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// Design Patterns · 10

Facade

Many parts to coordinateleads toOne simple entry point

One simple front door to a complicated subsystem.

How it fits together

Facade structure«client»CheckoutEndpointPost(request)CheckoutFacadePlaceOrderAsync(req)InventoryServicePricingServiceTaxServicePaymentServiceone call1 reserve2 price3 tax4 charge
uses / calls· numbered steps replay in order
  • CheckoutEndpoint uses / calls CheckoutFacade (one call)
  • CheckoutFacade uses / calls InventoryService (1 reserve)
  • CheckoutFacade uses / calls PricingService (2 price)
  • CheckoutFacade uses / calls TaxService (3 tax)
  • CheckoutFacade uses / calls PaymentService (4 charge)

Spot it

  • Callers orchestrate five services for one task
  • The same call sequence copied across features
  • You must learn a subsystem just to use it

It costs

It can grow into a god class, and it hides options some callers still need.

In code

public sealed class CheckoutFacade(    IInventoryService inventory,    IPricingService pricing,    ITaxService tax,    IPaymentService payment){    public async Task<Receipt> PlaceOrderAsync(CheckoutRequest request, CancellationToken ct)    {        await inventory.ReserveAsync(request.Lines, ct);        var subtotal = await pricing.PriceAsync(request.Lines, ct);        var total = subtotal + await tax.CalculateAsync(subtotal, request.Address, ct);        var charge = await payment.ChargeAsync(request.PaymentToken, total, ct);        return new Receipt(charge.Id, total);    }}
Go deeperThe full explanation and what to ask for · 1 min readExpand

A facade gives a simple interface to a set of classes that are complicated to use together. It does not forbid direct access; it just makes the common path easy.

A facade that keeps absorbing business rules turns into a god object. One that maps one-to-one onto a single service adds a layer without simplifying anything.

A module's public API in a modular monolith is a facade over its internals. Adapter converts one interface to another; facade simplifies many behind one.

Ask for it

  • facade
  • subsystem
  • simplified interface
  • orchestration
  • module public API

Checkout code calls inventory, pricing, tax and payment services in sequence from three places. Create a CheckoutFacade with one PlaceOrderAsync(request) method that orchestrates them, and make all callers use only that.

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