How to create a custom benefit

Question

I have created a custom benefit/action for a promotion. When user applies the promo, nothing happens. There are no errors when i check in debug. The code is hit though.

public void Execute(IRuleExecutionContext context)
{
    .....code
    ......
   ApplyDiscountPercentForLineItems(commerceContext,  validCartLineItems, discountPercent, 
  awardingBlockName);
}

public static void ApplyDiscountPercentForLineItems(CommerceContext commerceContext, 
                     List<CartLineItem> validCartLineItems, decimal discountPercent, 
                     string awardingBlockName)
{
   var cart = (commerceContext.Objects.OfType<Cart>()).FirstOrDefault();
   var totals = (commerceContext.Objects.OfType<CartTotals>()).FirstOrDefault();

   var model = commerceContext.Objects.OfType<PropertiesModel>().FirstOrDefault();

   foreach (var line in validCartLineItems)
   {
     var discount = commerceContext.GetPolicy<KnownCartAdjustmentTypesPolicy>().Discount;
     var d = discountPercent;

     if (commerceContext.GetPolicy<GlobalPricingPolicy>().ShouldRoundPriceCalc)
     {
       d = decimal.Round(d, commerceContext.GetPolicy<GlobalPricingPolicy>().RoundDigits,
           commerceContext.GetPolicy<GlobalPricingPolicy>().MidPointRoundUp ? 
           MidpointRounding.AwayFromZero : MidpointRounding.ToEven);
     }

    decimal amount;    
    var currentAmount = totals.Lines[line.Id].SubTotal.Amount;    
    amount = currentAmount - (currentAmount * d / 100);
    amount = amount * decimal.MinusOne;
    totals.Lines[line.Id].SubTotal.Amount += amount;

    var item = new CartLineLevelAwardedAdjustment
    {
      Name = (string)model.GetPropertyValue("PromotionText"),
      DisplayName = (string)model.GetPropertyValue("PromotionCartText"),
      Adjustment = new Money(commerceContext.CurrentCurrency(), amount),
      AdjustmentType = discount,
      IsTaxable = false,
      AwardingBlock = awardingBlockName,
      IncludeInGrandTotal = true
    };

   line.Adjustments.Add(item);

   line.GetComponent<MessagesComponent>().AddMessage(
   commerceContext.GetPolicy<KnownMessageCodePolicy>().Promotions, 
   $"PromotionApplied: {model.GetPropertyValue("PromotionId")}");
 }           
}

Answer 1

I had this issue previously and it was because by my custom benefit was implementing IAction and not ICartLineAction.

As part of the benefit resolution process the IDiscoverPromotionsPipeline is executed and it contains the FilterPromotionsByBenefitTypeBlock, which excludes any benefits that dont implement ICartLineAction.