Is it possible to implement custom validation on a IRuleValue in a custom benefit?

Question

I have a custom benefit that contains a single property for the BizFX user to enter:

public class GetFreeItemAction : ICartLineAction
{
    public IRuleValue<string> SellableItemId { get; set; }
}

Is it possible to validate the value of SellableItemId? I would like the user to enter the ID on the format Entity-SellableItem-1234.

If this is not possible, I wonder if it is possible to reuse the "special" Item Id field that is used in some qualifications, on a custom benefit? An example: The Is Item Pre-orderable qualification contains an Item Id field that validates if the item actually exists in the selected catalog:

I am on Sitecore XC 9.1.

Answer 1

We do something similar in our OSS promotion extensions: Nyxie.

It should be enough to just rename the SellableItemId property to TargetItemId. The default promotion plugin contains a GetPromotionBenefitDetailsViewBlock that will automatically add the Catalog and Item Ids input fields to the Benefit, when it encounters a field named TargetItemId.