Use APIs in conjunction with promotions and discounts

public class CustomGetCartLineMapper : GetCartLineMapper
{
    public CustomGetCartLineMapper(ICurrencyFormatProvider currencyFormatProvider, IObjectToObjectMapper objectToObjectMapper, IUrlHelper urlHelper, IRouteDataProvider routeDataProvider)
        : base(currencyFormatProvider, objectToObjectMapper, urlHelper, routeDataProvider)
    {
    }

    public override CartLineModel MapResult(GetCartLineResult serviceResult, HttpRequestMessage request)
    {
        var result = base.MapResult(serviceResult, request);

        result.Properties.Add("promotionName", serviceResult.CartLine.PromotionResult?.Promotion.Name);

        return result;
    }
}
       ```
The image below shows the new, updated response with the "promotionName" custom property.

![](https://files.readme.io/70749fc-4_2_using_apis_with_promotions_1_1_1.png)

### Using the Promotions API

![](https://files.readme.io/6d88147-4_2_using_apis_with_promotions_1_2_1.png)

The image below shows the new, updated response with the "promotionName" custom property.

This solution is very similar to the solution used in <<product-name>> 4.3 to indicate promotions at the order line or order level.

```prettyprint
public class CustomGetPromotionMapper : GetPromotionMapper
{
    protected readonly ICartService CartService;

    public CustomGetPromotionMapper(IObjectToObjectMapper objectToObjectMapper, IUrlHelper urlHelper, ICartService cartService)
        : base(objectToObjectMapper, urlHelper)
    {
        this.CartService = cartService;
    }

    public override PromotionModel MapResult(GetPromotionResult serviceResult, HttpRequestMessage request)
    {
        var result = base.MapResult(serviceResult, request);

        var cartId = request.GetRouteData().Values["cartid"].ToString();

        var cart = this.CartService.GetCart(new GetCartParameter
        {
            CartId = cartId.ToCurrentOrGuid(),
            GetCartLineResults = true
        });

        foreach (var cartLine in cart.CartLineResults.Select(o => o.CartLine))
        {
            if (cartLine.PromotionResult?.Promotion.Id == serviceResult.Promotion.Id)
            {
                result.Properties.Add("orderLineId", cartLine.Id.ToString());
            }
        }

        return result;
    }
}
      ```
The following custom mapper adds the matching "orderLineId" to the promotion response. This indicates that the promotion applies to the cart line level. If this custom property does not exist in the response, this indicates that the promotion applies to the cart level.

1. Create a custom mapper class, but this time inherit from the    **GetPromotionMapper** base class.

2. Again, override the **MapResult** method and be sure to call the    base method before doing any work.

3. In this method, you can access the **cartid** from the incoming    request.

   ```prettyprint
   var cartId = request.GetRouteData().Values["cartid"].ToString();          ```
4. Using the **cartid** you can access the current cart.

5. Then, just like before, you can add any additional information you    need to the **Properties** collection of the **PromotionModel**.

![](https://files.readme.io/154d1e3-4_2_using_apis_with_promotions_1_3_1.png)

The image below shows a response with the both a cart and order line level promotion applied. The first promotion object contains an "orderLineId" property that has a null value. This indicates that the promotion was applied at the order level. In the second promotion object, the "orderLineId" property contains the id of the matching order line to which the promotion was applied.

The endpoint `/api/v1/carts/current` returns order line data alongside the promotion data. This can help determine which promotions are applied at the order or order line level.