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 |
时间： 2024-10-13 10:38:31