基于NXBRE规则引擎实现的柔性折扣策略

　　规则引擎由推理引擎发展而来，是一种嵌入在应用程序中的组件，实现了将业务决策从应用程序代码中分离出来，并使用预定义的语义模块编写业务决策。接受数据输入，解释业务规则，并根据业务规则做出业务决策。应用背景： 企业级管理者对企业IT系统的开发有着如下的要求：

1. 为提高效率，管理流程必须自动化，即使现代商业规则异常复杂。

2. 市场要求业务规则经常变化，IT系统必须依据业务规则的变化快速、低成本的更新。

3. 为了快速、低成本的更新，业务人员应能直接管理IT系统中的规则，不需要程序开发人员参与。

　　下面介绍一个开源的引擎（NXBRE  Rule-engine）实现动态折扣价格计算：

　　折扣逻辑配置使用XML（扩展名.xbre）为文件，后期修改XML打折策略，在程序代码无需修改的情况，实现柔性折扣策略的目的。

　　折扣规则文件：discount.xbre 

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <xBusinessRules xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="xBusinessRules.xsd">
 3     <!-- 全局变量-->
 4     <Integer id="10i" value="10"/>
 5     <Integer id="40i" value="40"/>  
 6     <ObjectLookup id="QuantityOrdered" objectId="CurrentOrder" member="Quantity"/>
 7     <Logic>
 8         <If>
 9             <And>
10                 <GreaterThanEqualTo leftId="ClientRating" rightId="ClientRatingThreshold">
11                       <!-- CurrentOrder为订单对象-->
12                     <ObjectLookup id="ClientRating" objectId="CurrentOrder" member="ClientRating"/>
13                     <String id="ClientRatingThreshold" value="C"/>
14                 </GreaterThanEqualTo>
15             </And>
16             <Do>
17                 <!-- 对于评分高的客户指定的折扣策略 Discount rules for high rate customers -->
18                 <Logic>
19                     <If>
20                         <And>
21                             <GreaterThan leftId="QuantityOrdered" rightId="40i"/>
22                         </And>
23                         <Do>
24                           <!-- AppliedDiscount为应用的折扣-->
25                             <Evaluate id="AppliedDiscount">
26                               <!-- Percent为折扣比例-->
27                                 <Parameter name="Percent" value=".7"/>
28                             </Evaluate>
29                         </Do>
30                     </If>
31                     <ElseIf>
32                         <And>
33                             <GreaterThan leftId="QuantityOrdered" rightId="10i"/>
34                         </And>
35                         <Do>
36                             <Evaluate id="AppliedDiscount">
37                                 <Parameter name="Percent" value=".8"/>
38                             </Evaluate>
39                         </Do>
40                     </ElseIf>
41                     <Else>
42                         <Evaluate id="AppliedDiscount">
43                             <Parameter name="Percent" value=".9"/>
44                         </Evaluate>
45                     </Else>
46                 </Logic>
47             </Do>
48         </If>
49         <Else>
50             <!-- 对于评分低的客户指定的折扣策略 Discount rules for low rate customers -->
51             <Logic>
52                 <If>
53                     <And>
54                         <GreaterThan leftId="QuantityOrdered" rightId="40i"/>
55                     </And>
56                     <Do>
57                         <Evaluate id="AppliedDiscount">
58                             <Parameter name="Percent" value=".9"/>
59                         </Evaluate>
60                     </Do>
61                 </If>
62                 <Else>
63                     <Evaluate id="AppliedDiscount">
64                         <Parameter name="Percent" value="1"/>
65                     </Evaluate>
66                 </Else>
67             </Logic>
68         </Else>
69     </Logic>
70 </xBusinessRules>

