Where should I implement the external API calls logic in Clean Architecture?

In Clean Architecture, the logic for external API calls should be implemented in the Infrastructure Layer. This approach ensures that the core business logic remains independent of external dependencies, adhering to the principles of Clean Architecture.

Explanation

1. Separation of Concerns: Clean Architecture emphasizes the separation of concerns by organizing the application into distinct layers. The core layers (Domain and Application) should not depend on external systems directly. Instead, they should rely on abstractions (interfaces) that are implemented in the outer layers.

2. Infrastructure Layer: The Infrastructure Layer is responsible for handling all external interactions, including database access, file systems, and external API calls. By placing the API call logic in this layer, you ensure that the core business logic (contained in the Domain and Application layers) remains unaffected by changes in external systems.

3. Abstractions and Interfaces: In the Domain or Application layer, you define interfaces that represent the required operations. The Infrastructure Layer then provides concrete implementations of these interfaces. This allows the core layers to interact with external systems through well-defined contracts, promoting loose coupling and easier testing.

Practical Implementation

• Define Interfaces: In the Domain or Application layer, define interfaces for the external API interactions. For example, if you need to interact with a payment gateway, you might define an interface like IPaymentGateway.

• Implement Interfaces: In the Infrastructure Layer, provide concrete implementations of these interfaces. This is where you write the actual logic for making API calls using libraries like HttpClient in .NET, Axios in JavaScript, or Dio in Flutter.

• Dependency Injection: Use dependency injection to inject the concrete implementations into the core layers. This allows you to easily swap out implementations, for example, for testing purposes.

Example

Domain Layer

public interface IPaymentGateway
{
    Task<PaymentResponse> ProcessPayment(PaymentRequest request);
}

Infrastructure Layer

public class PaymentGateway : IPaymentGateway
{
    private readonly HttpClient _httpClient;

    ...