一个简单的规则引擎例子

本例使用的规则引擎包是RulesEngine，关于RulesEngine的介绍，请自行补充，这里只是一个极简单使用场景。

例子大体就是用户有一些优惠券，系统会根据用户订单情况，筛选可以使用的优惠券供用户选择，用户选择后会计算出优惠后金额。

代码相对简单，就不一一介绍了，奉上service中的代码：

using Microsoft.Extensions.Logging;
using RulesEngine.Extensions;
using RulesEngine.Models;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;namespace RulesEngineSample.Services
{public class CouponService : ICouponService{private readonly ILogger<CouponService> _logger;private readonly List<Coupon> _userCoupons;private readonly Order _order;private readonly User _user;public CouponService(ILogger<CouponService> logger){_logger = logger;//假装用户用的优惠券_userCoupons = new List<Coupon>() {new Coupon{ID = 1,Code="YH01",Name = "满500减20",BeginTime = DateTime.Parse("2021-01-01"),EndTime = DateTime.Parse("2021-06-01"),Expression = "input1.Details.Sum(s => s.Price * Convert.ToDecimal(s.Quantity))>= 500",Symbol="-",Number=20},new Coupon{ID = 2,Code="YH02",Name = "新人5元券",BeginTime = DateTime.Parse("2021-01-01"),EndTime = DateTime.Parse("2021-06-01"),Expression = "input1.Details.Count>0",Symbol="-",Number=5},new Coupon{ID = 3,Code="YH03",Name = "商品C五折",BeginTime = DateTime.Parse("2021-01-01"),EndTime = DateTime.Parse("2021-06-01"),Expression = "input1.Details.Where(s=>s.GoodsID==\"SP0000003\").Count()>0",Symbol="*",Number=0.5f,GoodsID="SP0000003"},};//假装当前用户的订单_order = new Order{OrderNo = "NO00000001",OrderTime = DateTime.Now,Details = new List<Detail>{new Detail{ GoodsID="SP0000001", Name="商品A", Price=12.5m, Quantity=3},new Detail{ GoodsID="SP0000002", Name="商品B", Price=100m, Quantity=4},new Detail{ GoodsID="SP0000003", Name="商品C", Price=22.3m, Quantity=5},}};_user = new User { ID = 1, UserName = "zhangsan" };}/// <summary>/// 适配优惠券/// </summary>/// <returns></returns>public async Task<string> SelectCouponAsync(){var workRules = new RulesEngine.Models.WorkflowRules();workRules.WorkflowName = "优惠券";var rules = new List<Rule>();foreach (var coupon in _userCoupons.Where(s => s.BeginTime < DateTime.Now && s.EndTime > DateTime.Now)){var rule = new Rule{RuleName = coupon.Name,SuccessEvent = coupon.Code,ErrorMessage = "规则应用失败",ErrorType = ErrorType.Error,RuleExpressionType = RuleExpressionType.LambdaExpression,Expression = coupon.Expression};rules.Add(rule);}workRules.Rules = rules;var rulesEngine = new RulesEngine.RulesEngine(new WorkflowRules[] { workRules }, _logger, new ReSettings());var ruleResults = await rulesEngine.ExecuteAllRulesAsync("优惠券", _order, _user);// var valueCoupons = new List<string>();//处理结果var discountCoupons = new StringBuilder();foreach (var ruleResult in ruleResults){if (ruleResult.IsSuccess){discountCoupons.AppendLine($"可以使用的优惠券 “{_userCoupons.SingleOrDefault(s => s.Code == ruleResult.Rule.SuccessEvent)?.Name}”, Code是：{ruleResult.Rule.SuccessEvent}");//valueCoupons.Add(ruleResult.Rule.SuccessEvent);}}//resultList.OnSuccess((eventName) =>//{//    discountOffered += $"可以使用的优惠券“{userCoupons.SingleOrDefault(s => s.Code == eventName)?.Name}”,Code是：{eventName} ";//});ruleResults.OnFail(() =>{discountCoupons.AppendLine("您没有适合的优惠券！");});return discountCoupons.ToString();}/// <summary>/// 计算订单支付总额/// </summary>/// <param name="code"></param>/// <returns></returns>public string GetOrderAmount(string code){            var selectCoupon = _userCoupons.SingleOrDefault(s => s.Code == code);var orderAmount = 0m;switch (selectCoupon.Symbol){case "-":orderAmount = _order.Details.Sum(s => s.Price * Convert.ToDecimal(s.Quantity)) - Convert.ToDecimal(selectCoupon.Number);break;case "*":if (!string.IsNullOrWhiteSpace(selectCoupon.GoodsID)){orderAmount = _order.Details.Sum(s => s.Price * Convert.ToDecimal(s.Quantity));var detail = _order.Details.SingleOrDefault(s => s.GoodsID == selectCoupon.GoodsID);if (detail != null){orderAmount -= detail.Price * Convert.ToDecimal(detail.Quantity) * Convert.ToDecimal(1 - selectCoupon.Number);}}else{orderAmount = _order.Details.Sum(s => s.Price * Convert.ToDecimal(s.Quantity)) * Convert.ToDecimal(selectCoupon.Number);}break;}return $"订单总金额：{_order.Details.Sum(s => s.Price * Convert.ToDecimal(s.Quantity)) }，优惠后请支付：{orderAmount}";}}public class Coupon{public int ID { get; set; }public string Code { get; set; }public string Name { get; set; }public DateTime BeginTime { get; set; }public DateTime EndTime { get; set; }public string Expression { get; set; }public string Symbol { get; set; }public float Number { get; set; }public string GoodsID { get; set; }}public class User{public int ID { get; set; }public string UserName { get; set; }}public class Order{public string OrderNo { get; set; }public DateTime OrderTime { get; set; }public List<Detail> Details { get; set; }}public class Detail{public string GoodsID { get; set; }public float Quantity { get; set; }public decimal Price { get; set; }public string Name { get; set; }}
}

api /selectcoupon是查询可使用的优惠券