　　所有的业务逻辑都在discount.xbre 中定义，下面我们定义一个窗体来解析折扣逻辑并显示计算的结果：

  1 using System;
  2 using System.Collections.Generic;
  3 using System.ComponentModel;
  4 using System.Data;
  5 using System.Drawing;
  6 using System.Linq;
  7 using System.Text;
  8 using System.Threading.Tasks;
  9 using System.Windows.Forms;
 10 using System.Collections;
 11 using NxBRE.FlowEngine;
 12 using NxBRE.FlowEngine.IO;
 13 using BREFactory = NxBRE.FlowEngine.Factories.BREFactory;
 14 using Reflection = NxBRE.Util.Reflection;
 15 namespace WinApp
 16 {
 17     public partial class frmDiscountRBE : Form
 18     {
 19         public frmDiscountRBE()
 20         {
 21             InitializeComponent();
 22 
 23         }
 24       
 25         /// <summary>
 26         /// 规则xml文件名称
 27         /// </summary>
 28         public const string FLOW_RULES_FILENAME = "discount.xbre";
 29         public const string ORDER = "CurrentOrder";
 30         public const string APPLIED_DISCOUNT = "AppliedDiscount";
 31         public const string PERCENT = "Percent";
 32         /**/
 33         /// <summary>
 34         /// 定单
 35         /// </summary>
 36         struct Order
 37         {
 38             public Int32 Quantity;
 39             public Double TotalCost;
 40             public string ClientRating;
 41             public Order(int _q, double _t, string _c)
 42             {
 43                 this.Quantity = _q;
 44                 this.TotalCost = _t;
 45                 this.ClientRating = _c;
 46             }
 47         }
 48         /**/
 49         /// <summary>
 50         /// 计算结果
 51         /// </summary>
 52         /// <param name="aBRC">规则引挚上下文</param>
 53         /// <param name="aMap"></param>
 54         /// <param name="aStep"></param>
 55         /// <returns>结果</returns>
 56         static object AppliedDiscount(IBRERuleContext aBRC, IDictionary aMap, object aStep)
 57         {
 58             Order _order = (Order)aBRC.GetObject(ORDER);
 59             double _d = Convert.ToDouble(Reflection.CastValue(aMap[PERCENT], typeof(double)));
 60             return _order.TotalCost * _d;
 61         }
 62         private void btnDiscount_Click(object sender, EventArgs e)
 63         {
 64             try
 65             {
 66                 //载入规则
 67                 IRulesDriver rulesDriver = new XBusinessRulesFileDriver(FLOW_RULES_FILENAME);
 68                 //工厂
 69                 BREFactory breFactory = new BREFactory();
 70                 //引挚实例
 71                 IFlowEngine bre = breFactory.NewBRE(rulesDriver);
 72                 //委托实例
 73                 ExecuteRuleDelegate executeRuleDelegate = new ExecuteRuleDelegate(AppliedDiscount);
 74                 bre.RuleContext.SetFactory(APPLIED_DISCOUNT, new BRERuleFactory(executeRuleDelegate));
 75                 //设置规则引挚环境变量
 76                 //Order order = new Order(5, 25, "A");
 77                 Order order = new Order(Int32.Parse(this.txtQuantity.Text), Double.Parse(this.txtTotalCost.Text), this.txtClientRating.Text);
 78                 bre.RuleContext.SetObject(ORDER, order);
 79                 //执行
 80                 bre.Process();
 81                 //得到执行结果
 82                 double result = (double)bre.RuleContext.GetResult(APPLIED_DISCOUNT).Result;
 83 
 84                 this.txtPayCost.Text = result.ToString();
 85                 this.txtPayCost.ReadOnly = true;
 86                 //Console.Out.WriteLine("\nOrder: Calculated discounted total={0} (expected: {1})\n",
 87                 //                          result, 25);
 88                 //Console.ReadLine();
 89             }
 90             catch (Exception ex)
 91             {
 92                 MessageBox.Show(ex.Message);
 93             }
 94         }
 95 
 96         private void frmDiscountRBE_Load(object sender, EventArgs e)
 97         {
 98 
 99         }
100       
101     }
102 }

　　运行程序，界面如下：

数量>40，折扣0.7	数量大于10且小于40，折扣0.8