基於NXBRE規則引擎實現的柔性折扣策略

　　規則引擎由推理引擎發展而來，是一種嵌入在應用程式中的組件，實現了將業務決策從應用程式代碼中分離出來，並使用預定義的語義模塊編寫業務決策。接受數據輸入，解釋業務規則，並根據業務規則做出業務決策。應用背景： 企業級管理者對企業IT系統的開發有著如下的要求：

1. 為提高效率，管理流程必須自動化，即使現代商業規則異常複雜。

2. 市場要求業務規則經常變化，IT系統必須依據業務規則的變化快速、低成本的更新。

3. 為了快速、低成本的更新，業務人員應能直接管理IT系統中的規則，不需要程式開發人員參與。

　　下麵介紹一個開源的引擎（NXBRE  Rule-engine）實現動態折扣價格計算：

　　折扣邏輯配置使用XML（擴展名.xbre）為文件，後期修改XML打折策略，在程式代碼無需修改的情況，實現柔性折扣策略的目的。

　　折扣規則文件：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     <!-- 全局變數-->
 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為訂單對象-->
12                     <ObjectLookup id="ClientRating" objectId="CurrentOrder" member="ClientRating"/>
13                     <String id="ClientRatingThreshold" value="C"/>
14                 </GreaterThanEqualTo>
15             </And>
16             <Do>
17                 <!-- 對於評分高的客戶指定的折扣策略 Discount rules for high rate customers -->
18                 <Logic>
19                     <If>
20                         <And>
21                             <GreaterThan leftId="QuantityOrdered" rightId="40i"/>
22                         </And>
23                         <Do>
24                           <!-- AppliedDiscount為應用的折扣-->
25                             <Evaluate id="AppliedDiscount">
26                               <!-- Percent為折扣比例-->
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             <!-- 對於評分低的客戶指定的折扣策略 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>

　　所有的業務邏輯都在discount.xbre 中定義，下麵我們定義一個窗體來解析折扣邏輯並顯示計算的結果：

  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         /// 規則xml文件名稱
 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         /// 定單
 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         /// 計算結果
 51         /// </summary>
 52         /// <param name="aBRC">規則引摯上下文</param>
 53         /// <param name="aMap"></param>
 54         /// <param name="aStep"></param>
 55         /// <returns>結果</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                 //載入規則
 67                 IRulesDriver rulesDriver = new XBusinessRulesFileDriver(FLOW_RULES_FILENAME);
 68                 //工廠
 69                 BREFactory breFactory = new BREFactory();
 70                 //引摯實例
 71                 IFlowEngine bre = breFactory.NewBRE(rulesDriver);
 72                 //委托實例
 73                 ExecuteRuleDelegate executeRuleDelegate = new ExecuteRuleDelegate(AppliedDiscount);
 74                 bre.RuleContext.SetFactory(APPLIED_DISCOUNT, new BRERuleFactory(executeRuleDelegate));
 75                 //設置規則引摯環境變數
 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                 //執行
 80                 bre.Process();
 81                 //得到執行結果
 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 }

　　運行程式，界面如下：

數量>40，折扣0.7	數量大於10且小於40，折扣0.8