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