如何编写此 LINQ 以应用业务逻辑？

Question

我正在尝试应用一些业务逻辑。
我关于在以下对象模型上使用 LINQ 以应用业务逻辑的问题。我相应地填充了以下对象：

public class Waiver
{
   public string Id { get; set; }
   public int Type { get; set; }
   public decimal Amount { get; set; }
}

要应用的业务逻辑：

1.) 应用订单项豁免
如果 LineItem Waiver [Type] 为 1111，则从单价中扣除 LineItem Waiver 金额
如果 LineItem Waiver [Type] 为 2222，则减去 LineItem WaiverAmount 作为单价的百分比
如果 LineItem Waiver [Type] 为 3333，则减去 LineItem Waiver 金额（行价格 = 数量 * 单价）
如果 LineItem Waiver [Type] 为 4444，则将 LineItem Waiver 金额作为离线价格的百分比扣除

2.) 申请订单豁免
如果订单豁免 [类型] 为 4444，则在应用订单项豁免后从总订单价格中扣除订单豁免金额
如果订单豁免 [类型] 为 8888，则在应用 LineItem 豁免后，将订单豁免金额作为订单价格的百分比扣除

实现这一目标的最佳方法是什么？

GetWaivedPrice(decimal unitPrice, int qty, IEnumerable<Waiver> waiver)

GetWaivedPrice 可以写成单个 LINQ 方法，并为所有折扣类型提供适当的映射吗？

这就是我想要实现的目标，最好是编写良好的 LINQ 方法：

private decimal GetWaivedPrice(decimal unitPrice, int qty, 
                                           IEnumerable<Waiver> waiver)
        {
            //Pseudo code shown for clarifying intent
            decimal waivedLineItemAmount = 0m;

            if waiver.Select(d => d.Type == 1111)
            //then apply the business logic on the unit price accordingly        
            if waiver.Select(d => d.Type == 2222)
            //then apply the business logic on the unit price accordingly  
            if waiver.Select(d => d.Type == 3333)
            //then apply the business logic on the unit price accordingly  

            return waivedLineItemAmount;

        }

Answer 1

我在这里看不到 LINQ 的情况。只需依次申请每个Waver。

    private decimal GetWaivedPrice(decimal unitPrice, int qty, 
                                       IEnumerable<Waiver> waiver)
    {
        //Pseudo code shown for clarifying intent
        decimal waivedLineItemAmount = 0m;

        //apply all waivers
        foreach (var w in waiver) {
         switch (w.Type) { 
          case 1111:
           waivedLineItemAmout += someComputation();
           break;
          case 2222:
           waivedLineItemAmout += someComputation();
           break;
          case 3333:
           waivedLineItemAmout += someComputation();
           break;
         }
        }

        return waivedLineItemAmount;
    }

如果您坚持使用 LINQ 和纯函数式风格，您可以使用 Enumerable.Aggregate 来表述这一点，但在这里一个简单的循环似乎就可以了。

Answer 2

我没有看到对 linq 本身的需求，但可能是面向对象的设计。

我会改为让豁免处理方法调用中的业务逻辑，例如您现在拥有的。

public class Waiver
{
   public string Id { get; set; }
   public int Type { get; set; }
   public decimal Amount { get; set; }

   public decimal GetWaivedPrice(decimal unitPrice, int qty) { ... }

}

这样做可以促进任何未来的 linq 预测或操作，例如这种分组，当然还可以集中业务逻辑以供将来维护。

var groupedResult = myWaivers.Select(wv => new
    {
       Type = wv.Type,
       WaivedPrice = wv.GetWaivedPrice( unitPrice, qty)
    } )
                             .GroupBy(wv => wv.Type);

Answer 3

怎么样：

private static Dictionary<int, Func<decimal, int, Waiver, decimal>> _logic
    = new Dictionary<int, Func<decimal, int, Waiver, decimal>>() {
        { 2222, (a, q, w) => a + w.Amount },
        { 3333, (a, q, w) => a + w.Amount },
        { 3333, (a, q, w) => a + w.Amount }
    };

private static decimal GetWaivedPrice(decimal unitPrice, int qty, 
                                   IEnumerable<Waiver> waiver)
{
    return waiver.Aggregate(0m, (a, s) => _logic[s.Type](a, qty, s), a => a);
}

当然，您必须使用折扣逻辑更新 _logic 字典才能使其正常工作。

Answer 4

业务规则被隔离到单独的关注点（推导和策略）中，现在它非常类似于 LINQ！

// Create a data structure to model the deductions themselves
public class LineItemDeduction
{
    public decimal UnitPriceAmount { get; set; }
    public decimal UnitPricePercentage { get; set; }
    public decimal LinePriceAmount { get; set; }
    public decimal LinePricePercentage { get; set; }

    // Assumed that waivers are distinct and are not composed together, only applied on the listed price.
    public decimal CalculateWaivedPrice(decimal unitPrice, int qty)
    {
        return ((unitPrice - UnitPriceAmount - (unitPrice * UnitPricePercentage)) * qty) - LinePriceAmount - (unitPrice * qty * LinePricePercentage);
    }
}

// Calculate the deductions
private LineItemDeduction CalculateLineItemDeductionStrategy(LineItemDeduction deduction, Waiver waiver)
{
    switch (waiver.Type) { 
      case 1111:
       deduction.UnitPriceAmount += waiver.Amount;
       break;
      case 2222:
       deduction.UnitPricePercentage += waiver.Amount;
       break;
      case 3333:
       deduction.LinePriceAmount += waiver.Amount;
       break;
      case 4444:
       deduction.LinePricePercentage += waiver.Amount;
       break;
     }

     return deduction;
}

// Extension method only for LineItem but it's the same principle for order waivers
public static decimal GetWaivedPrice(this IEnumerable<Waiver> waivers, decimal unitPrice, int qty, Func<LineItemDeduction, Waiver, LineItemDeduction> deductionStrategy)
{
    return waivers.Aggregate(
        new LineItemDeduction(),
        deductionStrategy,
        d => d.CalculateWaivedPrice(unitPrice, qty)
    );
}

// Now to get the waived price
var waivedPrice = waivers.GetWaivedPrice(unitPrice, qty, CalculateLineItemDeductionStrategy);