SqlHelper简单实现（通过Expression和反射）6.Providor模式（工厂+策略）可配置数据库选择

基本思想，将MsSqlDbUtility和MySqlDbUtility设计成单例模式，通过App.config或Web.config进行默认的数据库设置，然后通过DbUtilityFactory获取DbUtility。

1.接口：

  1 using System;
  2 using System.Collections.Generic;
  3 using System.Data;
  4 using System.Linq.Expressions;
  5 using RA.DataAccess.MsSqlDbUtility;
  6 
  7 namespace RA.DataAccess
  8 {
  9     public interface IDbUtility
 10     {
 11         /// <summary>
 12         /// 获取Sql描述对象
 13         /// </summary>
 14         /// <typeparam name="T"></typeparam>
 15         /// <returns></returns>
 16         SqlSession<T> GetSqlExpression<T>() where T : class;
 17         /// <summary>
 18         /// 获取多条数据
 19         /// </summary>
 20         /// <typeparam name="T"></typeparam>
 21         /// <param name="exp"></param>
 22         /// <returns></returns>
 23         List<T> GetList<T>(SqlSession<T> exp) where T : class;
 24         /// <summary>
 25         /// 获取多条数据，并填入DTO中
 26         /// </summary>
 27         /// <typeparam name="Target"></typeparam>
 28         /// <typeparam name="T"></typeparam>
 29         /// <param name="exp"></param>
 30         /// <returns></returns>
 31         List<Target> GetList<Target, T>(SqlSession<T> exp) where T : class where Target : class;
 32         /// <summary>
 33         /// 分页
 34         /// </summary>
 35         /// <typeparam name="T"></typeparam>
 36         /// <param name="By">OrderBy表达式</param>
 37         /// <param name="pageIndex"></param>
 38         /// <param name="pageSize"></param>
 39         /// <returns></returns>
 40         List<T> Paged<T>(Expression<Func<T, object>> By, int pageIndex, int pageSize = 1) where T : class;
 41         /// <summary>
 42         /// 获取单条数据
 43         /// </summary>
 44         /// <typeparam name="T"></typeparam>
 45         /// <param name="func">linq表达式，代表条件</param>
 46         /// <returns></returns>
 47         T GetSingle<T>(Expression<Func<T, bool>> func) where T : class;
 48         /// <summary>
 49         /// 删除一条数据
 50         /// </summary>
 51         /// <typeparam name="T"></typeparam>
 52         /// <param name="func">linq表达式，代表条件</param>
 53         /// <returns></returns>
 54         int Delete<T>(Expression<Func<T, bool>> func) where T : class;
 55         /// <summary>
 56         /// 添加一条数据
 57         /// </summary>
 58         /// <typeparam name="T"></typeparam>
 59         /// <param name="obj"></param>
 60         /// <returns></returns>
 61         int Add<T>(T obj) where T : class;
 62         /// <summary>
 63         /// 直接执行Sql
 64         /// </summary>
 65         /// <typeparam name="T"></typeparam>
 66         /// <param name="sql"></param>
 67         /// <returns></returns>
 68         int RunSingleSql<T>(string sql) where T : class;
 69         /// <summary>
 70         /// 通过Sql获取DataTable，业务层不使用
 71         /// </summary>
 72         /// <typeparam name="T"></typeparam>
 73         /// <param name="sql"></param>
 74         /// <returns></returns>
 75         DataTable GetDataBySql<T>(string sql) where T : class;
 76         /// <summary>
 77         /// 更新一条数据
 78         /// </summary>
 79         /// <typeparam name="T">数据表实体</typeparam>
 80         /// <param name="obj">实体对象</param>
 81         /// <param name="func">linq表达式，代表条件</param>
 82         /// <returns></returns>
 83         int Update<T>(T obj, Expression<Func<T, bool>> func) where T : class;
 84         /// <summary>
 85         /// 添加多条数据
 86         /// </summary>
 87         /// <typeparam name="T"></typeparam>
 88         /// <param name="objs">实体对象列表</param>
 89         /// <returns></returns>
 90         int AddList<T>(List<T> objs) where T : class;
 91         /// <summary>
 92         /// 计数
 93         /// </summary>
 94         /// <typeparam name="T"></typeparam>
 95         /// <param name="func">linq表达式，代表条件</param>
 96         /// <returns></returns>
 97         int Count<T>(Expression<Func<T, bool>> func = null) where T : class;
 98         /// <summary>
 99         /// 获取一个字段数据
100         /// </summary>
101         /// <typeparam name="T"></typeparam>
102         /// <typeparam name="Target"></typeparam>
103         /// <param name="field">linq表达式，代表字段</param>
104         /// <param name="func">linq表达式，代表条件</param>
105         /// <returns></returns>
106         Target Scala<T, Target>(Expression<Func<T, Target>> field, Expression<Func<T, bool>> func);
107     }
108 }

2.工厂类：

 1 using System;
 2 using System.Configuration;
 3 
 4 namespace RA.DataAccess
 5 {
 6     public class DbUtilityFactory
 7     {
 8         public static IDbUtility GetDbUtility()
 9         {
10             var getDbType = ConfigurationManager.AppSettings["DbType"];
11             if (getDbType == "MySql")
12             {
13                 return MySqlDbUtility.DbUtility.GetInstance();
14             }
15             else if (getDbType == "MsSql")
16             {
17                 return MsSqlDbUtility.DbUtility.GetInstance();
18             }
19             else
20             {
21                 throw new NotSupportedException("不支持的数据库");
22             }
23         }
24     }
25 
26 
27 }