What is Facade Pattern?
Exposing the simplistic interface of anything complex is a Facade. For example, when you place an order for Pizza delivery, the application hides the complex process behind Pizza Delivery to your door.
A successful Pizza delivery order requires multiple services to participate. Facade Pattern exposes the participating services such as Store Availability, Delivery Staff Availability, inventory of items, and others via a straightforward interface. With a straightforward interface, it achieves the following objectives:
- It reduces the indirect coupling and eliminates direct coupling between the Consumer of the Facade and participating services.
- It hides and simplifies the interaction between the Consumer and the Facade.
- It allows you to replace the sub-system without impacting the Consumer.
The facade pattern is similar to Adapter Pattern, but it hides sub-systems from its Consumer while the Adapter pattern focuses on the object or one sub-system.
When to use Facade Pattern?
You should refactor towards Facade Pattern when:
- Interaction between the consumer class and sub-systems is getting complex and straightforward, and a stable interface can provide the most functionality of complex sub-systems.
- Replacing Legacy old sub-system(s).
How to implement it?
The Facade Pattern is a container class that depends upon two or more classes (sub-systems) to complete the transaction it exposes via its interface to the consumer class. A skeleton of example class is below:
//A facade which depends upon two services
private readonly DeliveryRiderAvailability _riderAvailability;
private readonly PaymentProcessor _paymentProcessor;
//Dependcies are injected using DI Container
public OrderServiceFacade(DeliveryRiderAvailability riderAvailability, PaymentProcessor paymentProcessor)
_riderAvailability = riderAvailability;
_paymentProcessor = paymentProcessor;
public Task PlaceOrder(Order order)
//Other steps via other sevices.
//Handle errors of participating services more gracefully
throw new NotImplementedException();
Structure of Facade Pattern
The structure of Facade patter in form of class diagram is below:
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