ static string connectionString = ConfigurationManager.ConnectionStrings["connectionString"].ConnectionString; public static string ConnectionString { get { return DBHelper.connectionString; } } public static int ExecteQuery(string cmdText,CommandType cmdType,params SqlParameter[] parameters) { using (SqlConnection conn=new SqlConnection(connectionString)) { SqlCommand cmd = new SqlCommand(); cmd.CommandText = cmdText; cmd.CommandType = cmdType; cmd.Connection = conn; PrepareCommand(cmd, parameters); try { conn.Open(); return cmd.ExecuteNonQuery(); } catch (Exception ex) { throw ex; } } } public static SqlDataReader ExecuteReader(string cmdText,CommandType cmdType, SqlConnection conn, params SqlParameter[] parameters) { SqlCommand cmd = new SqlCommand(); cmd.CommandText = cmdText; cmd.CommandType = cmdType; cmd.Connection = conn; PrepareCommand(cmd, parameters); try { return cmd.ExecuteReader(); } catch (Exception ex) { throw ex; } } public static object ExecuteScalar(string cmdText, CommandType cmdType, params SqlParameter[] parameters) { using (SqlConnection conn=new SqlConnection(connectionString)) { SqlCommand cmd = new SqlCommand(cmdText, conn); cmd.CommandType = cmdType; PrepareCommand(cmd, parameters); try { conn.Open(); return cmd.ExecuteScalar(); } catch (Exception ex) { throw ex; } } } public static DataTable GetDataTable(string cmdText, CommandType cmdType, params SqlParameter[] parameters) { using (SqlConnection conn=new SqlConnection(connectionString)) { SqlCommand cmd = new SqlCommand(cmdText, conn); cmd.CommandType = cmdType; PrepareCommand(cmd, parameters); SqlDataAdapter da = new SqlDataAdapter(cmd); DataTable dt = new DataTable(); try { da.Fill(dt); return dt; } catch (Exception ex) { throw ex; } } } private static void PrepareCommand(SqlCommand cmd, params SqlParameter[] parameters) { if (parameters != null) { foreach (SqlParameter p in parameters) { cmd.Parameters.Add(p); } } }}}

   4).在DAL中对应每个实体类创建相应的数据访问类，使用DBHelper中的方法实现数据访问
   5).在BLL中对应每个实体类创建相应的业务逻辑类，调用DAL中对应类的方法实现业务逻辑
   6).在UI中调用BLL中的方法实现具体操作