Performing calculations with Calculators in Umbraco Commerce.

Calculators are small service implementations with the sole responsibility of calculating prices for a given aspect of an Order. There are five main Calculator service interfaces in Umbraco Commerce:

  • IShippingCalculator - Responsible for calculating the Shipping Method price/tax rate of a given Shipping Method.

  • IPaymentCalculator - Responsible for calculating the Payment Method price/tax rate of a given Payment Method.

  • IProductCalculator - Responsible for calculating the Product unit price/tax rate of a given Product.

  • IOrderLineCalculator - Responsible for calculating the price/tax rate of a given OrderLine.

  • IOrderCalculator - Responsible for calculating the entire Order.

All Calculator services can be replaced with alternative implementations should you wish to change how Umbraco Commerce performs its calculations.

Defining a Custom Calculator Implementation

The individual Calculator interfaces may differ but the process for defining a custom Calculator implementation is the same for all of them. It is possible to create a new class that implements the default system Calculator that you wish to replace. You can then override the relevant calculation methods.

public class MyProductCalculator : ProductCalculator
    public MyProductCalculator(ITaxService taxService, IStoreService storeService)
        : base(taxService, storeService)
    { }

    public override TaxRate CalculateProductTaxRate(IProductSnapshot productSnapshot, TaxSource taxSource, TaxRate fallbackTaxRate)
        // Do custom tax rate calculation here

    public override Price CalculateProductPrice(IProductSnapshot productSnapshot, Guid currencyId, TaxRate taxRate)
        // Do custom price calculation here

Registering a custom Calculator implementation

Calculators are registered via the IUmbracoCommerceBuilder interface using the AddUnique<TServiceInterface, TReplacementService>() method on the Services property. The TServiceInterface parameter in this case is the Calculator interface Type you wish to replace and TReplacementService is the Type of your custom Calculator implementation.

public static class UmbracoCommerceUmbracoBuilderExtensions
    public static IUmbracoCommerceBuilder AddMyServices(IUmbracoCommerceBuilder builder)
        // Replacing the product calculator implementation
        builder.Services.AddUnique<IProductCalculator, MyProductCalculator>();

        // Return the builder to continue the chain
        return builder;

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