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 

 <?xml version="1.0" encoding="UTF-8"?>
 <xBusinessRules xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="xBusinessRules.xsd">
     <!-- 全局变量-->
     <Integer id="10i" value="10"/>
     <Integer id="40i" value="40"/>
     <ObjectLookup id="QuantityOrdered" objectId="CurrentOrder" member="Quantity"/>
     <Logic>
         <If>
             <And>
                 <GreaterThanEqualTo leftId="ClientRating" rightId="ClientRatingThreshold">
                       <!-- CurrentOrder为订单对象-->
                     <ObjectLookup id="ClientRating" objectId="CurrentOrder" member="ClientRating"/>
                     <String id="ClientRatingThreshold" value="C"/>
                 </GreaterThanEqualTo>
             </And>
             <Do>
                 <!-- 对于评分高的客户指定的折扣策略 Discount rules for high rate customers -->
                 <Logic>
                     <If>
                         <And>
                             <GreaterThan leftId="QuantityOrdered" rightId="40i"/>
                         </And>
                         <Do>
                           <!-- AppliedDiscount为应用的折扣-->
                             <Evaluate id="AppliedDiscount">
                               <!-- Percent为折扣比例-->
                                 <Parameter name="Percent" value=".7"/>
                             </Evaluate>
                         </Do>
                     </If>
                     <ElseIf>
                         <And>
                             <GreaterThan leftId="QuantityOrdered" rightId="10i"/>
                         </And>
                         <Do>
                             <Evaluate id="AppliedDiscount">
                                 <Parameter name="Percent" value=".8"/>
                             </Evaluate>
                         </Do>
                     </ElseIf>
                     <Else>
                         <Evaluate id="AppliedDiscount">
                             <Parameter name="Percent" value=".9"/>
                         </Evaluate>
                     </Else>
                 </Logic>
             </Do>
         </If>
         <Else>
             <!-- 对于评分低的客户指定的折扣策略 Discount rules for low rate customers -->
             <Logic>
                 <If>
                     <And>
                         <GreaterThan leftId="QuantityOrdered" rightId="40i"/>
                     </And>
                     <Do>
                         <Evaluate id="AppliedDiscount">
                             <Parameter name="Percent" value=".9"/>
                         </Evaluate>
                     </Do>
                 </If>
                 <Else>
                     <Evaluate id="AppliedDiscount">
                         <Parameter name="Percent" value="1"/>
                     </Evaluate>
                 </Else>
             </Logic>
         </Else>
     </Logic>
 </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：

 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Data;
 using System.Drawing;
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 using System.Windows.Forms;
 using System.Collections;
 using NxBRE.FlowEngine;
 using NxBRE.FlowEngine.IO;
 using BREFactory = NxBRE.FlowEngine.Factories.BREFactory;
 using Reflection = NxBRE.Util.Reflection;
 namespace WinApp
 {
     public partial class frmDiscountRBE : Form
     {
         public frmDiscountRBE()
         {
             InitializeComponent();

         }

         /// <summary>
         /// 规则xml文件名称
         /// </summary>
         public const string FLOW_RULES_FILENAME = "discount.xbre";
         public const string ORDER = "CurrentOrder";
         public const string APPLIED_DISCOUNT = "AppliedDiscount";
         public const string PERCENT = "Percent";
         /**/
         /// <summary>
         /// 定单
         /// </summary>
         struct Order
         {
             public Int32 Quantity;
             public Double TotalCost;
             public string ClientRating;
             public Order(int _q, double _t, string _c)
             {
                 this.Quantity = _q;
                 this.TotalCost = _t;
                 this.ClientRating = _c;
             }
         }
         /**/
         /// <summary>
         /// 计算结果
         /// </summary>
         /// <param name="aBRC">规则引挚上下文</param>
         /// <param name="aMap"></param>
         /// <param name="aStep"></param>
         /// <returns>结果</returns>
         static object AppliedDiscount(IBRERuleContext aBRC, IDictionary aMap, object aStep)
         {
             Order _order = (Order)aBRC.GetObject(ORDER);
             double _d = Convert.ToDouble(Reflection.CastValue(aMap[PERCENT], typeof(double)));
             return _order.TotalCost * _d;
         }
         private void btnDiscount_Click(object sender, EventArgs e)
         {
             try
             {
                 //载入规则
                 IRulesDriver rulesDriver = new XBusinessRulesFileDriver(FLOW_RULES_FILENAME);
                 //工厂
                 BREFactory breFactory = new BREFactory();
                 //引挚实例
                 IFlowEngine bre = breFactory.NewBRE(rulesDriver);
                 //委托实例
                 ExecuteRuleDelegate executeRuleDelegate = new ExecuteRuleDelegate(AppliedDiscount);
                 bre.RuleContext.SetFactory(APPLIED_DISCOUNT, new BRERuleFactory(executeRuleDelegate));
                 //设置规则引挚环境变量
                 //Order order = new Order(5, 25, "A");
                 Order order = new Order(Int32.Parse(this.txtQuantity.Text), Double.Parse(this.txtTotalCost.Text), this.txtClientRating.Text);
                 bre.RuleContext.SetObject(ORDER, order);
                 //执行
                 bre.Process();
                 //得到执行结果
                 double result = (double)bre.RuleContext.GetResult(APPLIED_DISCOUNT).Result;

                 this.txtPayCost.Text = result.ToString();
                 this.txtPayCost.ReadOnly = true;
                 //Console.Out.WriteLine("\nOrder: Calculated discounted total={0} (expected: {1})\n",
                 //                          result, 25);
                 //Console.ReadLine();
             }
             catch (Exception ex)
             {
                 MessageBox.Show(ex.Message);
             }
         }

         private void frmDiscountRBE_Load(object sender, EventArgs e)
         {

         }

     }
 }

　　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